Effects of estrogen on nitric oxide biosynthesis and vasorelaxant activity in sheep uterine and renal arteries in vitro, ,

OBJECTIVES: Our purpose was to determine whether estrogen alters the relaxation responses to bradykinin and superoxide dismutase of the uterine and renal arteries and to determine the role of nitric oxide in that response. STUDY DESIGN: Ten nulliparous, ovariectomized nonpregnant sheep received either estradiol-17β or vehicle solution. In vitro studies evaluating vasorelaxation were done with either bradykinin or superoxide dismutase. The nitric oxide inhibitor Nω-nitro-L-arginine methyl ester was used to determine the role of nitric oxide in this process. Nitric oxide synthase activity was assessed by measuring citrulline generation. RESULTS: We found a dose dependency of relaxation to bradykinin and superoxide dismutase. Estrogen enhanced this response in uterine arteries. Estrogen increased citrulline generation in uterine but not renal arteries. Nω-nitro-L-arginine methyl ester blocked relaxation responses and citrulline generation in both arteries. CONCLUSION: In nonpregnant sheep we found that nitric oxide release and nitric oxide synthase activity is enhanced by estrogen in the uterine arteries but not in the renal arteries. Increases in nitric oxide synthase activity may be important in the hyperemic response of the uterus during estrus. (AM J OBSTET GYNECOL 1996;174:1043-9.)