Mechanisms of suppression of gonadotrophins secretion by suckling stimuli in lactating rats.

用隔夜分离的去卵巢哺乳大鼠研究促肾上腺皮质激素释放因子(CRH)和β-内啡肽在抑制哺乳期黄体生成素和卵泡刺激素分泌中的作用。在将幼崽送回母亲身边的1小时内，血浆黄体生成素浓度显着下降，血浆催乳素浓度显着升高。然而，重新哺乳直到产仔后12h才引起血浆FSH浓度的显著变化，但此后显著下降。在清除猫砂24小时后，进行单次静脉注射。在哺乳过程中，注射200mul抗LHRH血清可引起哺乳大鼠血浆中促黄体生成素和卵泡刺激素浓度的类似变化。这些结果表明，哺乳刺激本身通过抑制LHRH的分泌来抑制促黄体生成素和卵泡刺激素。移除猫砂24小时后，单侧脑室(i.c.v.)注射促肾上腺皮质激素释放激素或β-内啡肽均可使血浆黄体生成素迅速下降。在1h内，只有β-内啡肽引起血浆催乳素水平显着升高，而FSH受这两种激素的影响都较小。重复一次静脉注射。每隔6h给药10mug CRH或β-内啡肽，48h内对黄体生成素和卵泡刺激素的分泌均有较长时间的抑制作用，而β-埃立吗啡的抑制作用弱于促肾上腺皮质激素释放激素。结果表明，哺乳刺激对黄体生成素和卵泡刺激素的分泌均有抑制作用，提示这种作用可能是通过抑制下丘脑的促黄体生成素释放来实现的。他们还提示，哺乳对LHRH的抑制可能主要是由内源性CRH和阿片肽介导的。

The roles of corticotrophin-releasing factor (CRH) and beta-endorphin in the suppression of LH and FSH secretion during lactation were investigated using ovariectomized lactating rats separated from their litters overnight. Within 1 h of returning the pups to their mothers a marked fall in plasma LH concentration and a large increase in plasma prolactin were noted. However, resuckling caused no significant change in plasma concentration of FSH until 12 h after the return of the litter but a significant decline occurred thereafter. Twenty-four hours after removal of the litter, a single i.v. injection of 200mul anti-LHRH serum caused similar changes in plasma concentrations of LH and FSH observed in nursing rats during suckling. These results suggest that the suckling stimulus itself is responsible for the suppression of LH as well as FSH, via inhibition of the secretion of LHRH. Twenty-four hours after removal of the litter, a single intracerebroventricular (i.c.v.) injection of either 10mug CRH or beta- endorphin resulted in a rapid decrease in plasma LH. Only beta-endorphin caused a marked increase in plasma levels of prolactin within 1 h whereas FSH was less affected by either hormone. Repeated i.c.v. administration of 10mug CRH or beta-endorphin at 6 h intervals caused a prolonged inhibition of LH as well as FSH secretion during 48 h, with beta-eridorphin being less effective than CRH.These results demonstrate that the suckling stimulus alone suppressed the secretion of both LH and FSH, and suggest that this effect may be mediated by the inhibition of LHRH secretion from the hypothalamus. They also suggest that the suckling-induced inhibition of LHRH may be primarily mediated by endogenous CRH,and opioid peptides.