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Circulation. 1997;96:3094-3103

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(Circulation. 1997;96:3094-3103.)
© 1997 American Heart Association, Inc.

Articles

Importance of Endogenous Adenosine During Ischemia and Reperfusion in Neonatal Porcine Hearts

Hilchen T. Sommerschild, MD; Frank Grund, MD; Jon Offstad, MD, PhD; Per Jynge, MD, PhD; Arnfinn Ilebekk, MD, PhD; ; Knut A. Kirkebøen, MD, PhD

From the University of Oslo, Institute for Experimental Medical Research (H.T.S., F.G., J.O., A.I., K.A.K.) and Department of Anesthesia (K.A.K.), Ullevål Hospital, Oslo, and Institute for Physiology and Biomedical Techniques, Medical Technical Center, Trondheim (P.J.), Norway.


*    Abstract
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 *Abstract
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Background Adenosine has several potentially cardioprotective effects. We hypothesized that the effects of endogenous adenosine vary with degree of ischemia and that elevating endogenous levels is protective.

Methods and Results Isolated blood-perfused piglet hearts underwent 120 minutes of low-flow ischemia (10% flow) or 90 minutes of zero-flow ischemia, all with 60 minutes of reperfusion. Hearts were treated with either saline, the adenosine receptor blocker 8-sulfophenyltheophylline (8SPT, 300 µmol · L-1), or the nucleoside transport inhibitor draflazine (1 µmol · L-1). In separate groups, biopsies were obtained before and at the end of ischemia. Compared with saline, 8SPT did not significantly alter functional recovery in either protocol. Draflazine significantly improved percent recovery of left ventricular systolic pressure both in the low-flow protocol (92±3% versus 75±2% [saline] and 73±3% [8SPT], P<.001 for both) and in the zero-flow protocol (76±3% versus 59±4% [saline] and 46±9% [8SPT], P<.05 for both). In the zero-flow protocol, draflazine also significantly reduced ischemic contracture and release of creatine kinase. Tissue adenosine at the end of ischemia was elevated by draflazine compared with saline-treated hearts: after low-flow ischemia to 0.10±0.05 versus 0.00±0.00 µmol · g-1 dry wt (P<.05) and after zero-flow ischemia to 1.73±0.82 versus 0.15±0.03 µmol · g-1 dry wt (P<.05).

Conclusions In neonatal porcine hearts, endogenous adenosine produced during ischemia does not influence ischemic injury or functional recovery. Elevating endogenous adenosine by draflazine elicits cardioprotection in both low-flow and zero-flow conditions.


Key Words: adenosine • infarction • ischemia • myocardium • reperfusion


*    Introduction
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 *Introduction
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Adenosine has been shown to attenuate several deleterious effects of ischemia and reperfusion,1 and exogenous administration reduces infarct size,2 attenuates development of stunning,3 4 and mimics ischemic preconditioning.5 Thus, protective effects of exogenous adenosine are achieved, even though the endothelium serves as a barrier for its distribution.6 7

During ischemia, adenosine is endogenously produced because of breakdown of ATP.1 8 Endogenous adenosine has easy access to the interstitial space. However, a cardioprotective role is not intuitive, because adenosine is rapidly taken up by endothelial cells and catabolized or washed out.9 Conflicting data have been reported on the importance of endogenous adenosine produced during LF ischemia.10 11 12 13 14 15 During ZF ischemia, adenosine receptor inhibitors and adenosine deaminase impair functional recovery,16 17 whereas effects on infarct size are conflicting.18 19 20 21 22 Only one of these studies has been performed on neonatal hearts,13 which are more resistant to ischemia than adult hearts23 and differ in adenosine metabolism.24 25 26 The first aim of the present study was therefore to examine the role of endogenous adenosine produced during LF and ZF ischemia. This was achieved by selective blockade of adenosine A1 and A2 receptors with 8SPT.27

An alternative to exogenous administration of adenosine is to elevate levels of endogenous adenosine by inhibiting its degradation. After ZF ischemia, such interventions have been shown to reduce infarct size28 29 30 31 and improve functional recovery.32 33 34 However, negative findings have also been reported.35 36 37 None of these studies were performed in neonatal hearts. To the best of our knowledge, this approach has not previously been investigated in LF ischemia. There are profound differences between LF and ZF ischemia with regard to accumulation of metabolites and ions and formation of free oxygen radicals during reperfusion.38 Formation of adenosine is also related to the degree of ischemia.8 The second aim of the present study was therefore to examine whether elevated endogenous levels of adenosine can induce beneficial effects in LF and ZF conditions. We used draflazine, an inhibitor of the nucleoside transporter, which inhibits uptake of adenosine into endothelial cells and red blood cells and hence prevents intracellular degradation and transport across the endothelium.9 It is selective for the nucleoside transporter and devoid of other known effects.39


*    Methods
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 *Methods
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Animals were maintained and housed in accordance with the conditions set by the Norwegian Council for Animal Research. The investigation conformed with the Guide for the Care and Use of Laboratory Animals, published by the US National Institutes of Health (NIH publication No 85-23, revised 1985).

Heart Excision, Perfusion System, and Perfusate
Piglets were anesthetized with pentobarbital sodium (25 mg · kg-1 IP and {approx}25 mg · kg-1 IV) and given sodium heparin (1000 IU IV) for anticoagulation. Mechanical ventilation through a tracheostoma was performed with a mixture of 50% air/50% oxygen. Hearts were rapidly excised and within seconds placed in 4°C KH buffer. A latex balloon was passed into the left ventricle through the left atrium. Hearts were mounted on the perfusion system by aortic cannulation within 10 minutes after excision, and the pulmonary artery was cannulated. Hearts were retrogradely perfused in a recirculating manner either at constant pressure (70 mm Hg) or at controlled coronary flow with a precisely calibrated pump (Cole Palmer Instruments). The chamber enclosing the heart and other components of the perfusion system were water-jacketed to maintain temperature at 37°C. Details of the system have been described previously.13 40 Oxygenation was achieved by passing a mixture of 95% O2/5% CO2 through the perfusate. The perfusate was filtered by a transfusion filter (20 µm). Hearts were perfused with erythrocyte-enriched KH buffer. Packed human erythrocytes were washed twice with KH buffer (without BSA and insulin). The modified KH solution contained glucose 11 mmol · L-1, BSA (Sigma) 2%, free fatty acids (from the BSA) 0.15 mmol · L-1, insulin (Human Velosulin) 50 IU · L-1, and ions from the following salts (in mmol · L-1): NaCl 118.5, NaHCO3 25.0, KCl 4.7, KH2PO4 1.2, MgSO4 1.2, and CaCl2 2.4. Erythrocytes were then suspended in this solution to provide a hematocrit of {approx}0.20.41

