title: Alpha adrenergic responses of blood vessels of rabbits after ovariectomy and administration of 17 beta-estradiol.
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 17 beta-estradiol (100 micrograms 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 degrees 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.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001808:Blood Vessels / Q000502:physiology*; D000068438:Brimonidine Tartrate; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010052:Ovariectomy; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D014661:Vasoconstriction / Q000187:drug effects; D014666:Vasomotor System / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D004958:Estradiol; D009638:Norepinephrine; D011224:Prazosin