THE INFLUENCE OF GONADOTROPIN-RELEASING HORMONE ON PUBERTAL DEVELOPMENT OF DAIRY BULLS (REPRODUCTION, PREPUBERTAL, LH, TESTOSTERONE)

摘要

The purpose of this investigation was to determine if the administration of GnRH to immature Holstein bulls would increase the secretion of luteinizing hormone (LH), necessary for pubertal development. Preliminary experiments investigated the sensitivity of GnRH potency to storage up to one month at 37(DEGREES)C. GnRH injected into immature rats (0.25, 0.5, and 1.0 (mu)g per 100 g body weight) elevated serum LH concentrations consistently, regardless of GnRH age, indicating no loss in GnRH potency.;Immature Holstein bulls received either a continuous, injected, or pulsatile dose(s) of GnRH. The continuous administration of (0.3 or 0.6 (mu)g/hr) GnRH may have stimulated initiation of spermatogenesis but the results were inconclusive. Intravenous injection of (2, 4, 8, 10, or 32 (mu)g) GnRH produced elevated serum LH concentrations in response to all doses. The serum LH concentrations produced by the 2 and 4 (mu)g doses were similar to reported pubertal serum concentrations of 4-15 ng/ml. Serum testosterone increased from 0.42 to 0.55 ng/ml but were not significantly different from control values.;Pulsatile administration of (2, 4, and 8 (mu)g) GnRH to an infant bull by computerized infusion pump increased serum LH concentrations. Initially, 8 (mu)g doses of GnRH were more effective in increasing serum LH concentrations. As the animal aged 2 and 4 (mu)g doses of GnRH also produced increases in serum LH concentrations. The 2 and 4 (mu)g doses of GnRH, repeatedly administered every 2 or 4 hr, increased serum LH concentrations with each pulse. When these doses were followed by a 4 or 8 (mu)g dose respectively, there were significant increases in serum LH concentrations. With a 8 (mu)g dose repeatedly administered every 2 hr, no significant increase in serum LH concentration occurred.;GnRH is a stable hormone when incubated at body temperature for one month. The 2 and 4 (mu)g doses of GnRH, injected every 2 to 4 hr, produce increases in serum LH necessary for pubertal development in Holstein bulls.