Time-Related Normalization of Maximal Coronary Flow in Isolated Perfused Hearts of Rats With Myocardial Infarction
Background In the present study, we investigated the time dependency and regional differences of the vascular adaptation of the myocardium after myocardial infarction (MI) in rats.
Methods and Results MI was induced by total occlusion of the left anterior descending coronary artery. Time-dependent adaptation of the coronary vasculature was determined by histological staining of endothelial cells and measurement of basal and maximal coronary flow at days 0, 4, 7, 21, 35, and 90 after surgery in isolated retrogradely perfused hearts of sham-operated and infarcted rats. Cardiac function was determined during anterograde perfusion. In a separate group of experiments, regional myocardial flow was measured with radiolabeled microspheres in sham-operated and infarcted hearts to determine local differences in adaptation. Basal coronary flow was completely normalized within 7 days, whereas maximal coronary flow was not normalized until 35 days after MI. Normal growth, as observed in sham-operated hearts, resulted in a parallel increase in coronary flow and tissue mass from day 7 to 35 after surgery. In contrast, the increase in coronary flow was lower than the hypertrophic response in the right ventricles and septa of infarcted hearts, whereas a parallel increase in tissue mass and coronary flow was observed in the left ventricles of these hearts. These functional data were supported by structural data that showed the presence of numerous and dilated vessels, especially in the border zone of the infarcted and noninfarcted tissue.
Conclusions These observations demonstrate that vessel growth, predominantly in the region adjacent to the infarcted zone, results in complete normalization of coronary vasodilatory capacity within 35 days after MI.
Because the myocardium under physiological conditions is totally dependent on aerobic metabolism, an increase in myocardial oxygen consumption requires an increase in coronary blood flow. This so-called coronary flow reserve of the myocardium is age-related1 and, moreover, is altered in pathophysiological conditions. Preservation of depressed coronary flow reserve was observed, for instance, in myocardial hypertrophy caused by hypertension (pressure overload),1 2 3 4 whereas complete normalization of the coronary flow reserve was demonstrated in the rat within a few weeks after volume overload.2 Four weeks after MI, decreased maximal coronary flow and coronary flow reserve were observed in the surviving myocardium.5 The depressed coronary reserve was suggested to be related to both developed hypertrophy and elevated preload because minimal coronary resistance correlated with myocyte cross-sectional area and LV end-diastolic pressure.
Induction of MI by total occlusion of part of the coronary vasculature diminishes coronary flow substantially.6 Consequently, the blood supply to the ischemic area can be improved by dilatation of the remaining vessels and development of collateral vessels.7 8 9 In the acute phase, collateral flow can be achieved by recruitment of preexisting vessels; in the chronic phase, new vessels can be formed.7 8 9 On this basis, the acute response after MI diminishes the coronary flow reserve, whereas the chronic response results in a normalization of coronary flow reserve.10
The growth of coronary vessels usually is very slow in adult rats.11 Induction of vessel growth has been described in cardiac hypertrophy resulting from pressure overload, thyroxine, or anemia.10 11 12 The increased DNA synthesis in the surviving part of the ventricles after MI, as demonstrated by van Krimpen et al,13 is partly localized in endothelial cells.14 This suggests vascular growth after MI. Anversa et al6 demonstrated an inadequate adaptation of the capillary vasculature to hypertrophy in the surviving part of the myocardium at 40 days after MI as measured by diffusion distance and capillary surface area. Furthermore, Karam et al5 showed a sustained reduction of maximal coronary flow 4 weeks after the induction of MI, which suggests a remaining perfusion deficit in the myocardium.
Because the time-dependent adaptation of the coronary vasculature after MI is not completely understood, we investigated the effect of MI on coronary flow in time. Therefore, both basal and maximal flows were determined in isolated Langendorff-perfused rat hearts several times between 0 and 90 days after sham surgery or MI. Furthermore, the development of blood vessels in time was visualized by histological staining of endothelial cells. Having established a diminished and normalized maximal coronary flow after 7 and 35 days, respectively, we determined regional differences in coronary flow after MI with radiolabeled microspheres at these times after sham surgery or MI.
