Fitzgerald B P, Davison L A
Department of Veterinary Science, Maxwell Gluck Equine Research Center, University of Kentucky, Lexington 40546-0099, USA.
Biol Reprod. 1997 Jul;57(1):36-42. doi: 10.1095/biolreprod57.1.36.
This study investigated the hypothesis that for a subpopulation of horse mares continuation of estrous cycles during the nonbreeding season may be attributed to continued stimulatory glutamatergic activity on GnRH-secreting neurons. The gonadotropin response to the glutamatergic agonist N-methyl-DL-aspartic acid (NMA) was compared in cycling and anestrous mares during the nonbreeding season. It was anticipated that the gonadotropin response to NMA in cycling mares would be attenuated, compared with that of anestrous mares. The experiment used 16 anestrous mares and 15 mares that cycled during the nonbreeding season. The effect of NMA on prolactin secretion was also evaluated. In addition, the seasonal rhythm of prolactin secretion was compared in anestrous and cycling mares during October-April. In cycling mares, the response to NMA was dependent on the stage of the cycle, and a significantly (p < 0.05) larger proportion responded during the luteal phase (6 of 8), compared with the follicular phase (1 of 7 mares). The proportion of anestrous mares that responded to NMA was similar to that of cycling mares during the luteal phase, but larger than during the follicular phase. In anestrous and cycling mares, NMA suppressed prolactin secretion, and in both groups prolactin secretion decreased during the nonbreeding season. Thus, we conclude that differences in reproductive activity in mares during the nonbreeding season are unlikely to reflect a change in glutamatergic activity.
本研究调查了一种假说，即对于一部分母马而言，非繁殖季节发情周期的持续可能归因于对促性腺激素释放激素（GnRH）分泌神经元持续的刺激性谷氨酸能活动。在非繁殖季节，比较了处于发情周期和乏情期的母马对谷氨酸能激动剂N-甲基-DL-天冬氨酸（NMA）的促性腺激素反应。预计与乏情期母马相比，处于发情周期的母马对NMA的促性腺激素反应会减弱。该实验使用了16匹乏情期母马和15匹在非繁殖季节有发情周期的母马。还评估了NMA对催乳素分泌的影响。此外，比较了10月至4月期间乏情期和有发情周期母马催乳素分泌的季节性节律。在有发情周期的母马中，对NMA的反应取决于发情周期阶段，与卵泡期（7匹母马中的1匹）相比，黄体期（8匹中的6匹）有显著更多（p<0.05）的母马有反应。对NMA有反应的乏情期母马比例与黄体期有发情周期的母马相似，但高于卵泡期。在乏情期和有发情周期的母马中，NMA均抑制催乳素分泌，且在非繁殖季节两组母马的催乳素分泌均减少。因此，我们得出结论，母马在非繁殖季节生殖活动的差异不太可能反映谷氨酸能活动的变化。
