Daily Luteinizing Hormone Release in Ovariectomized Hamsters: Effect of Barbiturate Blockade1

Abstract

In the absence of the ovary, female hamsters exhibit a daily surge of LH between 1500 and 1900 h (lights on 0600–2000 h). Phenobarbital (100 mg/kg, s.c.) injected at 1400 h completely suppressed the LH surge in females that had been castrated 15 days previously. Phenobarbital was also effective in long-term (15 week) castrate animals. In both cases, surge release of LH was delayed 24 h, occurring at the expected time, the day after injection. In a final experiment, phenobarbital was injected at various times in the afternoon in females castrated for 3 weeks. Phenobarbital effectively prevented LH release when administered at any time from 1100 to 1500 h. Injections at 1600 h partially suppressed the LH peak, which occurred at about the same time.