Cardiac Performance Measurements
LV pressure was recorded by the fluid-filled balloon in the left ventricle, connected to a Gould pressure transducer (model P23 Gb, Gould Instruments). HR was derived from the pressure curves. PP was measured through another Gould pressure transducer connected to a side branch of the aortic cannula. Hemodynamic variables were continuously recorded on an eight-channel thermal array oscillographic recorder (model OR 2300, Yokogawa). When high resolution of data was required, the output from this recorder was sampled at 100 Hz. Signals were transformed by an analog-to-digital converter for further computation. LV pressure-volume curves were obtained by adding known fluid volumes into the balloon to increase LVEDP from 0 to 15 mm Hg. The slope of the relation between changes in LV volume and LV diastolic pressure was used to estimate LV diastolic wall stiffness. During ischemia, a rise in LVEDP of 4 mm Hg was defined as ischemic contracture. If LVEDP exceeded 4 mm Hg, fluid was removed from the balloon, after which LVEDP was maintained at 1 mm Hg.

Experimental Procedure and Protocols
Hearts were initially perfused at constant pressure (70 mm Hg), and the first venous effluent was discarded. After 20 to 30 minutes of stabilization, we switched to a flow-controlled mode (2 mL · min-1 · g-1 heart wt).13 40 Hearts were paced via atrial electrodes ({approx}165 bpm). Criteria for entering the study were peak LVSP10 before ischemia >95 mm Hg and pressure-controlled flow <3 mL · min-1 · g-1 heart wt. Coronary flow was reduced stepwise to 50%, 25%, and 10% of control value at 1-minute intervals. After LF ischemia, flow was restored in the same steps. After ZF ischemia, flow was gradually restored within 10 minutes to minimize reperfusion injury. In LF experiments, pacing was stopped 1 minute after 10% flow was established, and during reperfusion, pacing started 1 minute after 100% flow was reached. In ZF experiments, pacing was stopped just as zero flow was reached, and pacing started between 5 and 10 minutes of reperfusion, depending on arrhythmias. If detrimental arrhythmias developed, hearts were defibrillated with electrical pads for internal use (8 J). If conversion was rapidly achieved, the experiment was continued.

Protocols, number of hearts, and time points of acquisition of data and blood samples are shown in Fig 1Down. Hearts were subjected to two different protocols, LF or ZF ischemia, and exposed to saline, 8SPT, or draflazine from 20 minutes before ischemia. Fifty-one piglets were randomized to six groups subjected to LF or ZF ischemia with subsequent reperfusion to obtain functional data and biopsies at the end of reperfusion (part A). Forty-eight piglets were randomized to nine groups in which biopsies were obtained before ischemia (C2) or at end of LF or ZF ischemia to obtain biopsies at these times (part B). At points of data acquisition, perfusate samples were obtained just before recording of LV function, PP, and HR.



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  		Figure 1. Schematic of experimental protocols. Dotted bars indicate ischemia; open bars, 100% flow (2 mL · min-1 · g-1 heart wt). LF protocols: 120 minutes of 10% flow. ZF protocols: 90 minutes of zero flow. Reperfusion period lasted 60 minutes. Saline, 8SPT, or draflazine was added 20 minutes before ischemia. Control measurements before ischemia were made just before administration of pharmacological agents (C1) and just before ischemia (C2). Reduction and restoration of blood flow were done in a stepwise manner. Hearts were not paced during ischemia. {blacktriangleup}, myocardial biopsies; {uparrow}, blood samples and hemodynamic recordings; {uparrow}, hemodynamic recordings.

Metabolic Measurements
Perfusate samples were obtained anaerobically and simultaneously from the pulmonary artery (venous samples) and from a side branch of the aortic cannula (arterial samples). Lactate concentrations were analyzed enzymatically by spectrophotometry.42 Hemoglobin (Hb) was determined in duplicate by the cyanomethemoglobin method. Arterial and venous oxygen saturations (SaO2 and SvO2) were analyzed on an IL 282 CO-Oximeter (Instrumentation Laboratories). Arterial and venous partial pressures of oxygen (PaO2 and PvO2) and partial pressures of carbon dioxide (PaCO2 and PvCO2) and pH were analyzed on an automatic blood gas analyzer (model 945, AVL Biochemical Instruments). Myocardial oxygen consumption (MO2) was estimated by the formula MO2 (µmol · min-1 · 100 g-1)=[(SaO2-SvO2)x62.1xHb/100+(PaO2-PvO2)x0.00141]xCBFx100/MW, where SO2 is oxygen saturation in %, PO2 is partial pressure of oxygen in mm Hg, the constant 62.1 is oxygen binding capacity of Hb in µmol · g-1, Hb is concentration of hemoglobin in g · mL-1, the constant 0.00141 is the solubility constant of oxygen in blood per atmosphere at 37°C in µmol · mL-1 · mm Hg-1, CBF is coronary blood flow in mL · min-1, and MW is myocardial wet weight in g.

Tissue biopsies were obtained by freeze-clamping a part of the LV free wall and thereafter, they were freeze-dried within 24 hours and stored at -70°C before analysis. Biopsies obtained at the end of reperfusion were analyzed enzymatically by luminometry43 and at the end of ischemia by high-performance liquid chromatography.44 Enzyme activity of CK, in IU · L-1, was analyzed enzymatically by fluorescence in arterial and venous perfusate before ischemia and every 15 minutes during reperfusion. Release of CK was calculated by summation of the AV differences and presented as cumulative release. Water content, indicative of cellular edema, was expressed as percent of wet weight. Samples from the left ventricle were blotted to remove excess fluid and dried to constant weight at 37°C.

Pharmacological Agents
All agents were prepared the day of the experiment and circulated for 20 minutes before ischemia. 8SPT (Research Biochemicals Inc, catalog number A013) was dissolved in saline and added to obtain a perfusate concentration of 300 µmol · L-1. It is a water-soluble xanthine derivative that selectively blocks adenosine A1 and A2 receptors,27 relatively equipotent for the two subclasses.

