ALPHA-2-ADRENERGIC RECEPTORS ARE INVOLVED IN THE SUPPRESSION OF LUTEINIZING-HORMONE RELEASE DURING ACUTE FASTING IN THE OVARIECTOMIZED ESTRADIOL-PRIMED RATS

It has been previously reported that the adrenergic system is involved in the control of feeding behavior and LH release. In the present study, the role of the adrenergic receptors in the suppression of LH release during acute fasting are examined by injecting the alpha1-antagonist (prazosin), alpha2-antagonists (idazoxan, SKF 86466-A, piperoxan), or beta-antagonist (propranolol) into the third ventricle of unfasted and 48 h fasted ovariectomized estradiol-treated rats. Blood samples were collected every 6 min for 3 h and the drugs were administered after the first hour of the sampling period. Prazosin caused a significant suppression of LH release in the unfasted animals while idazoxan and propranolol had no significant effects. In contrast, all alpha2-antagonists blocked the inhibitory effect of fasting on LH release and significantly reinstated the suppressed LH release while prazosin and propranolol had no significant effects. We conclude from these results that the suppression of LH release during acute fasting is mediated by alpha2-adrenergic receptors but not alpha1- or beta-adrenergic receptors.