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

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, ni troprusside and cromakalim were similar in WKY and enalapril- and losartan- treated SHR, and more pronounced than in untreated SHR. The responses to ac etylcholine were attenuated by N-G-nitro-L-arginine methyl ester in WKY and drug-treated SHR, but were completely inhibited in untreated SHR. When hyp erpolarization of smooth muscle was prevented by KCl-induced precontraction s, no differences were found in the relaxations to acetylcholine and nitrop russide between the groups, and the dilatations to cromakalim were abolishe d. Moreover, in noradrenaline-precontracted rings of drug-treated SHR, the addition of tetraethylammonium attenuated the nitric oxide synthase and cyc looxygenase-resistant relaxations to acetylcholine and abolished the enhanc ed dilatations to nitroprusside. In conclusion, since the enhancement of va sorelaxation in enalapril- and losartan-treated SHR was abolished by condit ions preventing hyperpolarization, the improved vasodilatation following th ese therapies could be attributed to enhanced vasodilatation via K+ channel s in this model of hypertension. (C) 1999 Elsevier Science B.V. All rights reserved.