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

用去卵巢的泌乳大鼠与窝鼠分离过夜，研究促肾上腺皮质激素释放因子（CRH）和β -内啡肽在泌乳过程中抑制促黄体生成素和促卵泡刺激素分泌中的作用。在将幼崽送回母鼠1小时内，血浆LH浓度显著下降，血浆催乳素显著升高。然而，断奶后12小时，血浆FSH浓度才发生显著变化，但此后出现明显下降。取窝24小时后，单次静脉注射200毫升抗lhrh血清，在哺乳期大鼠血浆LH和FSH浓度的变化类似。这些结果表明，哺乳刺激本身通过抑制LHRH的分泌来抑制LH和FSH。取下幼崽24小时后，单次脑室内注射10杯CRH或β -内啡肽可导致血浆LH迅速下降。只有-内啡肽在1小时内引起血浆泌乳素水平的显著增加，而FSH受这两种激素的影响较小。每隔6小时给药10杯CRH或β -内啡肽可在48小时内延长LH和FSH分泌的抑制时间，β -内啡肽的抑制效果不如CRH。这些结果表明，单独的哺乳刺激抑制了黄体生成素和卵泡刺激素的分泌，并提示这种作用可能是通过抑制下丘脑的LHRH分泌介导的。他们还认为，哺乳诱导的LHRH抑制可能主要由内源性CRH和阿片肽介导。

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.