Abstract: AIM: To investigate the effects of losartan on the reactivity of the aortic rings in male wistar rats.METHODS: The effects of losartan(3×10^-8-3×10^-5 mol/L) on rat isolated thoracic aortic rings' contraction induced by TXA₂ analog U46619(1 μmol/L) and KCl(60 mmol/L)were observed. In addition, the effect of the NO synthase inhibitor L-NAME(0.1 mmol/L) and the cyclooxygenase inhibitor indomethacin(1μmol/L) on losartan were observed.RESULTS: Losartan (3×10^-8-3×10^-5 mol/L) reduced the constriction induced by U46619(1 μmol/L) in a dose-dependent and endothelium-dependent manner. L-NAME(0.1 mmol/L)significantly shifted the concentration-response curves of losartan to the right. Indomethacin (1 μmol/L) did not change the relaxations of losartan. Losartan did not significantly affect the constriction induced by KCl(60 mmol/L).CONCLUSION: Losartan preferentially antagonizes contraction induced by U46619 in a dose-dependent and endothelium-dependent manner. The vasorelaxation of losartan is relevant to the production of nitrogen and not relevant to the production of prostaglandin.

Key words: Losartan, Angiotasis, Vasodilation, U46619, Nitrogen, Prostaglandin