(Circulation. 1995;92:400-404.)
© 1995 American Heart Association, Inc.
Articles |
From the Departments of Cardiac Surgery (T.H., J.F., T.M., M.A.C., J.E.M.) and Cardiology (S.J.R.), Children's Hospital and Harvard Medical School, Boston, Mass.
| Abstract |
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Methods and Results We measured plasma ET-1 concentrations by
radioimmunoassay in isolated blood-perfused neonatal lamb hearts
before and after 2 hours of 10°C cardioplegic ischemia and
examined the effects of ET-1 and the endothelin-A (ET-A) receptor
antagonist BE-18257B on the postischemic
recovery of isolated hearts. ET-1 levels in coronary sinus
blood before ischemia and at 0 and 30 minutes of reperfusion in
8 control hearts were constant (2.2±1.2 fmol/L, 2.2±1.3 fmol/L,
and
2.5±1.0 fmol/L, respectively). In group 2 (n=6), 10 µmol/L
of
BE-18257B was given just before reperfusion. In group 3 (n=8), 10
pmol/L ET-1 was given just before the start of reperfusion. At 30
minutes of reperfusion, the ET-A antagonist hearts had
significantly greater recovery of LV systolic (positive dP/dt
and dP/dt at V10) and diastolic function (negative dP/dt),
coronary blood flow (CBF), and
M
O2 compared with controls
(P<.05). The ET-1 hearts showed significantly reduced
recovery of LV systolic (positive maximum and
volume-normalized dP/dt) and diastolic (negative
maximum dP/dt) function, CBF, and myocardial oxygen consumption
compared with controls (P<.05).
Conclusions These results, combined with prior studies, suggest that I/R causes reduced production of endogenous vasodilators (eg, nitric oxide), leaving unopposed the vasoconstriction that is caused by the continued presence of ET-1. This imbalance may contribute to I/R injury. ET-A receptor antagonists may be useful therapeutic agents in reducing the injury that results from I/R.
Key Words: endothelin ischemia reperfusion
| Introduction |
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ETs are thought to be involved in the pathogenesis of hypertension, heart failure, bronchial asthma, renal failure, and vasospasm.5 There are three ET isoforms (ET-1, ET-2, and ET-3), and two types of ET receptors have been reported, designated ET-A (selective for ET-1) and ET-B (nonselective with respect to isopeptides of the ET family).5 ET-A receptors are abundant in cardiovascular tissues and are also found on vascular smooth muscle cells that respond to ET-1 by contraction.5
In the present study, we used ET-1 and an ET-A receptor antagonist (BE-18257B, a cyclic pentapeptide6 ) in neonatal lamb hearts in an attempt to determine whether endogenous ET-1 is released into the coronary circulation during hypothermic myocardial ischemia/reperfusion and whether ET-1 has an influence on recovery of postischemic ventricular function.
| Methods |
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Measurements
LV function was measured during isovolumic
contraction by
stepwise inflation of the intraventricular balloon
as described previously.1 2 4 The
recovery of
systolic function was evaluated by measuring the maximum (max)
DP, positive (+) max LV dP/dt, peak DP at a constant balloon volume
(V10), and peak dP/dt at V10. V10 was defined as the balloon volume
required to produce an EDP of 10 mm Hg during baseline measurements.
To assess diastolic function, negative (-) max dP/dt and
EDP at V10 were measured. CBF was measured by use of an electromagnetic
flowmeter, which was connected to the venous cannula.
Arterial and venous blood were collected and
M
O2 was calculated from the
hemoglobin
concentration, oxygen content, and
saturation.1 2 4
Bioassay of Plasma ET-1
Coronary sinus blood samples were
collected after 20
minutes of normothermic bypass (baseline), at the start of
reperfusion (0 minutes), and again after 30 minutes of reperfusion in
eight control hearts. Plasma ET-1 levels were quantitated using a
commercially available ET-1, 21-specific radioimmunoassay system
(Amersham). Briefly, we collected sheep blood into tubes containing 7.5
mmol/L EDTA, and the samples were centrifuged at
2000g for 10 minutes at 4°C. The plasma was immediately
frozen at -20°C to minimize ET degradation. ET was extracted from 1
or 2 mL of acidified plasma using Amprep 500-mg C2 columns (Amersham).
