ObjectiveWe have previously shown that conduit arteries of normotensive (WKY) and hypertensive (SHR) Japanese rats differ from normotensive (LN) and hypertensive (LH) Lyon rats in terms of lower aortic thickness and higher collagen III content, whereas differences in vasoactive properties are unknown.MethodsAortic rings with (E+) and without (E−) endothelium were studied under resting and noradrenaline-stimulated conditions in the presence ofNω-nitro-L-arginine (L-NNA) alone or in association with indomethacin, bosentan and/or BQ123.ResultsUnder resting conditions, aortas of normotensive and hypertensive Japanese rats differed from Lyon rats by higher developed tension in the presence of L-NNA and endothelium. In the absence of endothelium, normotensives differed from hypertensives in terms of stronger developed tensions in the presence of L-NNA in the two strains. Addition of indomethacin to L-NNA induced relaxation in E+ SHR and E− WKY and contraction in E− LH. By contrast, tensions were unchanged after addition of bosentan and BQ123. Under stimulated conditions, tensions were equally increased by L-NNA in E+ and unchanged in E− both in Japanese and Lyon rats whether they were normotensive or hypertensive, and indomethacin (but not bosentan) elicited higher response in Lyon than in Japanese rats in E+ and E− aorta.ConclusionUnder NO synthase inhibition, the vasoactive properties of Japanese and Lyon aorta differ in the presence of a cyclo-oxygenase blocker but not endothelin blockers. These results indicate that the aorta vasorelaxant tone is associated to prostanoid regulation in Lyon but not in Japanese rats. This observation appears dependent on the genetic and/or environmental background linked to the origin and not the presence of hypertension.