Role of alpha-receptors in estrogen-induced vasodilation in nonpregnant sheep.
Estradiol-17 beta (E2) produces vasodilation in several systemic vascular beds, but most extensively in the nonpregnant uterus. It has been postulated that E2 induces this vasodilation via blockade of vascular alpha-adrenergic receptors. This hypothesis was tested in six chronically instrumented, nonpregnant sheep by comparing the systemic and uterine hemodynamic responses to intravenous E2, to an alpha-adrenergic receptor blocker, phentolamine, and to both agents given together. Uterine blood flow (UBF) increased significantly after E2 administration, from 20 +/- 7 to 233 +/- 37 (SE) ml/min. In contrast, phentolamine had no detectable effect on UBF or on the UBF response to E2 when both were given together. Similar contrasting responses were observed in the effects of E2 and/or phentolamine on the systemic vasculature. When responses to alpha-agonists were evaluated, there was no evidence of alpha-blockade following E2 despite the substantial vasodilation; in contrast, alpha-blockade was present during phentolamine administration when no vasodilation was noted. Therefore, we conclude that E2-induced vasodilation in chronically instrumented sheep is not mediated through blockade of vascular alpha-adrenergic receptors.
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D000818:Animals; D001794:Blood Pressure; D002302:Cardiac Output; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D010646:Phentolamine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D012039:Regional Blood Flow; D012756:Sheep / Q000502:physiology*; D014599:Uterus / Q000098:blood supply*; D014655:Vascular Resistance / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects*
D011942:Receptors, Adrenergic, alpha; D004958:Estradiol; D010646:Phentolamine