Department of Obstetrics and Reproduction, Veterinary Faculty, University of Thessaly, Karditsa, Greece.
Theriogenology. 2013 Aug;80(3):262-8. doi: 10.1016/j.theriogenology.2013.04.005. Epub 2013 May 9.
In addition to its metabolic role, ghrelin has been found to suppress luteinizing hormone secretion in many species acting mainly at the hypothalamic level. The objectives of the present study were to test the hypothesis that besides its effects on the hypothalamic level, ghrelin exerts a direct action on the pituitary. Twelve cycling ewes were synchronized, using progestagen intravaginal sponges and superovulated using eCG. At the time of sponge withdrawal, animals were allocated into two groups, ghrelin-treated (Gh) and control. Two days after the sponge removal, GnRH was given to synchronize ovulations. Simultaneously with GnRH treatment, animals of the Gh group received the first of four treatments of acylated human ghrelin at a dose of 6 μg/kg body weight iv; three additional treatments of ghrelin iv were given every 15 minutes thereafter. Control animals received saline iv. Blood samples were collected before challenge (-30 and 0 minutes) and at 30, 60, 75, 90, 105, 120, 135, 150, and 180 minutes after GnRH treatment, and were analyzed for LH, FSH, estradiol, progesterone, insulin, and insulin-like growth factor-I concentrations. Ghrelin treatment attenuated GnRH-induced a preovulatory surge of both gonadotrophins, with the effect being greater for LH. No difference was detected for insulin, estradiol, and progesterone concentrations, and insulin-like growth factor-I levels were increased in the Gh group. Our results imply that in sheep, ghrelin conducts specific regulatory effects on the GnRH/LH axis, and provide for the first time strong evidence that besides its central action, ghrelin might regulate gonadotrophin release acting at the pituitary level.
除了其代谢作用外，生长激素释放肽已被发现可在许多物种中抑制促黄体生成素的分泌，主要作用于下丘脑水平。本研究的目的是检验以下假设，即除了对下丘脑水平的影响外，生长激素释放肽还对垂体发挥直接作用。12 只循环母羊通过阴道内孕激素海绵和 eCG 超排卵来同步。在海绵取出时，将动物分为两组，即生长激素释放肽处理（Gh）组和对照组。海绵取出后两天，给予 GnRH 以同步排卵。在 GnRH 处理的同时，Gh 组的动物接受了四次酰化人生长激素释放肽治疗中的第一次，剂量为 6μg/kg 体重静脉内；此后每 15 分钟给予另外三次生长激素释放肽静脉内治疗。对照组动物接受生理盐水静脉内治疗。在挑战前（-30 和 0 分钟）和 GnRH 处理后 30、60、75、90、105、120、135、150 和 180 分钟收集血液样本，并分析 LH、FSH、雌二醇、孕酮、胰岛素和胰岛素样生长因子-I 浓度。生长激素释放肽处理减弱了 GnRH 诱导的促性腺激素前排卵激增，对 LH 的作用更大。胰岛素、雌二醇和孕酮浓度无差异，Gh 组的胰岛素样生长因子-I 水平升高。我们的结果表明，在绵羊中，生长激素释放肽对 GnRH/LH 轴具有特定的调节作用，并首次提供了强有力的证据，表明除了其中枢作用外，生长激素释放肽可能通过作用于垂体水平来调节促性腺激素的释放。
