Effects of the Catechol and Methoxy Metabolites of 17β-Estradiol on Nitric Oxide Production by Ovine Uterine Artery Endothelial Cells

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 beta, 2-hydroxyestradiol (2-OHE2), 4-hydroxyestradiol (4-OHE2), 2-methoxyestradiol (2-ME2), and 4-methoxyestradiol (4-ME2) play a role in mediating vasodilation and rises in UBF during pregnancy. We previously showed that the E-2 beta metabolites stimulate prostacyclin production in pregnancy-derived ovine uterine artery endothelial cells (P-UAECs); however, it is unknown whether the E-2 beta metabolites also induce NO production. Herein, UAECs derived from nonpregnant and pregnant ewes were used to test the hypothesis that E-2 beta 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 beta metabolite-induced NO production. E-2 beta and its metabolites increased total nitric oxide metabolites (NOx) levels (NO2 + NO3) in P-UAECs, but not in NP-UAECs. Pretreatment with combined 1 mu mol/L 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride (MPP; ER-alpha antagonist) and 1 mu mol/L 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP; ER-beta antagonist) inhibited the rises in NOx levels stimulated by E-2 beta and 2-ME2, but had no effect on 2-OHE2-, 4-OHE2-, or 4-ME2-stimulated rises in NOx levels. Pretreatment with yohimbine (alpha(2)-AR antagonist) and propranolol (beta(2,3)-AR antagonist) inhibited the rises in NOx levels stimulated by 2-OHE2, but not by E-2 beta, 4-OHE2, 2-ME2, or 4-ME2. These data demonstrate that E-2 beta 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.