Male Wistar rats (Harlan-Winkelmann, Borchen, Germany) weighing 260 to 325 g were used. Rats had free access to standard food (Hope Farms) and tap water and were housed in groups of up to four rats. The experimental procedures were performed according to institutional guidelines and approved by the Ethical Committee for the Use of Experimental Animals of the University of Limburg (the Netherlands).
Surgery and Preparations
MI was induced by coronary artery ligation under pentobarbital anesthesia (60 mg/kg IP).15 16 Intraoperatively, the rat was respired with room air (60 strokes per minute; tidal volume, 3 mL) after the trachea was intubated. After thoracotomy in the fourth left intercostal space, the heart was exteriorized, and a 6-0 silk suture was passed under the LAD near the origin of the pulmonary artery. In sham-operated rats, the suture was looped through the myocardium next to the LAD. After the heart was returned to its normal position, the suture was tied. The ribs were pulled together with 3-0 silk, and the skin was sutured. Rats were allowed to recover for 4, 7, 14, 21, 35, or 90 days. For measurements during acute MI (t=0 days), the LAD was occluded during isolated heart perfusion.
Isolated Heart Perfusion
Isolated hearts were perfused as described by Snoeckx et al.17 Under pentobarbital anesthesia (60 mg/kg IP), hearts of MI and sham-operated rats were excised rapidly and immersed immediately in ice-chilled perfusion medium (see below). After removal of lung and fat tissue, hearts were connected to the aortic cannula of the perfusion system, and retrograde perfusion (Langendorff perfusion model) was started at a diastolic aortic pressure of 60 mm Hg. The left atrium also was connected to a cannula for anterograde perfusion (ejecting heart model) for cardiac function measurements.17 18
The hearts were perfused with a modified Krebs-Henseleit solution ([mmol/L] NaCl 130, KCl 5.6, CaCl2 2.2, MgCl2 1.2, NaH2PO4 1.2, NaHCO3 25.0, glucose 10.0, and pyruvate 5.0). The solution was maintained at 37°C, gassed with 95% O2 and 5% CO2 (Po2 >600 mm Hg) to obtain a pH of 7.4, and continuously filtered (1.2-μm Millipore filter) throughout the perfusion period. The hearts were paced at 5 Hz.
A catheter (PE-50) was inserted into the LV through the apex and connected to a pressure transducer (Gould Spectramed DTX+, Spectramed) to measure LV pressure. Aortic pressure was measured by a pressure transducer connected to the inflow of the aortic cannula. During retrograde perfusion, coronary flow was measured by an electromagnetic flow probe (Skalar) mounted in the aortic inflow tract. During anterograde perfusion, aortic flow was measured by the electromagnetic flow probe, whereas coronary flow was measured by collection of the coronary outflow in a graduated cylinder. CO was calculated as the sum of coronary flow and aortic flow. Except for CO, all hemodynamic variables were monitored continuously or calculated on-line by a computer.
Staining of Endothelial Cells of the Myocardium
In separate groups of rats, endothelial cells were stained in paraffin-embedded sections of the myocardium of rats with MI (days 7, 14, 35, and 90). Under ether anesthesia, the hearts of rats with MI were arrested in diastole by injection of 2 mL of 0.1 mol/L CdCl2 into the inferior caval vein and perfused with a catheter in the abdominal aorta with PBS (pH 7.4) containing 0.5 mg/mL nitroprusside for 5 to 10 minutes at a pressure of ≈100 mm Hg. Thereafter, the hearts were perfusion-fixed for 10 minutes with 10% phosphate-buffered formalin (1:1 diluted in PBS) containing 0.5 mg/mL nitroprusside. The hearts were removed and stored in 10% phosphate-buffered formalin for 24 hours at room temperature. Subsequently, the hearts were cut into 4-mm transverse slices and embedded in paraffin.