After removal of solvent by centrifugal evaporation, samples were
reconstituted in 250-µL assay buffer (0.02 mol/L sodium borate, pH
7.4). Duplicate 100-µL sample aliquots plus 100-µL aliquots of
synthetic ET-1 of known concentration (for standardization) were
incubated with rabbit anti-endothelin antiserum for 4 hours at
4°C. A radioactive tracer, 125I ET-3, was added and
incubated for 16 to 24 hours at 4°C. The antibody-bound ET was
separated from ET by use of a donkey anti-rabbit antiserum coupled
to magnetic beads followed by magnetic separation (Amerlex-M Separator,
Amersham). The radioactive counts retained by the magnetic separator
were measured in a gamma scintillation counter (Packard Cobra
Auto-gamma). The concentration of ET-1 (in fmol/mL) was determined
by plotting the average of duplicate sample counts against the standard
curve of known ET-1 concentrations according to the manufacturer's
instructions.
Experimental Protocol
Baseline measurements were made after a
20-minute equilibrium
period. Then, the perfusate was cooled to 15°C. After 10
minutes of cooling (at myocardial temperature=15°C), coronary
perfusion was stopped and 20 mL/kg of cardioplegic solution was given,
followed by topical cooling (myocardial temperature was kept at
10°C). A second dose of cardioplegic solution (10 mL/kg) was given
after 60 minutes. The venous efferent during cardioplegia
administration was discarded. The cardioplegic solution consisted of
0.45% sodium chloride and 2.5% dextrose solution with 20 mEq/L of
potassium chloride and 6 mEq/L of sodium bicarbonate (pH=7.4 at
37°C,
osmolarity 360 mOsm/L). Reperfusion was begun with the
perfusate at room temperature (25°C), and the heart was
rewarmed by raising perfusate temperature to normothermia over
a 25-minute period. Mean coronary perfusion pressure was
maintained at 20 mm Hg for the first 5 minutes and raised to 40 mm Hg
for the second 5 minutes, then kept at 60 mm Hg until the end of the
experiment.1 2 High oxygencontent gas (95%
O2, 5% CO2) was supplied to the
oxygenator during the cooling phase and during the first 15 minutes of
reperfusion to mimic conditions of clinical cardiopulmonary
bypass. Thereafter, the gas was changed to normal oxygen levels (20%
O2, 5% CO2, 75%
N2).
Experimental Groups
Hearts were divided into three groups:
(1) In the control group
(n=8), there was no intervention during reperfusion; (2) In the ET-A
receptor antagonist group (n=6), the ET-A receptor
antagonist BE-18257B6 (purchased from Bachem)
was given just before reperfusion at a concentration of 10 µmol/L;
(3) In the ET-1 group (n=8), ET-1 (purchased from Bachem) was given
just before reperfusion at a concentration of 10 pmol/L.
Animals in this study received humane care in compliance with "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Sciences and published by the National Institutes of Health.
Statistics
All values are expressed as mean±SD and
were analyzed
by a statistical analysis system. One-way ANOVA and
repeated measures two-way ANOVA were used to compare the
differences in recovery between groups. Data were compared using
Student-Newman-Keuls test if ANOVA was significant. A value of
P<.05 was considered to be significant (NIH Publication No.
86-23, revised in 1985).
| Results |
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Baseline measurements (Table 2
). There were
no significant differences among the three groups in any of the
baseline hemodynamic data.
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LV function (Table 3
). The ET-A receptor
antagonist group had a significantly greater recovery of
+max dP/dt, dP/dt at V10, and -max dP/dt compared with both the
control group and the ET-1 group. The ET-1treated hearts had
significantly reduced recovery of LV systolic function indexes
including +max dP/dt and dP/dt at V10. The LV diastolic
function index (-max dP/dt) at 30 minutes of reperfusion was worse in
the ET-1 hearts compared with the control group.
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Coronary blood flow (Table 4
).
The ET-A receptor antagonist group had significantly
higher CBF than both the control group and the ET-1 group at 10 minutes
of reperfusion and thereafter. The ET-1 group had significantly lower
CBF than the control group at 25 minutes of reperfusion and
thereafter.
|
Oxygen consumption (M
O2)
(Table 5
). The ET-A receptor antagonist
group had significantly higher
M
O2
than the control group and the ET-1 group at 15 minutes of reperfusion.
At 30 minutes of reperfusion, the ET-1 hearts showed significantly
lower M
O2 than the control
group.
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Effects of ET-1 at normothermia without ischemia (Table 6
).
