Ayman Geddawy

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 ETA 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/dtmax) 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 ETB receptor antagonist). On the other hand, those were not potentiated even though combined with ABT-627 (selective ETA 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 ETB receptors to exert its related beneficial actions.

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, NG-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.

Influence of Hypoxia on Endothelium-Derived NO-Mediated Relaxation in Rat Carotid, Mesenteric and Iliac Arteries

Individual vascular beds exhibit differences in vascular reactivity. The present study examined the influence of hypoxia on endothelium-dependent, especially nitric oxide (NO)-mediated, relaxation in the isolated rat common carotid, superior mesenteric and external iliac arteries. Hypoxia for 1 and 3 h had no effects on the relaxations caused by acetylcholine (ACh) and sodium nitroprusside (SNP) in common carotid and external iliac arteries. In addition, NO synthase inhibitor NG-nitro-L-arginine (L-NA, 10 μmol/l)-resistant, endothelium-dependent relaxations by ACh were also unaffected by hypoxia in these arteries. On the other hand, ACh-induced relaxation in superior mesenteric arteries was significantly impaired by exposure to hypoxia, while this condition did not affect the relaxation induced by SNP or ACh in the presence of L-NA. This impairment was partially prevented by treatment with tempol (3 mmol/l), a superoxide scavenger. These findings demonstrate a marked heterogeneity in response to hypoxia in rat arteries. Briefly, acute hypoxia induces impairment of endothelium-derived NO-mediated relaxation through the decrease in its bioavailability in the superior mesenteric, but not in common carotid or external iliac, arteries. Furthermore, superoxide seems to be one causal factor responsible for the undesirable effect of hypoxia.

Effects of Liraglutide and Vitamin E in Fructose-Induced Metabolic Syndrome in Rats

Background: Metabolic syndrome (MetS) is a growing worldwide health problem. However, there is yet no effective therapy for MetS. The present work investigated the effect of liraglutide, a synthetic glucagon-like peptide-1 and vitamin E on fructose-induced MetS in rats. Summary: Liraglutide (0.3 mg/kg/day) and vitamin E (100 mg/kg/day) were administered either alone or in combination with high fructose-fed male rats for 6 weeks. Fructose-fed rats developed metabolic disorders assessed by visceral fat index, serum glucose, serum insulin, homeostasis model assessment-insulin resistance and serum lipids profile and hepatic disorders assessed by liver index, serum alanine aminotransferase and aspartate aminotransferase and steatohepatitis in histopathology. This study showed that liraglutide, vitamin E and their combination significantly ameliorated the fructose-induced metabolic and hepatic disorders. Key Messages: These results indicate a potential therapeutic benefit of liraglutide and vitamin E combination in prevention of MetS. Their protective effects might rely on their antioxidant effects as well as on the inhibition of tumor necrosis factor-α.

Corrigendum to "Chronic administration of nicotine-free cigarette smoke extract impaired endothelium-dependent vascular relaxation in rats via increased vascular oxidative stress" [J Pharmacol Sci 118 (2012) 206-214].

Cigarette smoking has been implicated in the initiation and progression of cardiovascular disorders and atherosclerosis. Here, we examined the effects of nicotine-free cigarette smoke extract (CSE) on the regulation of cardiovascular function. Rats were subcutaneously administered PBS or nicotine-free CSE at 0.05 to 1.5 mL/day per rat for 4 weeks. Blood pressure, cardiac function, and vascular responsiveness were measured at 4 weeks after administration. Furthermore, acute effects of nicotine-free CSE were also studied in the aorta isolated from normal rats. Blood pressure and left ventricular systolic pressure (LVSP) were significantly increased in the nicotinefree CSE–administered rats, but heart rate, dP/dtmax, and dP/dtmin were not affected. Endotheliumdependent relaxation by acetylcholine (ACh) in the nicotine-free CSE–treated rats was significantly attenuated compared to PBS-treated rats, but endothelium-independent relaxation by sodium nitroprusside (SNP) did not differ. Pretreatment with superoxide dismutase restored the attenuated ACh-induced relaxation. Contractions by phenylephrine, angiotensin II, and KCl did not differ between two groups. In vitro acute nicotine-free CSE treatment did not alter the response to ACh or SNP. These results suggest that chronic nicotine-free CSE administration impairs endothelial function by increased production of superoxide derived from the vascular wall components other than smooth muscles and induces slight hypertension accompanied with LVSP elevation.