Abstract
Nitric oxide (NO) production is essential to facilitate rises in uterine blood flow (UBF) during pregnancy. It has been proposed that the metabolites of E(2)β, 2-hydroxyestradiol (2-OHE(2)), 4-hydroxyestradiol (4-OHE(2)), 2-methoxyestradiol (2-ME(2)), and 4-methoxyestradiol (4-ME(2)) play a role in mediating vasodilation and rises in UBF during pregnancy. We previously showed that the E(2)β metabolites stimulate prostacyclin production in pregnancy-derived ovine uterine artery endothelial cells (P-UAECs); however, it is unknown whether the E(2)β metabolites also induce NO production. Herein, UAECs derived from nonpregnant and pregnant ewes were used to test the hypothesis that E(2)β metabolites stimulate NO production in a pregnancy-specific manner. Specific estrogen receptor (ER) and adrenergic receptor (AR) antagonists were used to determine the roles of ERs or ARs in E(2)β metabolite-induced NO production. E(2)β and its metabolites increased total nitric oxide metabolites (NOx) levels (NO(2) + NO(3)) in P-UAECs, but not in NP-UAECs. Pretreatment with combined 1 µmol/L 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride (MPP; ER-α antagonist) and 1 µmol/L 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP; ER-β antagonist) inhibited the rises in NOx levels stimulated by E(2)β and 2-ME(2), but had no effect on 2-OHE(2)-, 4-OHE(2)-, or 4-ME(2)-stimulated rises in NOx levels. Pretreatment with yohimbine (α(2)-AR antagonist) and propranolol (β(2,3)-AR antagonist) inhibited the rises in NOx levels stimulated by 2-OHE(2), but not by E(2)β, 4-OHE(2), 2-ME(2), or 4-ME(2). These data demonstrate that E(2)β metabolites stimulate NO synthesis via ERs or ARs in UAECs in a pregnancy-specific manner, suggesting that these metabolites contribute to rises in vasodilation and UBF during pregnancy.