Draflazine was kindly provided by H. Van Belle, Janssen Pharmaceutical, Beerse, Belgium. The agent was dissolved in saline and added to obtain a perfusate concentration of 1 µmol · L-1. It was carefully shielded from exposure to light during storage, preparation, and administration, and the perfusion system was wrapped in cellophane. Draflazine is the active (-)-enantiomer of the nucleoside transporter inhibitor R75231 and is highly potent and selective toward the transporter molecule.9 39 45

Statistical Analysis
Data are presented as mean±SEM. Regression lines between LVSP and LVEDP were calculated, and values for LV function are presented for LVEDP=10 mm Hg (LVSP10). A paired t test was used to assess differences within groups between C1 and C2. The Fisher exact test was used for comparison of proportions. One-way ANOVA, followed by the Student-Newman-Keuls test, was used for analysis of repeated measurements within groups and for comparison of variables between three groups at single time points. MANOVA, followed by the Student-Newman-Keuls test, was used for multiple group comparisons of repeated measurements. A value of P<.05 was considered statistically significant. Power analyses (LVSP10 and CK) are described in the "Results."


*    Results
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 up arrowMethods
 *Results
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A total of 99 piglets were included in the study. In part A, 51 hearts were subjected to either LF or ZF ischemia, followed by 60 minutes of reperfusion. In part B, biopsies were obtained before (C2) or at the end of ischemia from 48 hearts. Pig weight, heart weight, age, and dose of pentobarbital sodium did not differ between groups (Table 1Down). In part A, 14 piglets were excluded (3 in the LF and 11 in the ZF protocol) because of technical problems (4), hemolysis of red blood cells (2), air emboli (3), and unsuccessful defibrillation at reperfusion (5). In part B, 3 piglets were excluded (1 in the LF protocol and 2 in the C2 protocol) because of technical problems (2) and ventricular fibrillation (1). Data are presented from the remaining 82 piglets.


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  		Table 1. Group Characteristics of Parts A and B of the Study

Hemodynamic Effects of 8SPT and Draflazine
In control hearts, there was a significant fall in sHR and PP from C1 to C2. In 8SPT-treated hearts, no changes were observed. In draflazine-treated hearts, the decline in sHR and PP was accentuated. In addition, LVSP and MO2 showed a slight decline. Right before ischemia (C2), PP in draflazine-treated hearts was reduced compared with the other groups.

Mechanical Function and Metabolism During LF Ischemia
Flow reduction to 10% reduced LVSP10, sHR, and MO2 in all groups. There was no significant difference in LVSP10 between groups during ischemia (Fig 2Down). During the first 90 minutes of ischemia, sHR and MO2 were similar in hearts treated with 8SPT or saline (Fig 2Down, Table 2Down), but at end of ischemia both variables were significantly higher in 8SPT-treated hearts (for both; P<.05). During the whole ischemic period, sHR and MO2 were lower in draflazine-treated hearts than in both other groups. Only minor changes in diastolic wall stiffness were found, and none of the hearts developed ischemic contracture.



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  		Figure 2. LVSP10 in % of preischemic values and HR in hearts subjected to 120 minutes of LF (10%) ischemia and 60 minutes of reperfusion. Pacing was discontinued during ischemia. Hearts were treated with either saline ({circ}), 8SPT ({blacksquare}), or draflazine ({blacktriangleup}) before ischemia. Values are mean±SEM. *P<.05, {dagger}P<.01, and {ddagger}P<.001 for draflazine vs both saline and 8SPT.


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  		Table 2. AV Differences for Perfusate pH, PCO2, Lactate, and MO2 in Hearts Subjected to 120 Minutes of LF Ischemia and 60 Minutes of Reperfusion

Arterial pH, PO2, and SO2 were stable during the experimental period. Arterial PCO2 and lactate increased gradually over time, with no differences between groups. During ischemia, all hearts showed signs of anaerobic metabolism (Table 2Up). During the first 90 minutes, AV differences for pH, PCO2, and lactate were similar in hearts treated with saline or 8SPT, but at the end of ischemia, AV differences for pH and PCO2 were significantly higher in 8SPT-treated hearts. In draflazine-treated hearts, there were smaller changes in AV differences for pH and PCO2 during the first 90 minutes of ischemia than in hearts treated with saline or 8SPT. A similar pattern was observed for lactate, but it did not reach statistical significance. At the end of ischemia, AV differences in pH and PCO2 were similar in hearts treated with saline or draflazine.

Mechanical Function During ZF Ischemia
After a complete stop of perfusion, hearts continued to beat vaguely for some minutes. Ischemic contracture developed in hearts treated with saline (8 of 10) and 8SPT (8 of 9), but not in draflazine-treated hearts (0 of 8) (for draflazine versus both other groups, P<.01). Diastolic stiffness increased in all groups during ischemia, but this increase was lower in draflazine-treated hearts (Fig 3Down).



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  		Figure 3. Calculated slope of relation between corresponding values of LV volume and LVEDP in hearts subjected to 90 minutes of ZF ischemia and 60 minutes of reperfusion. Hearts were treated with either saline ({circ}), 8SPT ({blacksquare}), or draflazine ({blacktriangleup}) before ischemia. Values are mean±SEM.

Mechanical Function and Metabolism During Reperfusion After LF Ischemia
During reperfusion, there was immediate recovery in mechanical function (Fig 2Up). Recovery of contractile function was not significantly different in hearts treated with saline compared with hearts treated with 8SPT at any time during reperfusion (see later power analysis). Hearts treated with draflazine showed significantly better recovery of function than the two other groups, with LVSP10 after 60 minutes of reperfusion 92±3% of preischemic value compared with 75±2% in saline-treated hearts (P<.001) and 73±3% in 8SPT-treated hearts (P<.001). During reperfusion, indices of anaerobic metabolism ceased and AV differences in pH, PCO2, and lactate returned to preischemic values in all groups (Table 2Up). Consistent with good functional recovery, MO2 returned to almost preischemic levels. Only in 8SPT-treated hearts was MO2 slightly reduced compared with preischemic values (P<.01).

Mechanical Function and Metabolism During Reperfusion After ZF Ischemia
There was gradual improvement in systolic function during the first 30 minutes of reperfusion, with subsequent stabilization (Fig 4Down). Hearts treated with 8SPT showed a tendency toward reduced recovery compared with saline-treated hearts, but this did not reach statistical significance at any time (see power analysis). Draflazine-treated hearts showed better functional recovery than the two other groups, with LVSP10 after 60 minutes of reperfusion 76±3% of preischemic value compared with 59±4% in saline-treated hearts (P<.05) and 46±9% in 8SPT-treated hearts (P<.05). Diastolic stiffness declined during reperfusion in saline-treated hearts but remained slightly elevated compared with preischemia (Fig 3Up). In 8SPT-treated hearts, stiffness transiently increased during reperfusion and remained elevated compared with preischemia. The slight increase in stiffness in draflazine-treated hearts was fully reversed during reperfusion.



