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 Eβ, 2-hydroxyestradiol (2-OHE), 4-hydroxyestradiol (4-OHE), 2-methoxyestradiol (2-ME), and 4-methoxyestradiol (4-ME) play a role in mediating vasodilation and rises in UBF during pregnancy. We previously showed that the Eβ metabolites stimulate prostacyclin production in pregnancy-derived ovine uterine artery endothelial cells (P-UAECs); however, it is unknown whether the Eβ metabolites also induce NO production. Herein, UAECs derived from nonpregnant and pregnant ewes were used to test the hypothesis that Eβ 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 Eβ metabolite-induced NO production. Eβ and its metabolites increased total nitric oxide metabolites (NOx) levels (NO + NO) 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 Eβ and 2-ME, but had no effect on 2-OHE-, 4-OHE-, or 4-ME-stimulated rises in NOx levels. Pretreatment with yohimbine (α-AR antagonist) and propranolol (β-AR antagonist) inhibited the rises in NOx levels stimulated by 2-OHE, but not by Eβ, 4-OHE, 2-ME, or 4-ME. These data demonstrate that Eβ 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.