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 E2β, 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 E2β metabolites stimulate prostacyclin production in pregnancy-derived ovine uterine artery endothelial cells (P-UAECs); however, it is unknown whether the E2β metabolites also induce NO production. Herein, UAECs derived from nonpregnant and pregnant ewes were used to test the hypothesis that E2β 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 E2β metabolite-induced NO production. E2β and its metabolites increased total nitric oxide metabolites (NOx) levels (NO2 + NO3) 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 E2β and 2-ME2, but had no effect on 2-OHE2-, 4-OHE2-, or 4-ME2-stimulated rises in NOx levels. Pretreatment with yohimbine (α2-AR antagonist) and propranolol (β2,3-AR antagonist) inhibited the rises in NOx levels stimulated by 2-OHE2, but not by E2β, 4-OHE2, 2-ME2, or 4-ME2. These data demonstrate that E2β 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.