Stackpole C A, Turner A I, Clarke I J, Lambert G W, Tilbrook A J
Department of Physiology, Monash University, Clayton, Victoria 3800, Australia.
Biol Reprod. 2003 Oct;69(4):1158-64. doi: 10.1095/biolreprod.103.016428. Epub 2003 May 28.
Stress responses are thought to act within the hypothalamopituitary unit to impair the reproductive system, and the sites of action may differ between sexes. The effect of isolation and restraint stress on pituitary responsiveness to GnRH in sheep was investigated, with emphasis on possible sex differences. Experiments were conducted during the breeding season and the nonbreeding season. In both experiments, 125 ng of GnRH was injected i.v. every 2 h into hypothalamopituitary disconnected, gonadectomized rams and ewes on 3 experimental days, with each day divided into two periods. During the second period on Day 2, isolation and restraint stress was imposed for 5.5 h. Plasma concentrations of LH and cortisol were measured in samples of blood collected from the jugular vein. In the second experiment (nonbreeding season), plasma concentrations of epinephrine, norepinephrine, 3,4-dihydroxyphenylalanine, and 3,4-dihydroxyphenylglycol were also measured. In both experiments, there was no effect of isolation and restraint stress on plasma concentrations of cortisol in either sex. During the breeding season, there was no effect of isolation and restraint stress on plasma concentrations of LH in either sex. During the nonbreeding season, the amplitude of the first LH pulse after the commencement of stress was significantly reduced (P < 0.05) in rams and ewes. In the second experiment, during stress there was a significant increase (P < 0.05) in plasma concentrations of epinephrine in rams and ewes and significantly higher (P < 0.05) basal concentrations of norepinephrine in ewes than in rams. These results suggest that in sheep stress reduces responsiveness of the pituitary gland to exogenous GnRH during the nonbreeding season but not during the breeding season, possibly because of mediators of the stress response other than those of the hypothalamus-pituitary-adrenal gland axis.
应激反应被认为是在下丘脑 - 垂体单位内发挥作用，损害生殖系统，并且其作用部位可能因性别而异。研究了隔离和束缚应激对绵羊垂体对促性腺激素释放激素（GnRH）反应性的影响，重点关注可能的性别差异。实验在繁殖季节和非繁殖季节进行。在两个实验中，在3个实验日，每隔2小时静脉注射125 ng GnRH到下丘脑 - 垂体分离、性腺切除的公羊和母羊体内，每天分为两个时间段。在第2天的第二个时间段，施加5.5小时的隔离和束缚应激。从颈静脉采集的血样中测量促黄体生成素（LH）和皮质醇的血浆浓度。在第二个实验（非繁殖季节）中，还测量了肾上腺素、去甲肾上腺素、3,4 - 二羟基苯丙氨酸和3,4 - 二羟基苯乙二醇的血浆浓度。在两个实验中，隔离和束缚应激对两性的皮质醇血浆浓度均无影响。在繁殖季节，隔离和束缚应激对两性的LH血浆浓度均无影响。在非繁殖季节，应激开始后公羊和母羊的第一个LH脉冲幅度显著降低（P < 0.05）。在第二个实验中，应激期间公羊和母羊的肾上腺素血浆浓度显著升高（P < 0.05），并且母羊的去甲肾上腺素基础浓度显著高于公羊（P < 0.05）。这些结果表明，在绵羊中，应激在非繁殖季节会降低垂体对外源性GnRH的反应性，但在繁殖季节不会，这可能是由于应激反应的介质不是下丘脑 - 垂体 - 肾上腺轴的介质。
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