Abstract 244: Increased Expression and Enhanced Vasorelaxation Activity of Specific Estrogen Receptor Subtypes in the Aorta and Mesenteric Vessels during Pregnancy

Abstract

Pregnancy (Preg) is associated with hormonal and vascular changes, and estrogen (E2) may promote systemic vasodilation during Preg; however, the specific E2 receptor (ER), post-ER signaling mechanisms and vascular bed involved are unclear. To test if Preg is associated with distinct expression/activity of ERs in different blood vessels, BP and plasma E2 were measured in virgin and day-19 Preg rats, and the aorta, carotid, mesenteric and renal artery were isolated for measurement of ERα, ERβ and GPR30 expression, and the responses to E2 and specific ER agonists PPT (ERα), DPN (ERβ) and G1 (GPR30). BP was in Preg (89±6) < virgin (98±4mmHg), and plasma E2 was in Preg (120.5±5.8) > virgin (94.3±7.5pg/ml). Western blots revealed increased ERα and ERβ in aorta and mesenteric artery and GPR30 in aorta of Preg vs virgin. Immunohistochemistry revealed that the increases in ERs were mainly in intima and media. E2 and PPT caused greater relaxation of aorta of Preg (52.8±5.5, 49.3±11.4) than virgin (30.0±3.9, 19.3±3.8%) and of mesenteric artery of Preg (77.9±4.7, 75.4±4.5) than virgin (57.4±5.9, 46.5±9.5%), but similar relaxation in carotid and renal artery of Preg vs virgin. DPN and G1 caused greater relaxation in mesenteric and renal artery (15 to 30%) than aorta and carotid artery (<10%), but only aortic relaxation to G1 was in Preg (26.2±4.4) > virgin (5.3±6.7%). The NOS inhibitor L-NAME ± EDHF blocker tetraethylammonium or endothelium removal reduced PPT relaxation in aorta, suggesting an endothelium-dependent mechanism, but did not affect E2, PPT, DPN or G1-induced relaxation in other vessels, suggesting endothelium-independent mechanisms. PPT caused relaxation of Ca 2+ entry-dependent KCl contraction of mesenteric artery that was in Preg (69.7±5.5) > virgin rats (52.9±8.11%). Thus, during pregnancy, an increased ERα expression in endothelial and smooth muscle layers of aorta and mesenteric artery is associated with increased ERα-mediated relaxation via endothelium-derived vasodilators and direct inhibition of Ca 2+ entry pathways, supporting a role of aortic and mesenteric arterial ERα in pregnancy-associated systemic vasodilation. GPR30 may contribute to aortic dilation while the enhanced ERβ may mediate other genomic vascular effects during pregnancy.