Treatment of oophorectomized guinea pigs with intrauterine 17 beta-estradiol pellets may modulate myometrial beta-adrenergic receptor binding properties
Hatjis, C.G.; Grogan, D.M.; Koritnik, D.R.
American Journal of Obstetrics and Gynecology 161(6 Pt 1): 1628-1632
1989
ISSN/ISBN: 0002-9378 PMID: 2574950 Document Number: 338185
Intrauterine 17 beta-estradiol pellets can induce an up-regulation of guinea pig myometrial beta-adrenergic receptor density and l-isoproterenol-dependent adenylate cyclase activity. Does 17 beta-estradiol influence the ability of beta-adrenergic receptors to form a "high affinity" state with l-isoproterenol, which is a necessary step for adenylate cyclase activation? Nonpregnant, oophorectomized guinea pigs received intrauterine pellets of either placebo, 17 beta-estradiol, progesterone, or 17 beta-estradiol plus progesterone for 1 week. 17 beta-Estradiol resulted in pharmacologic, whereas progesterone resulted in physiologic plasma 17 beta-estradiol and progesterone concentrations, respectively. The affinity of myometrial beta-adrenergic receptors for l-isoproterenol was measured by percentage of inhibition of -[125I]cyanopindolol binding. In all groups, the competition curves in the presence of magnesium chloride could be resolved into two affinity states of the beta-adrenergic receptor, "high" and "low," respectively. The ratio of their dissociation constants was not influenced by hormonal treatment. However, the relative concentration of beta-adrenergic receptors in the high affinity state was significantly higher in the 17 beta-estradiol-treated group than that in the control group. This correlates with the up-regulation in myometrial adenylate cyclase activity and suggests that myometrial beta-adrenergic receptor-adenylate cyclase function may be modulated by 17 beta-estradiol.