IN-VITRO RELAXATION OF PHENYLEPHRINE-CONTRACTED AND ANGIOTENSIN-II-CONTRACTED AORTIC RINGS BY BETA-ESTRADIOL

In vivo studies suggest that 17 beta-estradiol (beta E) may regulate v ascular tone. Results of recent studies suggest that beta E exerts rap id effects on intracellular calcium, possibly via cell surface recepto rs, distinct from conventional nuclear receptors for steroids. The pre sent study was designed to determine whether beta E acutely modifies v ascular smooth muscle contractile responses to phenylephrine (PE) and angiotensin II (AII). In experiments on tonic responses of aortic ring s to 5 x 10(-8) mol/L PE, cumulative additions of beta E reduced tensi on at concentrations >10(-6) mol/L. Contractile dose responses to PE w ere determined in rat aortic rings in absence of sex hormones and then after exposure to beta E (5 x 10(-6) mol/L, n = 6) or vehicle (ETOH, n = 6) for 30 min. beta E increased ED(50) and reduced maximal respons es. Application of 5 x 10(-6) mol/L beta E for 30 min also reduced the contractile response to 1 mmol/L AII from 69 +/- 4% (vehicle) to 47 /- 6% (estradiol) of maximal KCl contraction (P <.025, n = 7). These d ata suggest that beta E acutely attenuates vasoconstrictor responses t o PE as well as to AII, possibly by an effect exerted at the cell memb rane level.