To determine endothelial cells in the myocardium, 4-μm transverse sections were stained with the lectin GSI (Sigma Chemical Co), as described previously by Kuizinga et al.14 Therefore, the sections were dewaxed and rehydrated, and endogenous peroxidase was inhibited by methanol/H2O2 (0.3%) for 15 minutes. The sections were incubated overnight with the biotinylated lectin GSI (1:100) at room temperature; then the sections were incubated with the alkaline phosphatase–conjugated biotine-avidine complex (1:200, Dakopatts) for 30 minutes at room temperature and developed with fast blue BB (Sigma Chemical Co).
Retrograde Perfusion Studies
The hearts were prepared for retrograde perfusion at day 4, 7, 21, 35, or 90 after sham surgery or induction of MI. After equilibration of the isolated hearts, basal values of coronary flow were determined. Thereafter, maximal coronary vasodilatation was obtained by subsequent injections of 0.5 mL adenosine (1 mmol/L), nitroprusside (1 mmol/L), and adenosine plus nitroprusside (1 mmol/L each). At day 0, MI was induced acutely after equilibration of the perfused hearts. Basal and maximal values of coronary flow in acute MI were measured under steady state conditions (within 10 to 20 minutes of ligation of the LAD). Except at day 0, all hearts were subjected to anterograde perfusion after retrograde perfusion.
Anterograde Perfusion Studies
After retrograde perfusion the hearts were prepared for anterograde perfusion to measure cardiac function. Therefore, the hearts were exposed to different combinations of preload (5, 10, 15, and 20 mm Hg) and afterload (diastolic aortic pressure, 60, 100, and 140 mm Hg). Aortic flow, coronary flow, aortic pressure, and LV pressure were determined after stabilization. At the end of the experiments, the ventricles were weighed, and infarct size was determined (see below).
In separate groups, differences in regional distribution of coronary flow between days 7 and 35 after MI were determined with radiolabeled microspheres. Hearts were prepared for Langendorff perfusion 7 and 35 days after sham surgery or induction of MI. After equilibration of the isolated hearts, basal values of coronary flow were measured, and ≈5000 radiolabeled microspheres (141Ce or 103Ru 15 μm in diameter) per 1 g tissue were injected.19 After a single injection of 0.5 mL of adenosine plus nitroprusside (1 mmol/L each), maximal coronary flow was measured, followed by injection of ≈5000 radiolabeled microspheres (103Ru or 141Ce) per 1 g tissue. 141Ce and 103Ru were used in a randomized order.
At the end of the microspheres experiments, atria and adherent tissues were removed before the ventricles were quickly frozen (−20°C) and cut into transverse slices of 1 to 2 mm. Then all slices of sham-operated hearts were divided into RV, septum, and LV, whereas the slices of MI hearts were stained with nitro blue tetrazolium20 to distinguish between infarcted and noninfarcted tissue. Infarct size was determined in the midventricular slice (see below). Thereafter, all slices were divided in RV, septum, center of MI, border zone (border of LV and MI), and the rest of the (surviving) LV. The atria (including adhesive tissues) and the different parts of the ventricles were weighed and counted for radioactivity (1282 Compu Gamma, LKB Wallac).21 Absolute flows in the different parts of the heart could be calculated from total basal and maximal coronary flow measured by the electromagnetic flow probe during perfusion. To compare coronary flow in hearts at 7 and 35 days after surgery, the flows in the different parts of the heart were normalized for the weight of the corresponding tissue parts.
Cautious isolation of the heart resulted in adherent tissue (eg, residuals of lung tissue and bronchi) that was difficult to remove from the atria after perfusion. The amount of adherent tissue varied in the different experimental groups (predominantly sham-operated versus MI; not quantified). Because the adherent tissue does not contribute to coronary flow, it will differentially underestimate the flow normalized for the corresponding weight in the atria and total heart. To avoid these problems, total ventricular flow was calculated out of total heart flow and atrial flow.
Measurement of Infarct Size
To measure infarct size, the hearts were cut into transverse slices of 1 to 2 mm, resulting in five to six slices. In the retrograde and anterograde perfusion studies, the midventricular slice was fixed with formalin and embedded in paraffin; then transverse sections (4 μm) were stained according to the modified AZAN technique.13 In the microspheres studies, the slices were stained with nitro blue tetrazolium20 ; then the midventricular slice was used for measurement of infarct size. Infarct size was determined by planimetry and expressed in percentage of LV circumference, calculated as the average of infarct sizes of endocardial and epicardial surfaces.22 23
The infarct size of hearts at day 0 (retrograde and anterograde studies) was not determined because both staining methods were not suitable for detection of infarcted area after acute MI.
