SUPPRESSION OF LUTEINIZING-HORMONE RELEASE BY THE ALPHA-1-ADRENERGIC RECEPTOR ANTAGONIST PRAZOSIN IN THE OVARIECTOMIZED FEMALE RHESUS-MONKEY

The effects of adrenergic antagonists on LH release were examined in ovariectomized female rhesus monkeys implanted with indwelling jugular catheters. While the alpha-2-adrenergic antagonist rauwolscine and the vehicle were without effect, the alpha-1-antagonist prazosin suppressed LH release. In 5 of the 8 monkeys tested, LH pulses were completely arrested; in the remaining 3 monkeys, small LH pulses were detectable after the administration of 0.2 mg/kg prazosin. In a second series of experiments, the effects of three different doses of prazosin were examined. Doses of 0.1 mg/kg and 0.4 mg/kg suppressed LH release in a manner indistinguishable from that of the 0.2 mg/kg dose. Finally, the ability of the pituitary to respond to a bolus of LHRH during the prazosin-induced suppression was tested. In all 6 animals, the injection of LHRH during the time when LH was suppressed by prazosin resulted in a marked increase in LH release. These results indicate 1) that alpha-1-adrenergic receptors but not alpha-2 receptors are important for pulsatile LH secretion, 2) that varying the dose of prazosin administered does not alter the effect of the drug on LH release within the range of doses tested, and 3) the pituitary is able to respond to LHRH with an increase in LH release during the prazosin-induced suppression period.