Sequential conversion of estradiol-17β to its biologically active catecholestradiols 2-hydroxyestradiol (2-OHE2) and 4-hydroxyestradiol (4-OHE2) contributes importantly to its angiogenic effects on uterine artery endothelial cells derived from pregnant (P-UAECs), but not nonpregnant (NP-UAECs) ewes via estrogen receptor-independent mechanism. Because catecholestradiols and catecholamines exhibit structural similarities and have high affinity for α- and β-adrenergic receptors (ARs), we investigated if the endothelial α- or β-ARs mediate catecholestradiols-induced proliferation of P-UAECs and whether catecholamines alter these responses. Western analyses revealed expression of specific AR subtypes in NP-UAECs and P-UAECs including α2-, β2- and β3-ARs; not α1- and β1-ARs. Levels of β2-ARs and β3-ARs were unaltered by pregnancy; whereas α2-ARs were decreased. Norepinephrine and epinephrine increased P-UAEC, but not NP-UAEC proliferation and these effects were suppressed by propranolol (β-AR blocker) but not phentolamine (α-AR blocker). Catecholamines combinations with 2-OHE2 or 4-OHE2 enhanced P-UAEC mitogenesis. Catecholestradiol-induced P-UAECs proliferation was also inhibited by propranolol but not phentolamine. β2-AR and β3-AR antagonists (ICI 118,551and SR 59230A respectively) abrogated the mitogenic effects of both 2-OHE2 and 4-OHE2. Stimulation of β2-ARs and β3-ARs using Formoterol and BRL37344 dose-dependently stimulated P-UAEC proliferation which was abrogated by ICI 118,551and SR 59230A, respectively. Proliferation effects of both catecholamines and catecholestradiols were only observed in P-UAEC (not NP-UAEC) and were mediated via β2-ARs and β3-ARs. We demonstrate for the first time convergence of the endothelial AR and estrogenic systems in the regulating endothelial proliferation, thus providing a distinct evolutionary advantage for modulating uterine perfusion during stressful pregnancies.

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