Estradiol relaxes rat aorta via endothelium-dependent and -independent mechanisms

The effects of estrogen on arterial function are heterogeneous with respect to vessel and/or species. We have investigated 17beta-estradiol-induced relaxation in isolated rat aorta with regard to the role of the vascular endothelium and ionic mechanisms. Estrogen induced a concentration-dependent relaxation of 46.5 +/- 7.9% and 70.1 +/- 12.2% (10(-8) and 10(-7)M), which was reduced by endothelial denudation. Furthermore, L-nitroarginine methyl ester completely abrogated this effect; however, estradiol did not relax KCl-contracted rings. Tetraethyl ammonium (1 mmol/l) completely blocked estradiol-induced relaxation. Estradiol increased [cGMP] in isolated aortic rings via NO, but did not significantly affect NOS activity in endothelial cells. Thus, estrogen can relax rat aorta in vitro via both endothelium-dependent and -independent mechanisms involving the NO/cGMP and potassium channel signaling system.