Only hearts with infarct sizes >21% were used in the MI groups because smaller infarcts do not have detectable hemodynamic consequences in vivo.24
Data of time-related experiments were compared with values obtained at day 0 by one-way ANOVA and Dunnett’s test (retrograde perfusion studies) or compared between the time groups by one-way ANOVA and Bonferroni’s test (anterograde studies). Data of sham-operated and MI rats were compared by Student’s t test for unpaired observations (retrograde perfusion and microspheres studies) or by two-way ANOVA (anterograde studies). Data were expressed as mean±SEM. Differences were regarded to be statistically significant at P<.05.
Retrograde and Anterograde Perfusion Experiments
Hemodynamic values of sham-operated hearts during anterograde perfusion were comparable among the different times (Table 1⇓). CO was significantly reduced in hearts with MI in relation to sham-operated hearts at day 35 after surgery, independent of preload and afterload (Fig 1⇓). Comparable differences between sham-operated and MI hearts were found at days 4, 7, 21, and 90 after surgery (data not shown). These observations demonstrate that the hearts with MI can attain normal CO levels only at relatively high preload and low afterload levels, suggesting mechanical failure of the hearts.
Because of normal growth, both body weight and total ventricular weight increased over time in sham-operated rats (Table 2⇓). At all times, body weight was lower in MI compared with sham-operated rats. Differences were significant only at days 0, 7, and 90 and were not due to differences in weight before surgery except for day 0 (data not shown). Total ventricular weight was greater in MI than in sham-operated rats (significant at day 90). If we take into account that >40% of the LV was infarcted and thus atrophic, the greater increase in total ventricular weight over time suggests the development of hypertrophy in the noninfarcted part of the MI hearts. We did not apply the ratio of ventricular weight to body weight as an indicator for development of hypertrophy over time because formation of peripheral and cardiac edema can influence ventricular weight and body weight differently over time. Furthermore, the development of both atrophy and hypertrophy in hearts with MI implies that normalization of coronary flow for total ventricular weight of both sham-operated and MI hearts was not appropriate in these experiments.
As Fig 2A⇓ shows, basal coronary flow of sham-operated rats increased over time. This increase parallels the increase in total ventricular weight (Table 2⇑). Ligation of the LAD during perfusion (day 0) resulted in a reduction of basal coronary flow by ≈25% (before, 14.0±0.8 mL/min; after, 10.8±0.8 mL/min). Within 7 days, basal coronary flow in MI hearts was normalized compared with sham-operated hearts (sham, 13.6±0.6 mL/min; MI, 14.2±0.9 mL/min). At that time, maximal coronary flow was still significantly lower in MI than in sham-operated hearts (Fig 2B⇓). Complete normalization of the maximal coronary flow was achieved after 35 days (sham, 21.9±1.2 mL/min; MI, 21.2±0.6 mL/min), whereas at day 90, maximal coronary flow was significantly higher than in sham-operated hearts (sham, 24.1±0.5 mL/min; MI, 25.9±0.7 mL/min).
The increases in total ventricular weight and maximal regional myocardial flow of sham-operated hearts from day 7 to 35 were similar to those found in the retrograde perfusion experiments (Tables 2⇑ and 3⇓). In contrast to the findings in the retrograde perfusion experiments, total ventricular weight of MI hearts at day 35 was significantly higher compared with sham-operated hearts. Furthermore, maximal regional myocardial flow in MI hearts at day 35 was still slightly but significantly lower than in sham-operated hearts. The latter, however, was not due to a lower flow in the MI hearts in the present experiment but to a relatively high flow in the sham-operated hearts.
