Objective:To observe the influence of anisodamine on relaxation function of isolated Wistar and spontaneously hypertensive rat(SHR) aortic rings,and to investigate the underlying mechanism.Methods: The SHR aorta rings were irrigated with anisodamine and the effect of anisodamine on relaxation of isolated aortic rings was observed in normal and spontaneous hypertension rats before and after pretreatment with phenylephrine (PE) or L-nitroarginine methylester(L-NAME).Results: The accumulated concentration of anisodamine showed significantly different relaxing effects on PE-precontracted aortic ring with or without endothelium (P<0.05) in normal rats.Anisodamine showed obvious relaxing effect on PE-precontracted aortic ring with and without endothelium,and the relaxing effect was in a dose-dependent manner,with the maximal relaxation being (78.6±6.9)% and (65.76±11.39)%,respectively (P>0.05).Pretreatment with non-selective NOS inhibitor L-NAME significantly inhibited the relaxing effect of anisodamine on the aortic ring with endothelium (P<0.05).L-NAME partially blocked the relaxing effect of anisodamine on SHR rats,with the maximal relaxation being 61% and 11.9% (P<0.01) before and after blocking,respectively.Conclusion: Anisodamine can enlarge isolated aorta of rats through endothelial and smooth muscle.