Protective effects of 17beta-estradiol on post-ischemic cardiac dysfunction and norepinephrine overflow through the non-genomic estrogen receptor/nitric oxide-mediated pathway in the rat heart.

The present study was undertaken to examine the effect of acute treatment with 17ß-estradiol on post-ischemic cardiac dysfunction and norepinephrine overflow and its possible mechanisms. Male rat hearts were perfused with the Langendorff method and subjected to 40 min of global ischemia followed by 30 min of reperfusion. Each drug was perfused from 15 min before ischemia to 5 min after reperfusion. During reperfusion, 17ß-estradiol treatment showed significantly greater functional recovery of left ventricular developed pressure (LVDP), left ventricular end diastolic pressure (LVEDP), and dP/dt(max). Excessive norepinephrine release in coronary effluent from the post-ischemic heart was notably suppressed by treatment with 17ß-estradiol. These beneficial effects of 17ß-estradiol were not observed in the presence of the nitric oxide synthase inhibitor N(G)-nitro-l-arginine and estrogen receptor antagonist ICI 182,780 ((7α, 17ß)-7-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-triene-3,17-diol), respectively. When NO(2)/NO(3) levels in coronary effluents after the onset of reperfusion were measured, reverse-correlation relationships between NO(2)/NO(3) production and ischemia/reperfusion-induced cardiac dysfunction, as well as norepinephrine overflow were observed. These findings suggest that 17ß-estradiol exerts cardioprotective effects against ischemia/reperfusion-induced cardiac dysfunction, at least in part, by suppressing norepinephrine overflow, and that nitric oxide production via estrogen receptor activation plays a key role in this process.

Sex differences in postischemic cardiac dysfunction and norepinephrine overflow in rat heart: the role of estrogen against myocardial ischemia-reperfusion damage via an NO-mediated mechanism.

The purpose of this study is to elucidate the relationship between sex difference and norepinephrine (NE) release in the pathogenesis of myocardial ischemia/reperfusion (I/R) injury. Isolated male and female rat hearts were subjected to 40-minute global ischemia followed by 30-minute reperfusion. Compared with male hearts, I/R-induced cardiac dysfunction, such as decreased left ventricular developed pressure and dP/dtmax and increased left ventricular end diastolic pressure, was significantly attenuated in female hearts. An excessive NE overflow in the coronary effluent from the postischemic heart in females was much less than that in males. These sex differences were abolished by ovariectomy, but in vivo treatment with 17ß-estradiol recovered it. This ameliorating effect of 17ß-estradiol was not observed in the presence of nitric oxide (NO) synthase inhibitor N-nitro-L-arginine. When NOx (NO2/NO3) levels in the coronary effluent after onset of reperfusion were measured, reversed correlated relationships between NOx production and I/R-induced cardiac dysfunction, and NE overflow, were observed. These findings suggest that sex differences in the postischemic cardiac dysfunction are closely related to the NE overflow from the postischemic heart and that estrogen plays a key role in the cardioprotective effect against I/R injury in female rats, by suppressing NE release via the enhancement of NO production.

Different effects of AT1 receptor antagonist and ET(A) receptor antagonist on ischemia-induced norepinephrine release in rat hearts.

Angiotensin type 1 receptor (AT1R) antagonist and endothelin type A receptor (ET(A)R) antagonist were compared as regards their effects on ischemia-induced exocytotic or carrier-mediated norepinephrine (NE) release from cardiac sympathetic nerve endings. According to the Langendorff technique, isolated rat hearts were subjected to 20-minute or 40-minute global ischemia followed by 30-minute reperfusion. Candesartan (selective AT1R antagonist) and ABT-627 (selective ET(A)R antagonist) were perfused, beginning 15 minutes before ischemia. Candesartan (10 and 100 nM) and ABT-627 (3 µM) suppressed excessive NE overflow (exocytotic release) in the coronary effluent from the heart exposed to 20-minute ischemia. In addition, these agents improved postischemic cardiac dysfunction. On the other hand, the beneficial effects of ABT-627 (1 and 3 µM) on NE overflow (carrier-mediated release) and cardiac dysfunction were also observed in 40-minute ischemia, whereas those were not improved by treatment with candesartan (10 and 100 nM and 1 µM). These findings suggest that both AT1R antagonist and ET(A)R antagonist have ability to inhibit the exocytotic NE release, but the carrier-mediated NE release induced by prolonged ischemia cannot be avoided by AT1R antagonist. Thus, ET(A)R antagonist may be more useful than AT1R antagonist in the clinical settings of ischemic heart disease.

Contribution of nitric oxide in big endothelin-1-induced cardioprotective effects on ischemia/reperfusion injury in rat hearts.

We have recently shown that an appropriate amount of exogenous big endothelin-1 (ET-1) has beneficial effects on ischemia-/reperfusion-induced norepinephrine overflow and cardiac dysfunction in rat hearts and that these effects occur through a conversion to ET-1 by endothelin-converting enzyme and following stimulation of ETB receptor. In this study, we examined the possible involvement of nitric oxide (NO) in the big ET-1-induced cardioprotective effects. According to the Langendorff technique, isolated rat hearts were subjected to 40-minute global ischemia followed by 30-minute reperfusion. Exogenous big ET-1 (0.3 nM) significantly increased NOx (NO2/NO3) level in the coronary effluent after onset of reperfusion. This effect was markedly attenuated by treatment with SM-19712 (selective endothelin-converting enzyme inhibitor), A-192621 (selective ETB receptor antagonist), or NG-nitro-l-arginine (nonselective NO synthase inhibitor), respectively. In addition, N-nitro-l-arginine blunted big ET-1-induced suppression of norepinephrine overflow and improvement of cardiac dysfunction after ischemia/reperfusion. These findings suggest that NO produced by ETB receptor activation plays an important role in exogenous big ET-1-induced actions.

