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

采用与窝仔分离过夜的去卵巢哺乳大鼠，研究了促肾上腺皮质激素释放因子（CRH）和β-内啡肽在哺乳期LH和FSH分泌抑制中的作用。在1小时内返回幼仔给他们的母亲，血浆LH浓度显着下降，血浆催乳素大幅增加。然而，复乳导致FSH的血浆浓度没有显着变化，直到12小时后返回的窝，但此后发生了显着下降。取出窝仔后24小时，单次静脉注射200 μ l抗LHRH血清引起哺乳期大鼠中观察到的LH和FSH血浆浓度的相似变化。这些结果表明，哺乳刺激本身是负责抑制LH以及FSH，通过抑制LHRH的分泌。取出窝仔后24小时，单次脑室内（i. c. v.）注射10 μ g CRH或β-内啡肽导致血浆LH迅速下降。只有β-内啡肽引起1小时内催乳素的血浆水平显着增加，而FSH受任何激素的影响较小。重复i. c. v.给药10 mug CRH或β-内啡肽在6小时的间隔造成了长期的抑制LH以及FSH的分泌在48小时内，与β-eridorphin是有效性低于CRH。这些结果表明，单独的哺乳刺激抑制LH和FSH的分泌，并建议，这种效果可能是由下丘脑的LHRH分泌的抑制介导的。他们还表明，吸吮诱导的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.