Hötzel M J, Walkden-Brown S W, Blackberry M A, Martin G B
Faculty of Agriculture (Animal Science), University of Western Australia, Nedlands, Western Australia.
J Endocrinol. 1995 Oct;147(1):75-85. doi: 10.1677/joe.0.1470075.
In mature Merino rams, changes in diet to below or above the requirements for maintenance of body weight lead to changes in gonadotrophin secretion and testicular growth. However, the effects on testicular growth persist for much longer than those on LH and FSH secretion so that the gonadal and gonadotrophin responses are poorly correlated over time. This suggests that the gonadal effects may be partly independent of changes in the hypothalamic secretion of GnRH, an hypothesis tested in this study. In a short-term experiment (November, late spring, non-breeding season), we tested whether a high frequency of exogenous GnRH pulses could override the endogenous system and mimic the change in gonadotrophins seen in rams fed a high plane of nutrition. Mature Merino rams (scrotal circumference (mean +/- S.E.M.) 33.6 +/- 0.5 cm, body weight (mean +/- S.E.M.) 59.0 +/- 0.9 kg) were fed 900 g chaff + 1.6 kg lupin grain (High diet) or 360 g chaff + 60 g lupin grain (Low diet) and infused with 8 pulses of GnRH or saline daily for 5 weeks (n = 5/group). Blood was sampled every 20 min for 12 h on days-1 and 14 relative to the start of treatments. Relative to pre-treatment levels, LH pulse frequency and FSH concentrations were decreased on day 14 in saline-infused rams fed the Low diet and increased in saline-infused rams fed the High diet (P < 0.001). In GnRH-infused rams, gonadotrophin secretion was not affected by diet and the patterns of secretion of LH and FSH were similar to those in saline-infused rams fed the High diet. This model was used for a more complete endocrine analysis in a longer experiment designed to test the hypothesis that the effect of nutrition on testicular growth is partly independent of changes in the secretion of GnRH. The same treatments were imposed for 35 days on a different group of similar rams in March (autumn, mid-breeding season). Body weight and scrotal circumference were measured weekly and blood was sampled on days -1 and 14. On days -1 and 35, testosterone secretion in response to LH was tested by injecting exogenous ovine LH (NIADDK-oLH-25; 200 ng/kg body weight) to all rams. Body weight increased in rams fed the High diet and decreased in those fed the Low diet (P < 0.001) and was not affected by treatments as in experiment 1.(ABSTRACT TRUNCATED AT 400 WORDS)
在成年美利奴种公羊中，饮食改变至低于或高于维持体重所需水平会导致促性腺激素分泌及睾丸生长发生变化。然而，对睾丸生长的影响持续时间远长于对促黄体生成素（LH）和促卵泡生成素（FSH）分泌的影响，因此随着时间推移，性腺反应与促性腺激素反应之间的相关性较差。这表明性腺效应可能部分独立于下丘脑促性腺激素释放激素（GnRH）分泌的变化，本研究对这一假说进行了验证。在一项短期实验（11月，晚春，非繁殖季节）中，我们测试了高频率的外源性GnRH脉冲是否能超越内源性系统，并模拟营养水平高的公羊中促性腺激素的变化。成年美利奴种公羊（阴囊周长（均值±标准误）33.6±0.5厘米，体重（均值±标准误）59.0±0.9千克）被喂食900克粗饲料+1.6千克羽扇豆谷物（高营养日粮）或360克粗饲料+60克羽扇豆谷物（低营养日粮），并每天注入8次GnRH脉冲或生理盐水，持续5周（每组n = 5只）。在相对于处理开始的第-1天和第14天，每隔20分钟采集一次血液样本，共采集12小时。相对于处理前水平，在第14天，喂食低营养日粮且注入生理盐水的公羊的LH脉冲频率和FSH浓度降低，而喂食高营养日粮且注入生理盐水的公羊的LH脉冲频率和FSH浓度升高（P < 0.001）。在注入GnRH的公羊中，促性腺激素分泌不受饮食影响，LH和FSH的分泌模式与喂食高营养日粮且注入生理盐水的公羊相似。在一项更长的实验中，该模型被用于更全面的内分泌分析，以验证营养对睾丸生长的影响部分独立于GnRH分泌变化这一假说。在3月（秋季，繁殖中期），对另一组相似的公羊进行了35天的相同处理。每周测量体重和阴囊周长，并在第-1天和第14天采集血液样本。在第-1天和第35天，通过给所有公羊注射外源性绵羊LH（美国国立糖尿病、消化和肾脏疾病研究所-oLH-25；200纳克/千克体重）来测试睾酮对LH的反应。喂食高营养日粮的公羊体重增加，喂食低营养日粮的公羊体重下降（P < 0.001），且与实验1一样，体重不受处理影响。（摘要截取自400字）