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  		Figure 4. LVSP10, in % of preischemic values, in hearts subjected to 90 minutes of ZF ischemia and 60 minutes of reperfusion. Pacing was discontinued during ischemia. Hearts were treated with either saline ({circ}), 8SPT ({blacksquare}), or draflazine ({blacktriangleup}) before ischemia. Values are mean±SEM. *P<.05 and {dagger}P<.01 for draflazine vs both saline and 8SPT.

Arterial pH, PO2, and SO2 were stable during the experimental period. Arterial PCO2 and lactate increased gradually over time, with no differences between groups. Consistent with incomplete functional recovery, MO2 was significantly reduced in all groups, with no group differences. At 30 minutes of reperfusion, hearts treated with draflazine showed significantly smaller AV differences in pH and PCO2 compared with hearts treated with saline or 8SPT (Table 3Down). The same tendency was observed for lactate, but it did not reach statistical significance. At 60 minutes of reperfusion, all AV differences had returned to preischemic levels.


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  		Table 3. AV Differences for Perfusate pH, PCO2, and Lactate and MO2 in Hearts Subjected to 90 Minutes of ZF Ischemia and 60 Minutes of Reperfusion

Release of CK During Reperfusion
After LF ischemia, release of CK (IU · 100 g-1) was low: 11±2 (saline), 8±2 (8SPT), and 8±3 (draflazine). There were no differences between groups. After ZF ischemia, release of CK was higher: 140±3 (saline), 213±77 (8SPT), and 20±6 (draflazine). Draflazine-treated hearts showed significantly lower release (versus both other groups, P<.05), whereas there was no observed difference between hearts treated with saline or 8SPT (see later power analysis).

Tissue Metabolites and Water Content
Values obtained before (C2) and at the end of ischemia are given in Table 4Down. Before ischemia, there were no differences between groups in either ATP, PCr, or adenosine. In the LF protocol, there were no changes in ATP or PCr either during ischemia or during reperfusion and no differences between groups. At the end of ZF ischemia, ATP and PCr were significantly lower than before ischemia in all groups and significantly lower in hearts treated with 8SPT compared with the two other groups. At the end of reperfusion after ZF ischemia, levels of ATP and PCr were significantly higher in draflazine-treated hearts than in both other groups (for both, P<.05). At the end of both LF ischemia and ZF ischemia, levels of adenosine were significantly increased in hearts treated with draflazine compared with hearts treated with saline or 8SPT. In addition, adenosine/inosine ratios were substantially elevated in draflazine-treated hearts in both protocols (Table 4Down). At the end of reperfusion, adenosine levels were still higher in draflazine-treated hearts in the ZF protocol, but not in the LF protocol. There were no differences in H2O% between groups in either of the protocols (Table 4Down).


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  		Table 4. Tissue Content of ATP, PCr, Adenosine (µmol · g dry wt-1), Adenosine/Inosine Ratio, and Water Content (H2O%) in Hearts Before Ischemia (C2) or at end of ZF or LF Ischemia Without Reperfusion

Analysis of Power
A statistical analysis was performed to measure the probability that true differences in functional recovery and CK release in hearts treated with 8SPT compared with hearts treated with saline were missed because of insufficient sample size (type II error). All power calculations were made at {alpha}=.05.

We calculated the mean of percent recovery of LVSP10 during the stable phase of reperfusion in all groups. The differences between groups in mean recovery in the LF protocol were 16% for saline- versus draflazine-treated hearts (P<.01), 17% for 8SPT- versus draflazine-treated hearts (P<.01), and 2% for 8SPT- versus saline-treated hearts (P=.73). Corresponding values in the ZF protocol were 21% (P<.05), 32% (P<.01), and 12% (P=.19). In the LF protocol, the probability of detecting a 30% alteration in 8SPT-treated hearts compared with saline-treated hearts was 99%. In the ZF protocol, the probability of detecting a 30% alteration in 8SPT-treated hearts compared with saline-treated hearts was 47%. To achieve an 80% probability of detecting this difference, we would have needed 20 animals in each group.

Power calculations were also done for CK release in the ZF protocol. The differences between groups in mean cumulative CK release (IU · 100 g-1) were 120 for saline- versus draflazine-treated hearts, 193 for 8SPT- versus draflazine-treated hearts (for both, P<.05), and 73 for 8SPT- versus saline-treated hearts (P=.29). Draflazine treatment caused an 86% decrease in CK release compared with saline-treated hearts. To achieve an 80% probability of detecting a 50% alteration in 8SPT-treated hearts compared with saline-treated hearts, we would have needed 74 animals in each group.


*    Discussion
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 up arrowMethods
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 *Discussion
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The role of endogenous adenosine was investigated during LF and ZF ischemia and reperfusion in neonatal porcine hearts. Blockade of adenosine receptors did not significantly affect functional recovery in either condition. Elevating adenosine levels by the nucleoside transporter inhibitor draflazine improved functional recovery after both LF and ZF ischemia. Also, in ZF conditions, ischemic contracture and CK release were attenuated.

Methodological Considerations
The isolated heart preparation is a well-established model for studying metabolism and function during both LF and ZF ischemia. Confounding systemic reactions triggered in the intact organism are eliminated, including neurohumoral mechanisms and alterations in plasma levels of bioamines, hormones, and substrates. This allows investigation of intrinsic functional and metabolic properties of the heart in response to ischemia. The erythrocyte-enriched perfusate provides adequate oxygenation at physiological flow rates and enables us to closely mimic LF ischemia, in which rate of washout of metabolites and ions is of crucial importance. This is in sharp contrast to crystalloid-perfused preparations, in which coronary flow has to be 5 to 10 times above normal to ensure adequate oxygenation. In our preparation, we have previously confirmed stable mechanical and metabolic function for at least 3 hours.13 46

In global ischemia, at least two determinants of energy consumption are substantially reduced. First, passive repetitive stretching of the ischemic myocardium is an important determinant for metabolism,46 and second, HR is severely reduced. Also, neonatal hearts tolerate ischemia better than adult hearts.23 Developmental differences in calcium regulation, glycogen content, and enzyme activities in metabolic pathways may contribute to our findings.23 Eventually, the isolation procedure could alter baseline contractile function and responses to ischemia, but all groups would be equally affected.

