Effects of adrenergic antagonists on LH surge in short-term ovariectomized-steroids-primed rats.

Characterization of adrenergic stimuli on luteinizing hormone (LH) release induced by ovarian steroids in short-term ovariectomized (OVX) rats was studied. Female Sprague-Dawley rats were OVX about 1000 h on the diestrous day 1. After ovariectomy, rats were immediately inserted estradiol-containing Silastic capsules s.c. and implanted atrial Silastic tubing for frequent blood samplings. All the rats received 2 mg of progesterone s.c. at 0930 h the next morning. At 1200 h, the rats received additional treatments: a saline vehicle, prazosin HC1 (an alpha 1-adrenergic antagonist), yohimbine HC1 (an alpha 2-adrenergic antagonist), or propranolol HC1 (a beta-adrenergic antagonist) s.c., respectively. Two different doses of individual adrenergic antagonists were used on an equimolar basis in order to show their effectiveness on steroids-induced LH secretion. Blood samples were collected before and 1, 3, and 5 hours after the treatments through indwelt tubings. LH surge induced by ovarian steroids was suppressed/delayed by prazosin and yohimbine, but potentiated by propranolol in a dose-dependent manner. Results suggested that the hypothalamic alpha 1-, alpha 2-, and beta-adrenoreceptors were involved in the control of LH surge in the short-term OVX-steroids-primed rats. Principally, the alpha 1- and alpha 2-adrenoreceptors played a facilitatory role, and the beta-adrenoreceptors played an inhibitory role in the regulation of LH surge induced by ovarian steroids.