DIRECT RELAXING EFFECT OF ESTRADIOL-17-BETA AND PROGESTERONE ON RAT SAPHENOUS ARTERY

Although estrogen has been reported to relax large coronary arteries i mmediately, its direct acute effect on small vessel tone has not been fully defined. In this study, we investigated the effect of estradiol- 17 beta and progesterone on isolated rat saphenous artery segments-wit h an internal radius of 250 mu m-by measuring the outer diameter of th e vessels using in vitro angiometry. Estradiol and progesterone at con centrations of 1-100 and 8.6-86 mu M induced a rapid, dose-dependent r elaxation of the arterial segments precontracted with norepinephrine. Maximal changes of diameters were 85.8 +/- 10 and 90.9 +/- 8%. Clomiph ene citrate, a cytoplasmic receptor antagonist, did not diminish this action of estradiol, with the exception of the highest concentrations of the hormone. Thus a nongenomic pathway for this effect can be suspe cted. Dexamethasone did not induce similar vasodilation. It is conclud ed that estradiol and progesterone have similar rapid vasorelaxing eff ects on small muscular arteries as found previously on coronary arteri es. (C) 1998 Academic Press.