Concannon P W, Roberts P, Graham L, Tennant B C
Department of Physiology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
J Reprod Fertil. 1998 Nov;114(2):299-305. doi: 10.1530/jrf.0.1140299.
Testosterone and LH concentrations were determined in serum samples obtained before and 15 min after injections of GnRH (1 microgram kg-1) administered at 4-7 week intervals over 20 months to groups of male woodchucks (n = 6-7) born and maintained in Northern Hemisphere (boreal) versus Southern Hemisphere (austral) simulated natural photoperiods, beginning at 18-24 months of age. Nadir and peak unstimulated testosterone (0.1 +/- 0.01 and 7.0 +/- 0.1 ng ml-1, respectively) and LH (0.8 +/- 0.2 and 8.1 +/- 1.1 ng ml-1, respectively) concentrations did not differ in boreal versus austral males. In the five boreal and five austral males that were confirmed to be photoentrained, basal (pre-GnRH) concentrations of LH and testosterone were lowest in summer, increased simultaneously in late autumn or early winter, and declined in the spring. GnRH stimulated some LH release throughout the year except for a 1-4 month period in the summer. The initial annual increase in the LH response to GnRH occurred in early autumn, and in 17 of 20 cycles it occurred 1-2 months before the initial increase in basal LH was detected. In the three free-running males not entrained to the photoperiod, the endocrine patterns were similar but were advanced by several months. The results demonstrate that in woodchucks there is a late autumn increase in LH secretion associated with the onset of testicular recrudescence, and an early autumn increase in pituitary response to GnRH before a detectable increase in serum testosterone.
对出生并饲养在北半球（寒带）和南半球（温带）模拟自然光照周期下的雄性土拨鼠（每组6 - 7只），从18 - 24月龄开始，每隔4 - 7周注射促性腺激素释放激素（GnRH，1微克/千克），在注射前和注射后15分钟采集血清样本，测定睾酮和促黄体生成素（LH）浓度。寒带和温带雄性土拨鼠的睾酮（分别为0.1±0.01和7.0±0.1纳克/毫升）和LH（分别为0.8±0.2和8.1±1.1纳克/毫升）的最低和最高基础浓度无差异。在被证实已适应光照周期的5只寒带和5只温带雄性土拨鼠中，LH和睾酮的基础（GnRH注射前）浓度在夏季最低，在深秋或初冬同时升高，在春季下降。除夏季1 - 4个月外，GnRH全年均可刺激一定程度的LH释放。LH对GnRH反应的年度初始增加发生在初秋，在20个周期中的17个周期中，该增加发生在基础LH初始增加被检测到之前的1 - 2个月。在3只未适应光照周期的自由活动雄性土拨鼠中，内分泌模式相似，但提前了几个月。结果表明，在土拨鼠中，LH分泌在深秋增加，与睾丸复壮的开始相关，垂体对GnRH的反应在血清睾酮可检测到增加之前的初秋增加。