To relate maximal regional myocardial flow values between groups of sham-operated hearts and between groups of MI hearts, the flows in RVs, septa, and different LV sections were corrected for the corresponding tissue weights (Fig 3A⇓ and 3B⇓). In sham-operated hearts, the maximal flows of all sections were comparable between days 7 and 35 (Fig 3A⇓). In contrast, the maximal flows in RVs and septa of MI hearts were significantly lower at day 35 compared with day 7 (RV, 21.2±1.2 and 27.5±2.2 mL·min−1·g−1; septum, 19.8±0.8 and 25.5±2.4 mL·min−1·g−1, respectively), whereas maximal flows in the different LV sections were comparable between days 7 and 35 (Fig 3B⇓). Regional distribution of coronary flow under basal conditions was similar to that after maximal dilatation (data not shown).
Fig 4⇓ shows the relation between the increase in absolute flow and weight at day 35 compared with day 7 in the RV, septum, and LV (in MI hearts, the rest of the surviving LV). Therefore, the mean values of the absolute flow or weight of the RV, septum, and LV at day 35 were subtracted from the mean values of the absolute flow or weight of the corresponding parts at day 7. The increase in flow and weight in the (surviving) LV in MI hearts was comparable to that during normal growth. In contrast to what is observed in sham-operated hearts, the increase in weight in the RV and septum in MI hearts was not paralleled by a comparable increase in flow.
Fig 5⇓ illustrates the presence of endothelial cells in the proximity of the infarcted area at different times after MI. A regular distribution of capillaries around cardiomyocytes can be observed in the noninfarcted area (Fig 5A⇓). The abundance and dilatation of blood vessels in the infarcted area of the myocardium increase in time, as demonstrated clearly in Fig 5B⇓ through 5E. Within 7 days, GSI-stained vessels are present without preferential orientation in the granulation tissue in the border zone of the infarcted and noninfarcted area. From day 14 to 90 after MI surgery, the blood vessels are oriented parallel to the scar tissue at both the epicardial and endocardial sites of the scar tissue.
To investigate the time dependency of the development of collateral flow by recruitment of preexisting vessels or development of new vessels after MI, we examined acute and chronic effects of MI on basal and maximal coronary flow in isolated perfused rat hearts. Induction of MI resulted acutely in a reduction in basal and maximal coronary flow. The basal coronary flow in MI hearts was completely normalized within 1 week, whereas the maximal coronary flow was normalized after 5 weeks after MI. This normalization of maximal coronary flow in MI hearts was regionally dependent. The increase in myocardial flow lagged behind the tissue growth in the RV and septa of MI hearts, whereas a parallel increase in flow and weight was observed in the surviving LV. These observations suggest that the normalization of the maximal coronary flow is due predominantly to an increase in flow in the proximity of the infarcted area. This is supported histologically by the presence of numerous and dilated vessels in the infarcted region of MI hearts in time.
Normalization of coronary flow for total heart weight in both sham-operated and MI hearts is not appropriate in the present experiments because of a thinning of the infarcted area (atrophic response) and hypertrophy of the surviving myocytes.25 26 27 The latter process explains the observed significant difference between ventricular weight of sham-operated and MI hearts at day 90 (Table 2⇑). When we take into account that >40% of the LV is infarcted and becomes atrophic,26 the surviving part of the hearts must also be hypertrophic at days 21 and 35. In contrast to MI hearts, the increase in coronary flow in sham-operated hearts observed in time results only from normal growth of the ventricles because the ratio of coronary flow to heart weight of sham-operated hearts is similar in time (data not shown).
Basal Coronary Flow
Induction of MI by total occlusion of the LAD results in an acute decrease in both basal and maximal coronary flow. The basal coronary flow in MI hearts increases to a preocclusive level within 4 days, is comparable between MI and sham-operated hearts from day 7 to 35, and is significantly elevated in MI hearts 90 days after MI. An elevated basal coronary flow also was observed in in vivo experiments,5 although the elevation was already observed 4 weeks after MI surgery. A possible explanation for such an increase in basal coronary flow is dilatation of the remaining coronary vessels that supply the ischemic (border) zone. Furthermore, a rise in basal coronary flow may be due to a higher oxygen demand of the surviving myocardium of infarcted hearts because the efficiency of the oxygen consumption is lower after MI. The latter has been demonstrated in in vivo experiments in which a normal oxygen consumption in MI hearts (approximated by the product of arterial pressure and heart rate) resulted in decreased stroke work.24 The time discrepancy between the in vivo5 and the present experiments may be due to differences in oxygen demand or the presence of neurohumoral regulation mechanisms in vivo.