Effects of exogenous big endothelin-1 on postischemic cardiac dysfunction and norepinephrine overflow in rat hearts.

Endothelin-1 (ET-1) is involved in norepinephrine (NE) overflow and cardiac dysfunction after myocardial ischemia/reperfusion via the activation of ET(A) receptors. As ET-1 is generated from big ET-1 via endothelin-converting enzyme (ECE), ischemia/reperfusion-induced cardiac injury may be exacerbated by exogenous big ET-1. The aim of this study was to investigate the influence of exogenously applied big ET-1 on ischemia/reperfusion-induced NE overflow and cardiac dysfunction. According to the Langendorff technique, isolated rat hearts were subjected to 40-min global ischemia followed by 30-min reperfusion. Exogenous big ET-1 (0.1, 0.3 and 1 nM) was perfused, beginning 15 min before ischemia. Unexpectedly, higher doses (0.3 and 1 nM) of big ET-1 significantly improved indices of left ventricular function after ischemia/reperfusion, such as left ventricular developed pressure (LVDP), the maximum value of the first derivative of left ventricular pressure (dP/dt(max)) and left ventricular end diastolic pressure (LVEDP). In addition, big ET-1 significantly suppressed excessive NE overflow in the coronary effluent from the postischemic heart. These effects of big ET-1 were markedly attenuated by treatment with SM-19712 (selective ECE inhibitor) or A-192621 (selective ET(B) receptor antagonist). On the other hand, those were not potentiated even though combined with ABT-627 (selective ET(A) receptor antagonist). From these findings, we suggest that exogenous big ET-1 has beneficial effects on ischemia/reperfusion-induced cardiac injury. It seems likely that big ET-1 is converted to ET-1, locally in the heart, and this ET-1 preferentially binds to ET(B) receptors to exert its related beneficial actions.

Postconditioning improves postischemic cardiac dysfunction independently of norepinephrine overflow after reperfusion in rat hearts: comparison with preconditioning.

We investigated whether the cardioprotective effect of ischemic postconditioning (postC) against ischemia/reperfusion (I/R)-induced cardiac dysfunction is associated with the negative control of I/R-enhanced norepinephrine (NE) overflow, an aggravating factor of I/R injury, in comparison with the effects induced by ischemic preconditioning (preC). According to the Langendorff technique, isolated rat hearts were subjected to 40-minute global ischemia followed by 30-minute reperfusion. PostC, consisting of three cycles of 30-second reperfusion followed by 30-second ischemia at the end of the 40-minute ischemia, improved I/R-induced cardiac dysfunction. However, the potency of this postC-induced improvement was somewhat weaker than that produced by preC, consisting of three cycles of 5-minute ischemia followed by 5-minute reperfusion before 40-minute ischemia. The preC treatment markedly suppressed I/R-enhanced NE overflow, whereas postC had no apparent effect. A nonselective nitric oxide synthase inhibitor, N-nitro-L-arginine, almost completely abolished postC-induced cardiac protection without affecting NE overflow, whereas the effect of preC on I/R-induced cardiac dysfunction and NE overflow was only partially inhibited by N-nitro-L-arginine. These findings indicate that the beneficial effect of postC on I/R-induced cardiac dysfunction depends on nitric oxide and is irrelevant to NE overflow after reperfusion in contrast to the preC effect.

Role of endogenous endothelin-1 in post-ischemic cardiac dysfunction and norepinephrine overflow in rat hearts.

Endothelin-1 and norepinephrine are involved in myocardial ischemia/reperfusion injury. The aim of this study was to investigate the role of endogenously generated endothelin-1 in ischemia/reperfusion-induced norepinephrine overflow and cardiac dysfunction using a nonselective prototype of endothelin-converting enzyme (ECE) inhibitor, phosphoramidon, and a selective ECE inhibitor, SM-19712 (4-chloro-N-[[(4-cyano-3-methyl-1-phenyl-1H-pyrazol-5-yl)amino]carbonyl]benzenesulfonamide, monosodium salt). According to the Langendorff technique, isolated Sprague-Dawley rat hearts were subjected to 40-min global ischemia followed by 30-min reperfusion. Phosphoramidon and SM-19712 were perfused 30 min before ischemia and during reperfusion. Endothelin-1 level in left ventricle was increased by ischemia/reperfusion. This increase in left ventricular endothelin-1 level was suppressed by treatment with SM-19712. SM-19712 significantly improved ischemia/reperfusion-induced cardiac dysfunction such as decreased left ventricular developed pressure and dP/dt(max) and increased left ventricular end diastolic pressure. In addition, this agent suppressed excessive norepinephrine overflow in the coronary effluent from the post-ischemic heart. In contrast, treatment with phosphoramidon further enhanced left ventricular endothelin-1 level and norepinephrine overflow, and significantly worsened cardiac dysfunction after ischemia/reperfusion. These responses such as exaggerated norepinephrine overflow and the cardiac dysfunction observed after ischemia/reperfusion were markedly suppressed in the presence of a selective endothelin ET(A) receptor antagonist, ABT-627 [2R-(4-methoxyphenyl)-4S-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)aminocarbonyl-methyl)-pyrrolidine-3R-carboxylic acid]. These findings indicate that cardiac endothelin-1 production is enhanced by ischemia/reperfusion, and this endogenously increased endothelin-1 is involved in post-ischemic norepinephrine overflow and cardiac dysfunction via the activation of endothelin ET(A) receptors.