NON-GENOMIC EFFECTS OF ESTROGEN AND THE VESSEL WALL

Estrogen, like other steroids, is now believed to possess rapid membra ne effects independent of the classical gene activation pathway of ste roid action. The presence of membrane estrogen receptors has been demo nstrated in different cell types, but not yet in vascular tissue. In v ivo, estrogen administration rapidly promotes acetylcholine-induced va sodilation of the coronary and peripheral vascular beds of postmenopau sal women. Estrogen also causes relaxation of precontracted isolated a rterial segments and perfused organ preparations, within minutes of ad ministration of the hormone. These rapid vasomotor effects of estrogen may be related to blockade of the cell membrane voltage-dependent cal cium channels, resulting in inhibition of extracellular Ca2+ mobilizat ion and flux. Recently, estradiol has been shown to rapidly affect cyc lic nucleotide turnover in vascular segments, smooth muscle, and epith elial cell cultures, suggesting the possibility of a ''cross-talk'' be tween membrane-mediated events and nuclear receptor activation.