Smith M S
Endocrinology. 1982 Mar;110(3):882-91. doi: 10.1210/endo-110-3-882.
The ability of pituitaries from lactating animals to secrete LH and FSH in response to gonadotropin-releasing hormone (GnRH) was studied in vitro using a pituitary incubation system. Hemipituitaries were exposed to GnRH for 6 min during each hour of incubation. LH release by anterior pituitaries (APs) from day 5 postpartum rats nursing eight pups, in response to pulsatile exposure to GnRH, was significantly less than that released by APs from diestrous cycling females. Even though the amount of LH released by APs increased as lactation progressed, LH release by APs from day 15 postpartum rats nursing eight pups was still less than LH release by APs from diestrous females. In contrast pituitaries from lactating females nursing two pups released amounts of LH similar to that released by pituitaries from diestrous females, whereas females deprived of their litters for 48 h showed a greater response than diestrous females. Generally, there was a good quantitative relationship between the amount of LH released in vitro and plasma LH concentrations for all the intact groups studied. The ability of lactation to suppress the postcastration rise in serum LH also was demonstrated in vitro as pituitaries from ovariectomized or intact females nursing eight pups released similar amounts of LH on days 5 and 10 postpartum. However, by day 15 postpartum, even though serum LH concentrations were still very low, pituitaries from ovariectomized lactating females released LH in vitro at a rate similar to pituitaries from nonlactating rats. Serum FSH concentrations were not suppressed but similar in intact and cycling females. Also, the total amount of FSH released in vitro in response to GnRH by pituitaries from lactating and cycling females did not differ significantly, even though LH release differed greatly among these groups of animals. However, the patterns of GnRH-stimulating FSH secretion differed among intact lactating, ovariectomized lactating, and nonlactating females. Pituitary LH concentrations were similar on day 5 postpartum and diestrus and on day 15 postpartum and proestrus. Pituitary FSH concentrations on day 5 postpartum were similar to those during diestrus and proestrus and had increased 2-3 times by day 15 postpartum. Generally, there was no correlation between the amount of LH or FSH released by pituitaries in response to GnRH and pituitary gonadotropin content. In summary, the inability of pituitaries from lactating rats to respond adequately to large doses of GnRH in vitro suggests that the suckling stimulus indirectly suppresses pituitary responsiveness to GnRH. This suppression differentially affects basal LH secretion, but not basal FSH secretion, and may be the direct result of inadequate GnRH stimulation in vivo.
利用垂体孵育系统在体外研究了泌乳动物垂体对促性腺激素释放激素（GnRH）作出反应分泌促黄体生成素（LH）和促卵泡生成素（FSH）的能力。在每小时的孵育过程中，半垂体暴露于GnRH 6分钟。产后第5天哺乳8只幼崽的大鼠的垂体前叶（AP）对GnRH脉冲暴露的反应释放的LH，显著少于处于动情周期的雌性大鼠的垂体前叶释放的LH。尽管随着泌乳的进行，垂体前叶释放的LH量增加，但产后第15天哺乳8只幼崽的大鼠的垂体前叶释放的LH仍少于动情期雌性大鼠的垂体前叶释放的LH。相比之下，哺乳2只幼崽的泌乳雌性大鼠的垂体释放的LH量与动情期雌性大鼠的垂体释放的LH量相似，而剥夺幼崽48小时的雌性大鼠的反应比动情期雌性大鼠更强。一般来说，在所研究的所有完整组中，体外释放的LH量与血浆LH浓度之间存在良好的定量关系。泌乳抑制去势后血清LH升高的能力在体外也得到了证实，因为在产后第5天和第10天，来自切除卵巢或完整的哺乳8只幼崽的雌性大鼠的垂体释放的LH量相似。然而，到产后第15天，尽管血清LH浓度仍然很低，但来自切除卵巢的泌乳雌性大鼠的垂体在体外释放LH的速率与来自非泌乳大鼠的垂体相似。血清FSH浓度未被抑制，在完整和动情周期的雌性大鼠中相似。此外，尽管这些动物组之间LH释放差异很大，但泌乳和动情周期的雌性大鼠的垂体对GnRH反应在体外释放的FSH总量没有显著差异。然而，GnRH刺激FSH分泌的模式在完整泌乳、切除卵巢泌乳和非泌乳雌性大鼠之间有所不同。产后第5天的垂体LH浓度与动情期相似，产后第15天与动情前期相似。产后第5天的垂体FSH浓度与动情期和动情前期相似，到产后第15天增加了2 - 3倍。一般来说，垂体对GnRH反应释放的LH或FSH量与垂体促性腺激素含量之间没有相关性。总之，泌乳大鼠的垂体在体外不能对大剂量GnRH作出充分反应，这表明哺乳刺激间接抑制了垂体对GnRH的反应性。这种抑制对基础LH分泌有不同影响，但对基础FSH分泌没有影响，可能是体内GnRH刺激不足的直接结果。
