The inhibitory effect of physiological pattern of testosterone on luteinizing hormone secretion in sheep

Rhim, Tae-jin; Park, Kyoung-sik

Korean Journal of Veterinary Research 1995;35(2):271-278.

Tae-jin Rhim¹, Kyoung-sik Park²

¹College of Life Science & Natural Resources, Sangji University
²Oriental Medicine, Sangji University

면양에서 생리적 분비형태의 테스토스테론이 황체형성호르몬의 분비 억제에 미치는 효과

임태진¹, 박경식²

¹상지대학교 생명자원과학대학
²상지대학교 한의과대학

Abstract

The objective of the present study was to investigate the inhibitory effect of physiologically pulsatile pattern of testosterone(T) on luteinizing hormone(LH) in wethers. To do this, 3 separate experiments were conducted. Infusion rates and patterns needed to produce normal T secretory profiles found in intact rams were established in Experiment 1, the time-course of the suppressive effect of T on circulating LH concentrations was determined in Experiment 2, and the effectiveness of a pulsatile versus a constant pattern of T to suppress LH secretion in wethers was compared in Experiment 3. In Experiment 1, three different doses(25, 50 or $100{mu}g$) of T were injected intravenously to animals to do pharmacokinetic analysis of T. Elimination rate constant, volume of distribution, and total body clearance of T averaged $0.18min^{-1}$, 0.531/kg BW, and 0.091/min/ kg BW, respectively. In Experiment 2, three different doses(192,384, or $768{mu}g/kg/24h$) of T were infused at 4h intervals for 3 days into animals to evaluate the time course of the inhibitory effect of T on mean LH concentration. As duration of T infusion increased, mean LH concentrations gradually reduced. Mean LH concentrations were significantly lower at day 2 or day 3 than at day 0. However, mean LH concentrations did not differ between day 0 and day 1 or between day 2 and day 3. In Experiment 3, animals were subjected to two different intravenous infusion regimens for 3 days: constant T($768{mu}g/kg/24h$) and pulsatile(one pulse every 4h) T($768{mu}g/kg24h$). Blood samples were collected at 10-min intervals for 4h both prior to infusion and during the last 4h of the infusion. Mean LH was more suppressed(p=0.045) by constant T than by pulsatile T. LH pulse amplitude was not affected by constant T or pulsatile T. LH interpulse interval was increased more(p=0.034) by constant T than pulsatile T.

Key Words: testosterone, pharmacokinetics, pulsatile, luteinizing hormone, sheep