Maximal Coronary Flow
The maximal coronary flow obtained with a combination of adenosine and nitroprusside was used in this study as a measure for the total amount of perfusable coronary vessels.28 The observed normalization of maximal coronary flow within 35 days in MI hearts suggests vessel growth associated not only with normal tissue growth but also with the developed hypertrophy (see above) or with the processes in the infarcted part of the myocardium. In vivo, maximal coronary blood flow also was depressed in infarcted hearts 4 weeks after surgery.5 However, a decreased afterload in MI rats in vivo can be responsible for the depressed maximal coronary flow. Although we observed a normalized maximal coronary flow, the adaptation of the capillary vasculature seems to be inadequate, as suggested by a lower capillary surface area and an elevated diffusion distance in the surviving LV of hearts with both small and large infarctions 40 days after surgery.6 The discrepancy between functional and structural parameters for adaptation in MI hearts can be explained by regional differences in vascular adaptation because the structural parameters were measured only in the surviving LV.6 An enhanced response of (new) coronary blood vessels to vasodilating substances also can be an explanation because we observed the presence of dilated blood vessels in the proximity of the infarcted area (Fig 5⇑).
Regional Myocardial Flow and Structural Evidence
Adaptation of myocardial tissue mass after MI can differ regionally because a combination of normal growth and hypertrophy occurs in the surviving parts of the myocardium.6 29 Furthermore, development of scar tissue and scar contraction results in shrinkage of the infarcted part of the myocardium. Ultimately, these processes may result in regional differences in adaptation of vessel growth. In the present experiments, the normal relation between tissue growth and the increase in coronary flow is demonstrated in sham-operated hearts in which the tissue growth in all parts of the heart is paralleled by an increase in coronary flow. In MI hearts, however, tissue growth is not paralleled by a comparable increase in coronary flow in the RV and septum. This result is in agreement with observations in cardiac hypertrophy in hypertension in which the increase in flow or vascular density is not proportional to the hypertrophic growth response,1 10 11 30 although the degree of the increase in coronary flow seems to depend on the duration of hypertension.31 32 In contrast to the RV and septum, the increase in coronary flow in the surviving part of the LV of MI hearts compensates completely for the increase in tissue growth. Assuming that the hypertrophic response to stretch is comparable in septum and surviving LV, the contradiction between the increases in flow and weight in surviving LV and septum cannot be explained by a smaller increase in weight in the surviving LV. This suggests that a greater stimulus for vessel growth is responsible for the parallel increase in flow and weight in the surviving LV. That the development of new vessels in the LV is indeed responsible for the parallel increase in tissue growth and coronary flow is supported by the presence of numerous and dilated vessels in the proximity of the infarcted area (Fig 5⇑). The regionally dependent adaptation of vessel growth after MI may be related to regional differences in stimuli for vessel growth, possibly because of differences in metabolic demand or neurohumoral regulation mechanisms.
The present experiments demonstrate a region- and time-dependent adaptation of the coronary vascular bed to chronic MI. The increase in coronary flow in the proximity of the infarcted area, which is associated with an increase in vessel number, seems to be predominantly responsible for the normalization of the maximal coronary flow in infarcted hearts 5 weeks after surgery.
Selected Abbreviations and Acronyms
|GSI||=||Griffonia Simplicifolia I|
|LAD||=||left anterior descending coronary artery|
This work was supported by grant 902-18-291 from the Dutch Heart Foundation and NWO (the Netherlands). We thank Richard N. Cornelussen, Peter J.A. Leenders, and Elsbeth A. Raes for expert technical assistance.
- Received November 22, 1994.
- Revision received March 29, 1995.
- Accepted August 29, 1995.
- Copyright © 1996 by American Heart Association
Vitullo JC, Penn MS, Rakunsan K, Wicker P. Effects of hypertension and aging on coronary arteriolar density. Hypertension. 1993;21:406-414.
