Alpha adrenergic responses of blood vessels of rabbits after ovariectomy and administration of 17β-estradiol

V. Gisclard, N. A. Flavahan, P. M. Vanhoutte

Research output: Contribution to journalArticlepeer-review

Abstract

Experiments were designed to determine the effect of estrogen pretreatment on alpha adrenergic responsiveness of blood vessels of the rabbit. Rabbits were ovariectomized and, after 8 days of recovery, treated with 17β-estradiol (100 μg i.m.; estrogen group) or solvent (control group) for 4 days. Rings of saphenous vein and femoral artery (both without endothelium) were mounted for isometric tension recording in organ chambers filled with modified Krebs-Ringer bicarbonate solution (37°C), gassed with 95% O2-5% CO2. All experiments were performed in the presence of inhibitors of neuronal uptake, extraneuronal uptake and beta adrenoceptors. In the saphenous vein, the estrogen treatment did not significantly affect the concentration-effect curves evoked by norepinephrine (either under control conditions or after alpha-1 or alpha-2 adrenergic blockade), phenylephrine (an alpha-1 adrenergic agonist) or UK 14,304 (an alpha-2 adrenergic agonist). In the femoral artery, estrogen treatment depressed the contractile responses evoked by norepinephrine (under control conditions) but not those produced by phenylephrine; UK 14,304 did not evoke a contractile response. The depressant effect of estrogen treatment on the concentration-effect curve to norepinephrine in the femoral artery was prevented by the alpha-2 adrenergic antagonist, rauwolscine. The results in the femoral artery but not in the saphenous vein suggest that estrogens depress alpha-2 but not alpha-1 adrenergic responsiveness. In the femoral artery, alpha-2 adrenoceptor stimulation does not cause contraction per se but apparently can facilitate alpha-1 adrenergic responses. This probably results from a reduced density of alpha-2 adrenoceptors in this blood vessel. Thus, the inhibitory influence of estrogen on alpha adrenergic responses of vascular smooth muscle may depend on the density of adrenoceptors (or spare receptors).

Original languageEnglish (US)
Pages (from-to)466-470
Number of pages5
JournalJournal of Pharmacology and Experimental Therapeutics
Volume240
Issue number2
StatePublished - 1987
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

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