To assess the effect of ET-1 and the ET-A
receptor antagonist at normothermia without
ischemia, we infused 10 pmol/L ET-1 (n=4) and 10 µmol/L ET-A
receptor antagonist (n=2) in the same isolated heart model
without ischemia. The changes in LV function, CBF, and
M
O2 were examined 30
minutes later.
Data were compared with those in the control group at normothermia.
ET-1 (n=4) caused no significant change in LV function indexes except
that -max dP/dt declined. CBF and
M
O2
declined, but not significantly. Administration of the ET-A receptor
antagonist at normothermia (n=2) resulted in no significant
change in LV function and caused an insignificant (P>.05)
increase in CBF and
M
O2.
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| Discussion |
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O2. Administration of the
ET-A
receptor antagonist improved LV systolic and
diastolic function, CBF, and
M
O2. These data strongly
suggest that
ET-1 is involved in the pathogenesis of ischemia/reperfusion
injury in neonatal hearts, but also make it likely that other factors
are involved. ET-1 is a potent vasoconstrictive peptide, containing 21 amino acid residues, that is produced by endothelium and has multiple biological actions.7 Three ET isoforms (ET-1, ET-2, and ET-3) have been identified, and there appear to be few interspecies differences in these three ET isoforms.6 Two types of ET receptors have been reported. The ET-A receptor is selective for ET-1 and is located predominantly on vascular smooth muscle cells,2 whereas the ET-B receptor is nonselective with respect to isopeptides of the ET family. ET-A receptors are abundant in cardiovascular tissues including the kidney, adrenal glands, and the central nervous system.8 9 10 ET-B receptors are also found on the endothelium.2
Few reports have addressed the effects of ischemia and reperfusion on ET release. Increases in circulating levels of ET have been documented in states of severe cardiovascular stress, including cardiogenic shock,10 acute myocardial infarction,11 12 congestive heart failure,12 13 14 and essential hypertension.14 15 Brunner et al15 have reported that ET release was decreased during low-flow ischemia and then transiently increased during early reperfusion in isolated crystalloid-perfused rat hearts before returning to control levels. Our finding that postischemic ET-1 levels did not change significantly from preischemic levels suggests that little postischemic ET-1 release occurred, because most of the clearance of ET-1 is reported to occur in the kidney and lung.5 The plasma levels of ET-1 that we measured before ischemia (5.3 pg/mL) are on the same order of magnitude (0.3 to 1.7 pg/mL) as for human plasma in reports summarized by Nayler,5 but they are lower than reported in normal adult sheep.5
ET-1 administration before reperfusion resulted in significantly worse recovery of ventricular function and reduced CBF. ET-1 has been shown to induce dose-dependent coronary constriction and impaired diastolic relaxation in isolated rabbit hearts.16 Brunner et al15 found that administration of ET-2 at the onset of reperfusion initially resulted in improved aortic output (first 20 minutes), but thereafter aortic output was reduced compared with controls.
In isolated atria and ventricle preparation, ET does exert a positive
inotropic effect,5 17 18 19
but we did not find a significant
effect of either ET-1 or the ETA receptor antagonist on CBF
or systolic ventricular function 30 minutes after
administration to isolated hearts that were not subjected to
ischemia. Diastolic function was reduced, however
(Table 6
). Thus, in our experiments, whatever positive
inotropic
effects of ET-1 existed seemed to have been outweighed by its other
effects.
In contrast to the effects of ET-1, the administration of the ET-A receptor antagonist BE-18257B resulted in improved recovery of ventricular function and CBF in our experiments. To our knowledge, no prior experiments have been carried out in a model of hypothermic ischemia using this ET receptor antagonist. Watanabe et al20 found that an ET-A antibody did reduce myocardial infarct size in a rat model of normothermic myocardial ischemia and reperfusion. Thus, it appears that even if ET-1 levels are not elevated during reperfusion, blockade of ET-1 action is likely to be beneficial.
