Losartan and enalapril therapies enhance vasodilatation in the mesenteric artery of spontaneously hypertensive rats

Abstract

We studied the effects of 10-week long enalapril and losartan treatments (4 and 15 mg kg −1 day −1, respectively) on mesenteric arterial function in vitro in spontaneously hypertensive rats (SHR) and Wistar–Kyoto rats (WKY). The relaxations of noradrenaline-precontracted rings to acetylcholine, nitroprusside and cromakalim were similar in WKY and enalapril- and losartan-treated SHR, and more pronounced than in untreated SHR. The responses to acetylcholine were attenuated by N G-nitro- l-arginine methyl ester in WKY and drug-treated SHR, but were completely inhibited in untreated SHR. When hyperpolarization of smooth muscle was prevented by KCl-induced precontractions, no differences were found in the relaxations to acetylcholine and nitroprusside between the groups, and the dilatations to cromakalim were abolished. Moreover, in noradrenaline-precontracted rings of drug-treated SHR, the addition of tetraethylammonium attenuated the nitric oxide synthase and cyclooxygenase-resistant relaxations to acetylcholine and abolished the enhanced dilatations to nitroprusside. In conclusion, since the enhancement of vasorelaxation in enalapril- and losartan-treated SHR was abolished by conditions preventing hyperpolarization, the improved vasodilatation following these therapies could be attributed to enhanced vasodilatation via K + channels in this model of hypertension.