Abstract
Metabolism of estradiol-17β to 2-hydroxyestradiol, 4-hydroxyestradiol, 2-methoxyestradiol, and 4-methoxyestradiol contributes importantly to the vascular effects of estradiol-17β in several vascular beds. However, little is known about the role of estradiol-17β metabolites via the different estrogen receptors (ER-α/ER-β) on de novo endothelial prostacyclin and thromboxane production. We hypothesized that estradiol-17β and its metabolites, via ER-α or ER-β, can enhance the prostacyclin/thromboxane ratio through the classic phospholipase A(2), cyclooxygenase-1, and prostacyclin synthase pathway in ovine uterine artery endothelial cells (UAECs) derived from pregnant (P-UAECs) versus nonpregnant (NP-UAECs) ewes. Western analyses showed higher expression of phospholipase A(2), cyclooxygenase-1, and prostacyclin synthase in UAECs from the pregnant state, whereas thromboxane synthase was lowered in UAECs from the pregnant state. In UAECs from the pregnant state, estradiol-17β, 2-hydroxyestradiol, 4-hydroxyestradiol, 2-methoxyestradiol and 4-methoxyestradiol concentration and time-dependently increased prostacyclin compared with controls. Prostacyclin increases in UAECs from the nonpregnant state were of a lower magnitude. Estradiol-17β and its metabolites stimulated higher prostacyclin/thromboxane ratios in UAECs from the pregnant state compared with UAECs from the nonpregnant state. Estradiol-17β-induced prostacyclin increases were abrogated by the antagonists SC-560 (cyclooxygenase-1), U-51605 (Prostacyclin synthase), ICI 182780 (ICI; both ER-α/β), and 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinyleth oxy)phenol]-1H-pyrazole dihydrochloride (MPP; ER-α), but not by 4-[2-phenyl-5,7-bis (trifluoromethyl) pyrazolo[1,5-a]pyrim idin-3-yl]phenol (PHTPP; ER-β). Prostacyclin increases induced by its metabolites were abolished by SC-560 and U-51605, but unaltered by ICI, MPP, or PHTPP. Our findings demonstrate that estrogen via primarily ER-α and its metabolites via ER-independent mechanisms influence the de novo endothelial biosynthesis of prostacyclin, which may be important in the regulation of vascular tone. These findings also shed light on the complexities of estrogen signaling via its metabolism and the functional heterogeneity of the ERs.