Wåhlander H, Haraldsson B, Friberg P. Myocardial capillary diffusion capacity in rat hearts with cardiac hypertrophy due to pressure and volume overload. Am J Physiol. 1993;265:H61-H68.
Duncker DJ, Zhang J, Bache RJ. Coronary pressure-flow relation in left ventricular hypertrophy: importance of changes in back pressure versus changes in minimum resistance. Circ Res. 1993;72:579-587.
Karam R, Healy BP, Wicker P. Coronary reserve is depressed in postmyocardial infarction reactive cardiac hypertrophy. Circulation. 1990;81:238-246.
Anversa P, Beghi C, Kikkawa Y, Olivetti G. Myocardial infarction in rats: infarct size, myocyte hypertrophy, and capillary growth. Circ Res. 1986;58:26-37.
Hudlicka O, Brown M, Egginton S. Angiogenesis in skeletal and cardiac muscle. Physiol Rev. 1992;72:369-417.
Tomanek RJ. Capillary and pre-capillary coronary vascular growth during left ventricular hypertrophy. Can J Physiol Pharmacol. 1986;2:114-119.
Anversa P, Ricci R, Olivetti G. Coronary capillaries during normal and pathological growth. Can J Physiol Pharmacol. 1986;2:104-113.
Olivetti G, Lagrasta C, Quaini F, Ricci R, Moccia G, Capasso JM, Anversa P. Capillary growth in anemia-induced ventricular wall remodeling in the rat heart. Circ Res. 1989;65:1182-1192.
van Krimpen C, Smits JFM, Cleutjens JPM, Debets JJM, Schoemaker RG, Struyker Boudier HAJ, Bosman FT, Daemen MJAP. DNA synthesis in the non-infarcted cardiac interstitium after left coronary artery ligation in the rat: effects of captopril. J Mol Cell Cardiol. 1991;23:1245-1253.
Kuizinga MC, Cleutjens JPM, Smits JFM, Daemen MJAP. Griffonia Simplicifolia I (GSI): a suitable rat cardiac microvascular marker on paraffin embedded tissue. J Mol Cell Cardiol. 1992;24(suppl V):S57. Abstract.
Pfeffer MA, Pfeffer JM, Fishbein MC, Fletcher PJ, Sparado J, Kloner RA, Braunwald E. Myocardial infarct size and ventricular function in rats. Circ Res. 1979;44:503-512.
Lepràn I, Koltai M, Siegmund W, Szekeres L. Coronary artery ligation, early arrhythmias, and determination of the ischemic area in conscious rats. J Pharmacol Toxicol Methods. 1983;9:219-230.
Pfeffer JM, Pfeffer MA, Braunwald E. Influence of chronic captopril therapy on the infarcted left ventricle of the rat. Circ Res. 1985;57:84-95.
Anversa P, Li P, Zhang X, Olivetti G, Capasso JM. Ischaemic myocardial injury and ventricular remodelling. Cardiovasc Res. 1993;27:145-147.
Smits JFM, Daemen MJAP. Insights from animal models of myocardial infarction: do ACE inhibitors limit the structural response? Br Heart J. 1994;72(suppl):61-64.
Pfeffer MA, Braunwald E. Ventricular remodelling after myocardial infarction. Circulation. 1990;81:1161-1172.
Hoffman J. Maximal coronary flow and the concept of coronary vascular reserve. Circulation. 1984;70:153-159.
Capasso JM, Li P, Zhang X, Anversa P. Heterogeneity of ventricular remodeling after acute myocardial infarction in rats. Am J Physiol. 1992;262:H486-H495.
O’Keefe DD, Hoffman JIE, Cheitlin R, O’Neill MJ, Allard JR, Shapkin E. Coronary blood flow in experimental canine left ventricle hypertrophy. Circ Res. 1978;43:43-51.
Tomanek RJ, Schalk KA, Marcus ML, Harrison DG. Coronary angiogenesis during long-term hypertension and left ventricular hypertrophy in dogs. Circ Res. 1989;65:352-359.