Coronary and aortic vasoreactivity protection with endothelin receptor antagonist, bosentan, after ischemia and hypoxia in aged rats

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Abstract

This study investigated the effects of bosentan, a dual endothelin ETA and ETB receptor antagonist, during hypoxia–reoxygenation of senescent aorta and during ischemia–reperfusion of senescent heart. Isolated aortic rings and isolated hearts from adult and senescent rats were submitted, respectively, to hypoxia/reoxygenation (20/30 min) and to low-flow ischemia/reperfusion (45/30 min), without or with bosentan (10−5 M). In the aorta, bosentan treatment prevented the impairment of relaxation in response to acetylcholine after hypoxia–reoxygenation at both ages. In the heart, coronary flow recovery during reperfusion, which is lower in senescents than in adults (48% vs. 76% of baseline value, respectively; P<0.05) was fully prevented by bosentan. Prevention of endothelial dysfunction during reoxygenation of hypoxic aorta and of coronary vasoconstriction during reperfusion of ischemic heart with a dual endothelin ETA and ETB receptor antagonist suggests a role of endothelin in the vulnerability of aorta to hypoxia–reoxygenation, and of coronary arteries to ischemia–reperfusion, especially during aging.

Introduction

Endothelin is increased in different pathological states such as ischemia–reperfusion and hypoxia–reoxygenation, in animals Vitola et al., 1996, Brunner et al., 1997 as in humans (Krüger et al., 1997). Endothelin exerts a vasoconstrictor effect mediated by both ETA and ETB receptors Balwierczak, 1993, Hercule and Oyekan, 2000. Gene expression and release of endothelin are increased after myocardial ischemia Brunner et al., 1997, Vitola et al., 1996, leading to oxidative stress (Ishida et al., 1990) and coronary vasoconstriction (Hiller et al., 1997), as well as after hypoxia in endothelial cells (Li et al., 1994). In addition, both hypoxia and ischemia potentiate vasoconstriction in response to exogenous endothelin Douglas et al., 1991, Neubauer et al., 1991. Bosentan, a potent orally active non-peptide antagonist of endothelin ETA and ETB receptors (Clozel et al., 1994) reduces myocardial and coronary injury in both in vivo and ex vivo models of ischemia–reperfusion Wang et al., 1995a, Wang et al., 1995b, Li et al., 1995, Fraccarollo et al., 1997, limits hypoxic vasoconstriction in rat aorta (Pape et al., 1997) and has vasodilator effects in humans with coronary artery disease (Wenzel et al., 1998).

During aging, the vasomotricity of blood vessels is decreased and the endothelial layer is altered (Marin, 1995), leading to a decreased endothelium-dependent relaxation in response to acetylcholine in humans (Egashira et al., 1993) as well as in animals (Barton et al., 1997). In addition, the aged heart, characterized by a reduced coronary flow and perfusion reserve, has a higher vulnerability to myocardial ischemia and reperfusion Assayag et al., 1998, Hachamovitch et al., 1989. Finally, vasoconstriction, in response to endothelin, is potentiated during aging, especially after ischemia–reperfusion (Goodwin et al., 1999). However, beneficial effects of endothelin receptor antagonists on such coronary vasoconstriction during ischemia–reperfusion, as well as on blood vessels' vasoreactivity during hypoxia–reoxygenation, have never been investigated during aging.

The objective of the present study was to investigate whether, in senescence, bosentan exerts beneficial effects on (1) endothelial and smooth muscle injury of rat aorta after hypoxia–reoxygenation, using an isolated blood vessel preparation and on (2) coronary injury of rat heart after ischemia–reperfusion, using an isolated perfused heart model.

Section snippets

Animals and experimental groups

Adult (4-month-old) and senescent (24-month-old) male Wistar rats were obtained from IFFA CREDO (Lyon, France). The spontaneous mortality rate of the 24-month-old population was 50% Assayag et al., 1997, Assayag et al., 1998.

For isolated heart studies, 4- and 24-month-old rats were subdivided into two randomized subgroups submitted to ischemia–reperfusion without (4-mo-control, n=11- and 24-mo-control, n=9, respectively) or with (4-mo-bosentan, n=8 and 24-mo-bosentan n=11, respectively)

Baseline parameters of isolated heart and aortic rings

In isolated hearts, baseline parameters of coronary flow and active tension are reduced in 24-month-old groups as compared to those in 4-month-old groups (Table 1). In isolated aortic rings, the maximum contraction with phenylephrine was lower in 24-month-old than in 4-month-old groups, as well as maximum relaxation with acetylcholine and sodium nitroprusside (Table 1).

Coronary and myocardial function during ischemia–reperfusion: effects of bosentan

Reperfusion induced an impairment of coronary flow in ischemic hearts at both ages (Fig. 1) but this impairment was greater in

Discussion

This study showed that coronary flow recovery during reperfusion following low-flow ischemia was less in senescent than in adult heart. This post-ischemic impairment of coronary perfusion was fully prevented by the administration of the endothelin receptor antagonist, bosentan, in adult as well as in senescent rats. In the aorta, bosentan treatment limited the hypoxic delayed contraction and, although it did not affect the reoxygenation-induced contraction, it fully prevented aortic endothelial

Acknowledgments

The authors thank Dr. Claude Sebban and Brigitte Decros for kindly providing senescent rats. This study was supported by grants from Fondation de France, Fédération Française de Cardiologie et Région Rhône-Alpes.

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