Role of Endogenous Adenosine Produced During Ischemia
The importance of endogenous adenosine produced during ischemia was investigated by blocking adenosine receptors with 8SPT. This did not affect functional recovery after either LF or ZF ischemia or CK release after ZF ischemia, indicating that the amount of adenosine produced during ischemia is too low to have physiological effects on functional recovery. Our data on LF ischemia are conclusive (see power analysis) and in accordance with previous studies in both isolated13 14 15 and intact hearts.10 In ZF conditions, we cannot rule out that there was a small effect of 8SPT. A tendency toward impaired recovery and increased release of CK was observed, but it did not reach statistical significance. However, we would have needed prohibitively large sample sizes to detect these differences (see power analysis). In ZF ischemia, some studies have shown no effect of 8SPT on infarct size,18 19 20 whereas others have found increased infarction.21 22

During early LF ischemia, there were no differences in mechanical function and metabolism between hearts treated with saline or 8SPT. This is in accordance with previous studies in intact animals10 and neonatal13 and adult15 isolated hearts, in which endogenous adenosine does not affect initial downregulation of function. However, toward the end of ischemia, hearts treated with 8SPT showed increased sHR, MO2, and AV differences for pH and PCO2 and similar tendencies for lactate and LVSP10. These alterations are most likely due to blockade of A1 receptors, which results in increased HR and inotropy. Whereas two studies have shown that antagonism of adenosine with 8SPT13 or adenosine deaminase10 during LF ischemia does not affect metabolism, another study has reported increased release of lactate.14 Discrepancies might be due to degree and duration of flow reduction and the species and age of animals used.

The prominent increase in diastolic stiffness in 8SPT-treated hearts during ZF ischemia is in accordance with earlier works.47 48 49 In 8SPT-treated hearts, we found that diastolic stiffness was transiently further increased during early reperfusion, whereas in saline-treated hearts, stiffness was partially reversed. Also, we found no relation between ATP and PCr levels at the end of ischemia and contracture development during ischemia. Hence, it is likely that contracture development is not only due to a decline in ATP but also may involve other factors, such as elevation in intracellular calcium ions.50 Levels of ATP and PCr at the end of ZF ischemia were significantly lower in hearts treated with 8SPT than in saline-treated hearts. Thus, endogenous adenosine preserves cellular energy stores during severe ischemia. However, we found no relation between total tissue ATP and PCr at the end of ischemia and recovery of function.

The agent 8SPT blocks adenosine A1 and A2 receptors relatively equipotently.27 Because of the polar sulfophenyl group, 8SPT does not cross the myocyte plasma membrane. Hence, it does not inhibit cAMP phosphodiesterase activity or interfere with release of adenosine from myocytes. We have previously examined the dose-response characteristics and duration of 8SPT in this preparation and shown that the concentration used gives complete blockade of adenosine receptors throughout the experimental protocol.13 Thus, lack of effect of 8SPT is not due to insufficient blockade of adenosine receptors. The use of neonatal hearts can be of importance. These hearts have greater intrinsic glycolytic capacity,51 and release of adenosine might be lower because of lower activity of the 5'-nucleotidase25 26 and preferential deamination of AMP to IMP instead of dephosphorylation to form adenosine.24

Effect of Elevating Endogenous Levels of Adenosine: Possible Mechanisms of Action
Even though endogenous adenosine produced during ischemia does not seem to affect functional recovery, we show that elevating endogenous adenosine levels by draflazine improves functional recovery after both LF and ZF ischemia. This indicates that nonprotective levels of adenosine can be augmented to elicit protection. To the best of our knowledge, the present study is the first to show that elevating endogenous adenosine is protective in LF conditions as well. This is not obvious because there are great differences between LF and ZF ischemia with regard to accumulation of metabolites and ions and formation of free oxygen radicals upon reperfusion.38 Also, the amount of adenosine produced during ischemia depends on the degree of reduction in flow.8 Improved functional recovery after ZF ischemia has been shown after treatment with nucleoside transport inhibitors or inhibitors of adenosine deaminase during ischemia,32 33 34 52 53 54 55 56 57 but not in one study in isolated whole-blood–perfused rabbit hearts.37

Release of CK after ZF ischemia was reduced after treatment with draflazine. Reduction in infarct size has previously been shown after treatment with the nucleoside transporter inhibitors R7523128 29 and S-(p-nitrobenzyl)-6-thioinosine30 and inhibitors of adenosine deaminase,31 with one exception.36 To the best of our knowledge, the approach of elevating endogenous levels of adenosine has not previously been tested in neonatal hearts, but it has been shown to be protective against cerebral infarction in newborn rats.58

Even though endogenous adenosine is not responsible for downregulation of mechanical function during LF ischemia,10 11 12 13 14 15 our results show that when endogenous adenosine is augmented, mechanical function is further reduced. The negative chronotropic and inotropic effects are probably mediated by A1 receptors, which also antagonize ß-adrenergic actions.59 In parallel with reduced mechanical function during ischemia, draflazine-treated hearts had reduced MO2 and reduced signs of anaerobic metabolism. Draflazine is a nucleoside transport inhibitor and binds with high affinity to the nucleoside transporter in cell membranes of endothelial cells, erythrocytes, and pericytes. This inhibits cellular uptake of adenosine and other nucleosides and prevents intracellular degradation and transport across the endothelium.9 Thus, endogenous adenosine accumulates in the interstitial space, and the intravascular level also increases.9 Unlike dipyridamole, it does not affect the phosphodiesterase activity or prostacyclin formation. Biopsies at the end of LF and ZF ischemia confirmed higher levels of adenosine in draflazine-treated hearts than in both other groups. Because draflazine has been shown to be devoid of effects other than nucleoside transport inhibition both in vivo and in vitro,39 its effects are due to increased myocardial adenosine levels.