The results of our current experiments and prior experiments from our laboratory lead us to hypothesize that an imbalance of endothelium-derived vasodilators and vasoconstrictors exists after hypothermic ischemia and reperfusion, and this imbalance likely plays a significant role in ischemia/reperfusion injury. This hypothesis is based on several observations. We have demonstrated a decreased vasodilator response to intra-arterial acetylcholine1 2 in the isolated lamb heart model of hypothermic ischemia and reperfusion, a finding that implies a reduced ability of the endothelium to release EDRF (NO). We have also shown that provision of supplemental amounts of the EDRF precursor L-arginine results in improved postischemic ventricular function4 and partially restores the defect in the ability to release NO. Other investigators have provided evidence of increased sensitivity to ET after ischemia. Brunner et al15 have reported that ET-2 had a 30-times-greater potency after ischemia, and Nayler and coworkers5 21 have reported upregulation of ET receptors after ischemic or hypoxic insults. Our finding that postischemic CBF was reduced below preischemic levels also suggests that a relative vasoconstrictive influence was present. Finally, the finding that the ET-A receptor antagonist exerted beneficial effects in the absence of elevated ET-1 levels but did not have significant effects in the absence of ischemia suggests that after ischemia, naturally occurring antagonists to ET-1 are missing or are present in lower concentrations compared with preischemia. It is also noteworthy that EDRF normally inhibits the release of ET-122 23 and that ET normally stimulates the release of EDRF.24 It seems reasonable to hypothesize that the unopposed vasoconstrictor effect of ET-1 in a vascular bed, which may be more sensitive to its effects, could result in reduced postischemic CBF, which would in turn limit the postischemic recovery of the heart.
An alternative mechanism by which an ET-1/EDRF imbalance could reduce postischemic recovery is suggested by the recent observation that ET-1 increases neutrophil adhesion to endothelial cells by inducing leukocyte integrin expression.25 Since EDRF has been shown to inhibit the expression of endothelial adhesion molecules26 and to inhibit neutrophil-endothelial adhesion,27 an imbalance of ET-1 and EDRF could also enhance myocardial injury postischemia/reperfusion through accumulation of activated neutrophils in the coronary circulation.
These conclusions are limited by the fact that experiments were carried out in the isolated heart, although this model has the advantage of being free of the neural and hormonal influences that would be present in a whole-animal preparation. In addition, this model does have the advantage of being similar to the conditions of an extracorporeal bypass circuit and hypothermia, under which ischemia is usually induced during cardiac surgery. Additional studies in the whole animal will be necessary and are planned.
In summary, the results of the present study combined with findings in prior studies suggest that ischemia/reperfusion causes reduced production of endogenous vasodilators (eg, EDRF or NO), which consequently do not offset the vasoconstriction caused by the continued presence of ET-1. This imbalance may contribute to ischemia/reperfusion injury. Therefore, ET-A receptor antagonists may be useful therapeutic agents in ischemia/reperfusion.
| Selected Abbreviations and Acronyms |
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| Acknowledgments |
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| Footnotes |
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| References |
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2. Sawatari K, Kadoba K, Berger KA, Daich JA, Mayer JE Jr. Influence of initial reperfusion pressure after hypothermic cardioplegia on endothelial modulation of coronary tone in neonatal lambs: impaired coronary vasodilation response to acetylcholine. J Thorac Cardiovasc Surg. 1991;101:777-782. [Abstract]
3. Luscher TF, Boulanger CM, Yang Z, Noll G, Dohi Y. Interactions between endothelium-derived relaxing and contracting factors in health and cardiovascular disease. Circulation. 1993;87(suppl V):V-36-V-43.
4.
Hiramatsu T, Forbess JM, Miura T, Mayer JE Jr.
Effects of L-arginine and L-NAME on
recovery of neonatal lamb hearts after cold cardioplegic
ischemia: evidence for an important role for
endothelial production of nitric oxide.
J Thorac Cardiovasc Surg. 1995;109:81-87.
5. Nayler WG. The Endothelins. Berlin, Germany: Springer-Verlag; 1990:1-188.
6. Ihara M, Noguchi K, Saeki T, Fuluroda T, Tsuchida S, Kimura S, Fukami T, Ishikawa K, Kishikibe M, Yano M. Biological profiles of highly potent novel endothelin antagonists selective for the ETA receptor. Life Sci. 1991;50:247-255.
7. Yanagisawa M, Kurihara H, Tomobe Y, Kobayashi M, Mitsui Y, Yazaki Y, Goto K, Masaki T. A novel potent vasoconstrictor peptide produced by vascular endothelial cells. Nature. 1988;3321:411-415.
