Acute inhibitory effects of antiserum to gonadotropin-releasing hormone in ovariectomized rats. Evidence for pulsatile secretion of gonadotropin-releasing hormone.

To evaluate the dependence of pulsatile secretion of luteinizing hormone (LH) on gonadotropin-releasing hormone (GnRH), the acute effects of immunoneutralization of endogenous GnRH on plasma LH were compared in ovariectomized rats with phenobarbital treatment and hypophysectomy. Anti-GnRH produced a rapid dose-dependent decrease in plasma LH and LH pulse amplitude. Pulsatile secretion of LH was eliminated in 6 of 12 rats treated with the highest dose of anti-GnRH, but plasma LH was still 50% of control values 3 h after treatment. Frequency of LH pulses was unchanged in animals which had persistence of pulsatile secretion of LH. Phenobarbital eliminated pulsatile secretion of LH transiently. Hypophysectomized rats displayed a striking decrease in plasma LH which could be resolved into two exponential components with half-lives of 16 and 70 min. The initial half-life of plasma LH from untreated rats determined after LH pulses was also 16 min. These studies support the hypothesis that pulses of GnRH induce the pulsatile pattern of plasma LH and may be responsible for all LH secretion in ovariectomized rats.