Regulation of uterine estrogen receptors (ER) by beta-adrenergic stimulation in immature rats.

The effects of a 3-day intramuscular (i.m.) administration of clenbuterol (25 micrograms/Kg), propranolol (12 mg/kg), clenbuterol (25 micrograms/kg) plus propranolol (12 mg/Kg) and estradiol (0.5 microgram) upon the female reproductive system were investigated in immature Sprague-Dawley rats. Clenbuterol and estradiol treatments induced a significant increase in uterus weight and in relative uterus weight, whereas in the groups treated with propranolol and clenbuterol plus propranolol no differences were detected versus controls. The uterine estrogen receptor levels were significantly increased by clenbuterol administration. In the rats dosed with propranolol and clenbuterol plus propranolol, no modifications occurred in estrogen receptor concentrations when compared with control values. Uterine progesterone receptors were never significantly affected by any of the considered treatments. Data obtained indicate that clenbuterol treatment induces an increase in uterus weight and in estrogen receptor levels and that these effects are regulated by acute beta-adrenergic stimulation, as the contemporaneous administration of high doses of a beta-blocker inhibit such effects.