8. Arai H, Hori S, Aramori I, Ohkubo H, Nakanishi S. Cloning and expression of a cDNA encoding an endothelin receptor. Nature. 1990;348:730-732. [Medline] [Order article via Infotrieve]
9. Sakurai T, Yanagisawa M, Yakuwa Y, Miyazaki H, Kimura S, Goto K, Masaki T. Cloning of a cDNA encoding a non-isopeptide-selective subtype of the endothelin receptor. Nature. 1990;348:732-735. [Medline] [Order article via Infotrieve]
10. Cernacek P, Stewart DJ. Immunoreactive endothelin in human plasma: marked elevations in patients in cardiogenic shock. Biochem Biophys Res Commun. 1989;161:562-567. [Medline] [Order article via Infotrieve]
11. Miyauchi T, Yanagisawa M, Tomizawa T, Sugishita Y, Suzuki N, Fujino M, Ajiaska R, Goto K, Masaki T. Increased plasma concentrations of endothelin-1 and big endothelin-1 in acute myocardial infarction. Lancet. 1989;2:53-54. [Medline] [Order article via Infotrieve]
12.
Cavero PG, Miller WL, Heublein DM, Marguilies KB,
Burnett JC Jr. Endothelin in experimental congestive heart
failure in the anesthetized dog. Am J
Physiol. 1990;259:F312-F317.
13.
Marguilies KB, Hildebrand FL Jr, Lerman A, Perrela MA,
Burnett JC Jr. Increased endothelin in experimental heart
failure. Circulation. 1990;82:2226-2230.
14. Saigo Y, Nakao K, Mukoyama M, Imura H. Increased plasma endothelin level in patients with essential hypertension. N Engl J Med. 1990;322:205. Letter. [Medline] [Order article via Infotrieve]
15. Brunner F, du Toit E, Opie LH. Endothelin release during ischaemia and reperfusion of isolated perfused rat hearts. J Mol Cell Cardiol. 1992;24:1291-1305. [Medline] [Order article via Infotrieve]
16.
Karwatowski-Prokopczuk E, Wennmalm A. Effects of
endothelin on coronary flow, mechanical performance,
oxygen uptake, and formation of purines and on outflow of prostacyclin
in the isolated rabbit heart. Circ Res. 1990;66:46-54.
17.
Ishikawa T, Yanagisawa M, Kimura S, Goto K, Masaki T.
Positive inotropic action of novel vasoconstrictor peptide
endothelin on guinea pig atria. Am J Physiol. 1988;255:H970-H973.
18.
Goetz KL, Wang BC, Nadwed JB, Zhu JL, Leadley RJ Jr.
Cardiovascular, renal, and endocrine responses
to intravenous endothelin in conscious dogs.
Am J Physiol. 1988;255:R1064-R1068.
19. Simmon MS, Dunn MJ. Cellular signaling by peptides of the endothelin gene family. FASEB J. 1990;4:3989-4000.
20.
Watanabe T, Suzuki N, Shimomoto N, Fujino M, Imada A.
Contribution of endogenous endothelin to the
extension of myocardial infarct size in rats.
Circ Res. 1991;69:370-377.
21. Liu J, Casley DJ, Nayler WG. Ischemia causes externalization of endothelin-1 binding sites in rat cardiac membranes. Biochem Biophys Res Commun. 1989;164:1220-1225. [Medline] [Order article via Infotrieve]
22. Boulanger C, Luscher TF. Release of endothelin from porcine aorta: inhibition by endothelium-derived nitric oxide. J Clin Invest. 1990;85:587-590.
23.
Luscher TF, Yang Z, Tschudi M, von Segesser L, Stulz P,
Boulanger C, Siebenmann R, Turina M, Buhler FR. Interactions
between endothelin-A and endothelium-derived
relaxing factor in human arteries and veins.
Circ Res. 1990;66:1088-1094.
24.
de Nucci G, Thomas R, D'Orleans-Juste P, Antunes
E, Walder C, Warner TD, Vane JR. Pressor effects of circulating
endothelin are limited by its removal in the pulmonary
circulation and by the release of prostacyclin and
endothelium-derived relaxing factor.
Proc Natl Acad Sci U S A. 1988;85:9797-9800.
25.
Lopez Farre A, Riesco A, Espinosa G, Digiuni E,
Cernadas MR, Alvarez V, Monton M, Rivas F, Gallego MJ, Egido J, Casado
S, Caramelo C. Effects of endothelin-1 on neutrophil adhesion to
endothelial cells and perfused heart.
Circulation. 1993;88:1166-1171.
26. De Caterina R, Shin WS, Liao JK, Libby P. Nitric oxide inhibits cytokine-induced expression of endothelial leukocyte adhesion molecules. Circulation. 1994;90(pt 2):I-29. Abstract.
27.
Kubeo P, Suzuki M, Granger N. Nitric oxide: an
endogenous modulator of leukocyte adhesion.
Proc Natl Acad Sci U S A. 1991;88:4651-4655.
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