Adenosine can exert protective effects during ischemia as well as during reperfusion. Activation of A1 receptors on the myocyte seems most important during ischemia,1 mediating negative chronotropic and inotropic effects. During reperfusion, A2-mediated vasodilatation and inhibition of activated blood cells seem to be most important.1 In our study, these actions are probably of minor importance. Lack of blood elements other than erythrocytes eliminates effects on neutrophils and platelets. Flow-controlled perfusion reduces the importance of vasodilatation, although an effect on distribution might exist during LF ischemia and during reperfusion. Nucleoside transport inhibition leads to reduced formation of substrates for xanthine oxidase, which will reduce formation of harmful free oxygen radicals during reperfusion.57 This effect is also of minor importance, because porcine myocardium, like human myocardium, has no detectable xanthine oxidase.60 Other protective effects of elevated adenosine levels might involve reduced lipid peroxidation, reduced damage by free oxygen radicals,1 or altered glucose metabolism.15 49 50 61

We observed almost no increase in diastolic stiffness during ZF ischemia in draflazine-treated hearts. Because draflazine also altered function and metabolism during LF ischemia, this indicates that the protective effects of elevated adenosine levels are at least partly exerted during ischemia. A1 receptor activation may inhibit calcium overload50 through opening of ATP-sensitive potassium channels62 and also antagonize adrenergic effects.59 These mechanisms might contribute to the reduced ischemic contracture in draflazine-treated hearts. At the end of ZF ischemia, the declines in both ATP and PCr were similar in control hearts and hearts treated with draflazine. However, at the end of reperfusion after ZF ischemia, draflazine-treated hearts showed significantly higher levels of both metabolites compared with control hearts. Thus, elevated endogenous adenosine during severe ischemia seems to have beneficial effects both on recovery of function and generation of high-energy phosphates during reperfusion.63

Conclusions
Our results show that endogenous adenosine produced during LF and ZF ischemia does not significantly affect functional recovery or cell necrosis in neonatal porcine hearts. However, elevating adenosine levels by the nucleoside transport inhibitor draflazine improves functional recovery and prevents cell necrosis. This indicates that nonprotective levels of adenosine can be augmented to elicit protection if degradation of adenosine is inhibited. In treatment of patients with acute myocardial ischemia, increased endogenous adenosine levels may extend the time window for successful reperfusion. This approach provides a time- and site-specific therapy that minimizes unwanted systemic effects.


*    Selected Abbreviations and Acronyms
 
AV = arteriovenous
C1 = control measurement before ischemia just before administration of pharmacological agents
C2 = control measurement just before ischemia
CK = creatine kinase
HR = heart rate
KH = Krebs-Henseleit
LF = low-flow
LV = left ventricular
LVEDP = left ventricular end-diastolic pressure
LVSP = left ventricular systolic pressure
LVSP10 = LVSP at LVEDP=10 mm Hg
PCr = phosphocreatine
PP = perfusion pressure
sHR = spontaneous heart rate
8SPT = 8-sulfophenyltheophylline
ZF = zero-flow


*    Acknowledgments
 
This study was supported by the University of Oslo, Anders Jahre's Fund for Promotion of Science, Professor Carl Semb's Medical Research Fund, The Lærdal Foundation for Acute Medicine, and The Norwegian Air Ambulance Foundation. The authors acknowledge the technical support of Hilde Dishington, Unni Henriksen, Mette Ree Holte, Severin Leraand, Thea Sandsbråthen, Sissel Skarra, and Turid Verpe. Analysis of CK was kindly offered by Petter Urdal at Department of Clinical Chemistry, Ullevål Hospital. Special thanks to Morten Eriksen for skilled assistance throughout the experiments.


*    Footnotes
 
Reprint requests to Dr Hilchen T. Sommerschild, Institute for Experimental Medical Research, Ullevål Hospital, N-0407 Oslo, Norway.

Received February 26, 1997; revision received June 3, 1997; accepted June 14, 1997.


