Porter M B, Cleaver B D, Peltier M, Robinson G, Thatcher W W, Sharp D C
Department of Animal Science, University of Florida, Gainesville 32611, USA.
J Reprod Fertil. 1997 Jul;110(2):219-29. doi: 10.1530/jrf.0.1100219.
This study compared equine and ovine LH secretory responses to GnRH treatment. Dioestrous mares and ewes were challenged with continuous GnRH for 15 h. Mares that received constant GnRH (110 micrograms h-1) had sustained LH secretion (P < 0.01), whereas LH concentrations in ewes treated with continuous GnRH (25 micrograms h-1) initially increased, then declined and remained low, suggesting GnRH receptor desensitization or downregulation. In addition, progesterone-primed, ovariectomized mares and ewes were challenged with pulsatile or continuous GnRH for 5 days. Plasma LH concentrations were increased by day 5 in mares treated with pulsatile (25 micrograms pulse-1 h-1) and continuous (110 micrograms h-1) GnRH (P < 0.01). Furthermore, mean LH concentrations and time-response curves were not different. In contrast, ewes treated with continuous GnRH (2.5 micrograms h-1) demonstrated LH secretory patterns indicative of GnRH receptor downregulation on day 1 of treatment. LH concentrations in ewes treated with pulsatile GnRH (250 ng pulse-1 h-1) did not differ from controls. In conclusion, pony mares responded continuously to GnRH treatment (pulsatile and continuous), whereas ewes treated with continuous GnRH experienced reduced LH secretion. These findings suggest a unique hypothalamic-pituitary axis in pony mares.
本研究比较了马和羊对促性腺激素释放激素（GnRH）治疗的促黄体生成素（LH）分泌反应。处于间情期的母马和母羊接受连续15小时的GnRH刺激。接受持续GnRH（110微克/小时）的母马有持续的LH分泌（P<0.01），而用连续GnRH（25微克/小时）处理的母羊的LH浓度最初升高，然后下降并保持在低水平，提示GnRH受体脱敏或下调。此外，用孕酮预处理的去卵巢母马和母羊接受脉冲式或连续GnRH刺激5天。接受脉冲式（25微克/脉冲-1小时-1）和连续（110微克/小时）GnRH处理的母马在第5天时血浆LH浓度升高（P<0.01）。此外，平均LH浓度和时间-反应曲线没有差异。相比之下，用连续GnRH（2.5微克/小时）处理的母羊在治疗第1天就表现出LH分泌模式，提示GnRH受体下调。用脉冲式GnRH（250纳克/脉冲-1小时-1）处理的母羊的LH浓度与对照组无差异。总之，矮种母马对GnRH治疗（脉冲式和连续式）有持续反应，而用连续GnRH处理的母羊LH分泌减少。这些发现提示矮种母马存在独特的下丘脑-垂体轴。
