Lado-Abeal J, Lukyanenko Y O, Swamy S, Hermida R C, Hutson J C, Norman R L
Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.
Clin Endocrinol (Oxf). 1999 Jul;51(1):41-51. doi: 10.1046/j.1365-2265.1999.00727.x.
Although the adipocyte protein leptin has been implicated in the control of reproductive function in rodents, its role in primate reproductive physiology is poorly understood. Because primates in puberty show nighttime LH secretion and there is considerable evidence that the fertile state requires adequate nutrition, we reasoned that animals on the verge of reproductive competence would respond to leptin infusions by secreting LH. Food restriction reduces circulating leptin levels and slows or stops the GnRH pulse generator. Therefore, we examined the endocrine effects of leptin infusions in food-restricted male pubertal primates during the night when they normally secrete LH. In addition, we investigated the effect of leptin on in vitro testosterone production by Leydig cells.
Four pubertal male rhesus macaques (Macaca mulatta), 4-5.5 kg in weight (2.5-4-year-old) were examined in this study. Leydig cells from adult male rats were to investigate in vitro effects of leptin.
To document that animals had entered puberty, blood samples were collected from each of the four animals at 15-minute intervals for 15 h both during the day and at night. Since at this age animals secrete LH mainly at night, blood samples were collected at 15-minute intervals from each of the four animals on two separate occasions for 15 h between 1500 and 0600h. During the experiment, animals were feeding from 0800 to 0830h, cages were completely cleaned of food at 0900h and the afternoon meal was not given to individual animals on the day they were studied. One of the studies served as the control (food restricted group) and during the other, 2 mg (n = 4) or 0.3 mg (n = 3) of recombinant human leptin was administered intravenously during 2000-0100h (food restricted plus leptin group). Blood samples (1 ml) were collected through the indwelling catheter and immediately transferred from the plastic syringe into chilled glass tubes containing 10 microl 14% EDTA. The samples were centrifuged at 5-h intervals and the plasma withdrawn and stored frozen at - 20 degrees C in polypropylene vials until assays were performed.
Bioactive LH was determined and testosterone, cortisol and leptin were measured by radioimmunoassay.
During daytime experiments in these animals, LH pulses were sometimes observed late in the day and generally continued for 12-15 h. Food-restricted pubertal males showed delayed or absent LH pulses. Short-term leptin administration to food-restricted male rhesus macaques had no effect on LH, testosterone, or cortisol levels either during or after the infusion. Leptin also had no direct effect on basal or LH-stimulated testosterone production in Leydig cells.
Our data support the notion that leptin is not the missing signal for the acute suppression of reproductive hormones secretion in food-restricted primates.
尽管脂肪细胞蛋白瘦素已被证明与啮齿动物生殖功能的调控有关，但其在灵长类动物生殖生理学中的作用仍知之甚少。由于青春期的灵长类动物会在夜间分泌促黄体生成素（LH），且有大量证据表明生育状态需要充足的营养，我们推测处于生殖能力临界状态的动物会通过分泌LH对瘦素输注做出反应。食物限制会降低循环中的瘦素水平，并减缓或停止促性腺激素释放激素（GnRH）脉冲发生器的活动。因此，我们研究了在夜间正常分泌LH时，对食物限制的青春期雄性灵长类动物进行瘦素输注的内分泌效应。此外，我们还研究了瘦素对睾丸间质细胞体外睾酮生成的影响。
本研究检测了4只青春期雄性恒河猴（猕猴属），体重4 - 5.5千克（2.5 - 4岁）。使用成年雄性大鼠的睾丸间质细胞来研究瘦素的体外效应。
为证明动物已进入青春期，在白天和夜间每隔15分钟从这4只动物身上采集血样，持续15小时。由于这个年龄段的动物主要在夜间分泌LH，所以在1500至0600时之间的两个不同时间段，每隔15分钟从这4只动物身上采集血样，持续15小时。实验期间，动物在0800至0830时进食，0900时将笼内食物彻底清理干净，在进行研究的当天不给个别动物提供午餐。其中一项研究作为对照（食物限制组），另一项研究中，在2000 - 0100时给动物静脉注射2毫克（n = 4）或0.3毫克（n = 3）重组人瘦素（食物限制加瘦素组）。通过留置导管采集血样（1毫升），并立即从塑料注射器转移至含有10微升14%乙二胺四乙酸（EDTA）的冷冻玻璃管中。每隔5小时对样本进行离心，取出血浆并储存在聚丙烯小瓶中，于 - 20℃冷冻保存，直至进行检测。
测定生物活性LH，并通过放射免疫分析法测量睾酮、皮质醇和瘦素。
在这些动物的白天实验中，有时会在当天晚些时候观察到LH脉冲，且通常持续12 - 15小时。食物限制的青春期雄性动物LH脉冲延迟或缺失。对食物限制的雄性恒河猴短期给予瘦素，在输注期间或之后对LH、睾酮或皮质醇水平均无影响。瘦素对睾丸间质细胞的基础睾酮生成或LH刺激的睾酮生成也无直接影响。
我们的数据支持这样一种观点，即瘦素并非食物限制的灵长类动物生殖激素分泌急性抑制所缺失的信号。