*    References
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  1. Hori M, Kitakaze M. Adenosine, the heart, and coronary circulation. Hypertension. 1991;18:565-574.[Abstract/Free Full Text]
  2. Babitt DG, Virmani R, Forman MB. Intracoronary adenosine administered after reperfusion limits vascular injury after prolonged ischemia in the canine model. Circulation. 1989;80:1388-1399.[Abstract/Free Full Text]
  3. Sekili S, Jeroudi O, Tang X-L, Zughaib M, Sun J-Z, Bolli R. Effect of adenosine on myocardial `stunning' in the dog. Circ Res. 1995;76:82-94.[Abstract/Free Full Text]
  4. Finegan BA, Lopaschuk GD, Coulson CS, Clanahan AS. Adenosine alters glucose use during ischemia and reperfusion in isolated rat hearts. Circulation. 1993;87:900-908.[Abstract/Free Full Text]
  5. Downey JM, Liu GS, Thornton JD. Adenosine and the anti-infarct effects of preconditioning. Cardiovasc Res. 1993;27:3-8.[Free Full Text]
  6. Kroll K, Kelm KMM, Buring K-F, Schrader J. Transendothelial transport and metabolism of adenosine and inosine in the intact rat aorta. Circ Res. 1989;64:1147-1157.[Abstract/Free Full Text]
  7. Bullough DA, Magill MJ, Mullane KM. Compartmentation of cardiac adenosine: importance of intravascular adenosine for cardioprotection. Circulation. 1995;92(suppl I):I-523.
  8. Delyani JA, Van Wylen DGL. Endocardial and epicardial interstitial purines and lactate during graded ischemia. Am J Physiol. 1994;266:H1019-H1026.[Abstract/Free Full Text]
  9. Van Belle H. Nucleoside transport inhibition: a therapeutic approach to cardioprotection via adenosine? Cardiovasc Res. 1993;27:68-76.[Medline] [Order article via Infotrieve]
  10. Schulz R, Rose J, Post H, Heusch G. Regional short-term myocardial hibernation in swine does not involve endogenous adenosine or KATP channels. Am J Physiol. 1995;268:H2294-H2301.[Abstract/Free Full Text]
  11. Minamino T, Kitakaze M, Morioka T, Node K, Shinozaki Y, Chujo M, Mori H, Takeda H, Inoue M, Hori M, Kamada T. Bidirectional effects of aminophylline on myocardial ischemia. Circulation. 1995;92:1254-1260.[Abstract/Free Full Text]
  12. Angello DA, Headrick JP, Coddington NM, Berne RM. Adenosine antagonism decreases metabolic but not functional recovery from ischemia. Am J Physiol. 1991;260:H193-H200.[Abstract/Free Full Text]
  13. Offstad J, Kirkebøen KA, Ilebekk A, Downing SE. ATP-gated potassium channels in acute hibernation and reperfusion. Cardiovasc Res. 1994;28:872-880.[Abstract/Free Full Text]
  14. Gao Z-P, Downey HF, Fan W-L, Mallet RT. Does interstitial adenosine mediate acute hibernation of guinea pig myocardium? Cardiovasc Res. 1995;29:796-804.[Medline] [Order article via Infotrieve]
  15. Lasley RD, Mentzer RM Jr. Adenosine increases lactate release and delays onset of contracture during global low flow ischaemia. Cardiovasc Res. 1993;27:96-101.[Abstract/Free Full Text]
  16. Rynning SE, Brunvand H, Birkeland S, Hexeberg E, Grong K. Endogenous adenosine attenuates myocardial stunning by antiadrenergic effects exerted during ischemia and not during reperfusion. J Cardiovasc Pharmacol. 1995;25:432-439.[Medline] [Order article via Infotrieve]
  17. Bunch FT, Thornton J, Cohen MV, Downey JM. Adenosine is an endogenous protectant against stunning during repetitive ischemic episodes in the heart. Am Heart J. 1992;124:1440-1445.[Medline] [Order article via Infotrieve]
  18. Auchampach JA, Gross GJ. Adenosine A1 receptors, KATP channels, and ischemic preconditioning in dogs. Am J Physiol. 1993;264:H1327-H1336.[Abstract/Free Full Text]
  19. Liu GS, Thornton J, Van Winkle DM, Stanley AWH, Olsson RA, Downey JM. Protection against infarction afforded by preconditioning is mediated by A1 adenosine receptors in rabbit heart. Circulation. 1991;84:350-356.[Abstract/Free Full Text]
  20. Liu G, Richards SC, Olsson RA, Mullane K, Walsh RS, Downey JM. Evidence that the adenosine A3 receptor may mediate the protection afforded by preconditioning in the isolated rabbit heart. Cardiovasc Res. 1994;28:1057-1061.[Abstract/Free Full Text]
  21. Zhao ZQ, McGee S, Nakanishi K, Toombs CF, Johnston WE, Ashar MS, Vinten-Johansen J. Receptor-mediated cardioprotective effects of endogenous adenosine are exerted primarily during reperfusion after coronary occlusion in the rabbit. Circulation. 1993;88:709-719.[Abstract/Free Full Text]
  22. Toombs CF, McGee DS, Johnston WE, Vinten-Johansen J. Myocardial protective effects of adenosine: infarct size reduction with pretreatment and continued receptor stimulation during ischemia. Circulation. 1992;86:986-994.[Abstract/Free Full Text]
  23. Hammon JW Jr. Myocardial protection in the immature heart. Ann Thorac Surg. 1995;60:839-842.[Abstract/Free Full Text]
  24. Wegelin I, Pane G, Finelli C, Clo C, Zanfanti ML. Age-related changes of AMP breakdown in chicken heart. Comp Biochem Physiol. 1995;110A:27-31.
  25. Matherne GP, Ely SW, Headrick JP. Maturational differences in bioenergetic state and purine formation during `supply' and `demand' ischemia. J Mol Cell Cardiol. 1996;28:1143-1155.[Medline] [Order article via Infotrieve]
  26. Pridjian AK, Bove EL, Bolling SF, Childs KF, Brosamer KS, Lupinetti FM. Developmental differences in myocardial protection in response to 5-nucleotidase inhibition. J Thorac Cardiovasc Surg. 1994;107:520-526.[Abstract/Free Full Text]
  27. Daly JW, Padgett W, Shamim MT, Butts-Lamb P, Waters J. 1,3-Dialkyl-8-(p-sulfophenyl)xanthines: potent water-soluble antagonists for A1 and A2-adenosine receptors. J Med Chem. 1985;28:487-492.[Medline] [Order article via Infotrieve]
  28. Martin BJ, Lasley RD, Noble MA, Hegge JO, Mentzer RM Jr. Nucleoside transport inhibition with R75231 augments endogenous adenosine concentrations and reduces infarct size in swine. Circulation. 1995;92(suppl I):I-523.
  29. Martin BJ, Lasley RD, Mentzer RM Jr. Infarct size reduction with the nucleoside transport inhibitor R-75231 in swine. Am J Physiol. 1997;272:H1857-H1865.[Abstract/Free Full Text]
  30. Poucher SM, Brooks R, Pleeth RM, Conant AR, Collis MG. Myocardial infarction and purine transport inhibition in anaesthetised ferrets. Eur J Pharmacol. 1994;252:19-27.[Medline] [Order article via Infotrieve]
  31. Sandhu GS, Burrier AC, Janero DR. Adenosine deaminase inhibitors attenuate ischemic injury and preserve energy balance in isolated guinea pig heart. Am J Physiol. 1993;265:H1249-H1256.[Abstract/Free Full Text]
  32. Masuda M, Demeulemeester A, Chang-Chun C, Hendrikx M, Van Belle H, Flameng W. Cardioprotective effects of nucleoside transport inhibition in rabbit hearts: a role of endogenous adenosine. Ann Thorac Surg. 1991;52:1300-1305.[Abstract]
