In Vitro Relaxation of Phenylephrine- and Angiotensin II-Contracted Aortic Rings by β-Estradiol

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Abstract
In vivo studies suggest that 17β-estradiol (βE) may regulate vascular tone. Results of recent studies suggest that βE exerts rapid effects on intracellular calcium, possibly via cell surface receptors, distinct from conventional nuclear receptors for steroids. The present study was designed to determine whether βE acutely modifies vascular smooth muscle contractile responses to phenylephrine (PE) and angiotensin II (All). In experiments on tonic responses of aortic rings to 5 × 10−8 mol/L PE, cumulative additions of βE reduced tension at concentrations >10−6 mol/L. Contractile dose responses to PE were determined in rat aortic rings in absence of sex hormones and then after exposure to βE (5 × 10−6 mol/L, n = 6) or vehicle (ETOH, n = 6) for 30 min. βE increased ED50 and reduced maximal responses. Application of 5 × 10−6 mol/L βE for 30 min also reduced the contractile response to 1 mmol/L All from 69 ± 4% (vehicle) to 47 ± 6% (estradiol) of maximal KC1 contraction (P <.025, n = 7). These data suggest that βE acutely attenuates vasoconstrictor responses to PE as well as to All, possibly by an effect exerted at the cell membrane level. Am J Hypertens 1994;7:1065–1069

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