  33. Van Belle H, Goossens F, Wynants J. Biochemical and functional effects of nucleoside transport inhibition in the isolated cat heart. J Mol Cell Cardiol. 1989;21:797-805.[Medline] [Order article via Infotrieve]
  34. Zughaib ME, Abd-Elfattah AS, Jeroudi MO, Sun J-Z, Sekili S, Tang X-L, Bolli R. Augmentation of endogenous adenosine attenuates myocardial `stunning' independently of coronary flow or hemodynamic effects. Circulation. 1993;88:2359-2369.[Abstract/Free Full Text]
  35. Itoya M, Miura T, Sakamoto J, Urabe K, Iimura O. Nucleoside transport inhibitors enhance the infarct size-limiting effect of ischemic preconditioning. J Cardiovasc Pharmacol. 1994;24:846-852.[Medline] [Order article via Infotrieve]
  36. Silva PH, Dillon D, Van Wylen DGL. Adenosine deaminase inhibition augments interstitial adenosine but does not attenuate myocardial infarction. Cardiovasc Res. 1995;29:616-623.[Medline] [Order article via Infotrieve]
  37. Galinanes M, Qiu Y, Van Belle H, Hearse DJ. Metabolic and functional effects of the nucleoside transport inhibitor R75231 in the ischaemic and blood reperfused myocardium. Cardiovasc Res. 1993;27:90-95.[Medline] [Order article via Infotrieve]
  38. Triana JF, Li X-Y, Jamaluddin U, Thornby JI, Bolli R. Postischemic myocardial `stunning': identification of major differences between open chest and the conscious dog and evaluation of the oxygen radical hypothesis in the conscious dog. Circ Res. 1991;69:731-747.[Abstract/Free Full Text]
  39. Van Belle H, Ver Donck K, Verheyen W. Role of nucleoside transport inhibition and endogenous adenosine in prevention of catecholamine induced death in rabbits. Cardiovasc Res. 1993;27:111-115.[Medline] [Order article via Infotrieve]
  40. Downing SE, Chen V. Acute hibernation and reperfusion of the ischemic heart. Circulation. 1992;85:699-707.[Abstract/Free Full Text]
  41. Eisenhauer CL, Matsuda LS, Uyehara CFT. Normal physiologic values of neonatal pigs and the effects of isoflurane and pentobarbital anesthesia. Lab Anim Sci. 1994;44:245-252.[Medline] [Order article via Infotrieve]
  42. Rosenberg JC, Rush BF. An enzymatic spectrophotometric determination of pyruvic and lactic acid in blood. Clin Chem. 1966;12:299-307.[Abstract]
  43. Lowry OH, Passonneau JV. A Flexible System of Enzymatic Analysis. New York, NY: Academic Press; 1972:147-217.
  44. Sellevold OFM, Jynge P, Aarstad K. High performance liquid chromatography: a rapid isocratic method for determination of creatine compounds and adenine nucleotides in myocardial tissue. J Mol Cell Cardiol. 1986;18:517-527.[Medline] [Order article via Infotrieve]
  45. Van Belle H, Janssen PAJ. Comparative pharmacology of nucleoside transport inhibitors. Nucleosides Nucleotides. 1991;10:975-982.
  46. Offstad J, Kirkebøen KA, Sommerschild HT, Ilebekk A, Downing SE. Repetitive stretching during myocardial low-flow ischemia impairs contractile function in isolated piglet hearts. J Mol Cell Cardiol. 1995;27:A181. Abstract.
  47. Janier MF, Vanoverschelde J-LJ, Bergmann SR. Adenosine protects ischemic and reperfused myocardium by receptor-mediated mechanisms. Am J Physiol. 1993;264:H163-H170.[Abstract/Free Full Text]
  48. Lasley RD, Mentzer RM Jr. Adenosine improves recovery of postischemic myocardial function via an adenosine A1 receptor mechanism. Am J Physiol. 1992;263:H1460-H1465.[Abstract/Free Full Text]
  49. Fralix TA, Murphy E, London RE, Steenbergen C. Protective effects of adenosine in the perfused rat heart: changes in metabolism and intracellular ion homeostasis. Am J Physiol. 1993;264:C986-C994.[Abstract/Free Full Text]
  50. Barry WH, Peeters GA, Rasmussen CAF Jr, Cunningham MJ. Role of changes in (Ca2+)i in energy deprivation contracture. Circ Res. 1987;61:726-734.[Abstract/Free Full Text]
  51. Lopaschuk GD, Collins-Nakai RL, Itoi T. Developmental changes in energy substrate use by the heart. Cardiovasc Res. 1992;26:1172-1180.[Abstract/Free Full Text]
  52. McClanahan TB, Ignasiak DP, Martin BJ, Mertz TE, Gallagher KP. Effect of adenosine deaminase inhibition with pentostatin on myocardial stunning in dogs. Basic Res Cardiol. 1995;90:176-183.[Medline] [Order article via Infotrieve]
  53. Dorheim TA, Hoffman A, Van Wylen DGL, Mentzer RM Jr. Enhanced interstitial fluid adenosine attenuates myocardial stunning. Surgery. 1991;110:136-145.[Medline] [Order article via Infotrieve]
  54. Kirkebøen KA, Ilebekk A, Tønnessen T, Leistad E, Næss PA, Christensen G, Aksnes G. Cardiac contractile function following repetitive brief ischemia: effects of nucleoside transport inhibition. Am J Physiol. 1994;36:H57-H65.
  55. Abd-Elfattah AS, Ding M, Dyke CM, Wechsler AS. Protection of the stunned myocardium: selective nucleoside transport blocker administered after 20 minutes of ischemia augments recovery of ventricular function. Circulation. 1993;88(pt 2):II-336-II-343.
  56. Abd-Elfattah AS, Jessen ME, Wechsler AS. Nucleoside trapping during reperfusion prevents ventricular dysfunction, `stunning,' in absence of adenosine. J Thorac Cardiovasc Surg. 1994;108:269-278.[Abstract/Free Full Text]
  57. Abd-Elfattah AS, Jessen ME, Hanan SA, Tuchy G, Wechsler AS. Is adenosine 5'-triphosphate derangement or free-radical-mediated injury the major cause of ventricular dysfunction during reperfusion? Role of adenine nucleoside transport in myocardial reperfusion injury. Circulation. 1990;82(suppl IV):IV-341-IV-350.
  58. Gidday JM, Fitzgibbons JC, Shah AR, Kraujalis MJ, Park TS. Reduction in cerebral ischemic injury in the newborn rat by potentiation of endogenous adenosine. Pediatr Res. 1995;38:306-311.[Medline] [Order article via Infotrieve]
  59. Pelleg A, Belardinelli L. Cardiac electrophysiology and pharmacology of adenosine: basic and clinical aspects. Cardiovasc Res. 1993;27:54-61.[Free Full Text]
  60. de Jong JW, van der Meer P, Nieukoop AS, Huizer T, Stroeve RJ, Bos E. Xanthine oxidoreductase activity in perfused hearts of various species, including humans. Circ Res. 1990;67:770-773.[Abstract/Free Full Text]
  61. Wyatt DA, Edmunds MC, Rubio R, Berne RM, Lasley RD, Mentzer RM Jr. Adenosine stimulates glycolytic flux in isolated perfused rat hearts by A1-adenosine receptors. Am J Physiol. 1989;257:H1952-H1957.[Abstract/Free Full Text]
  62. Kirsch GE, Codina J, Birnbaumer L, Brown AM. Coupling of ATP-sensitive K+ channels to A1 receptors by G proteins in rat ventricular myocytes. Am J Physiol. 1990;259:H820-H826.[Abstract/Free Full Text]
  63. Neely JR, Grotyohann LW. Role of glycolytic products in damage to ischemic myocardium: dissociation between adenosine triphosphate levels and recovery of function of reperfused ischemic hearts. Circ Res. 1984;55:816-824.[Abstract/Free Full Text]



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