Smith M S
Endocrinology. 1985 May;116(5):1826-34. doi: 10.1210/endo-116-5-1826.
Anterior pituitaries (APs) from lactating rats were studied in vitro to determine the mechanisms by which LH release, but not FSH release, is suppressed. Hemipituitaries were exposed for 4 h to GnRH (20 nM) or elevated potassium (K+; 57 mM) according to two different regimens: 6 min/h (pulsatile) or 60 min/h (continuous). Pulsatile K+ exposure stimulated similar amounts of LH release by APs from diestrous females and lactating females on day 5 or 10 who were nursing two or eight pups. Pulsatile GnRH stimulation resulted in significantly greater amounts of LH release from all groups than was observed after pulsatile K+, except by APs from females nursing eight pups. In this group, GnRH was no more effective than K+ in stimulating LH release by APs from day 5 of lactation, but was slightly but significantly more effective on APs from day 10 of lactation. The degree of suppression of GnRH-stimulated LH release was directly correlated with the intensity of the suckling stimulus, and removal of the eight-pup suckling stimulus for 48 h completely restored the LH response to GnRH to the response observed by APs from females on diestrous day 2. Exposure of the APs continuously to either K+ or GnRH produced results that were similar to those observed after the pulsatile regimen, except that the total amount of LH released during the 4-h incubation was greater. However, APs from females suckling eight pups still released significantly less LH in response to GnRH than did APs from females suckling two pups or diestrous females. FSH secretion by the APs was similar in response to either pulsatile K+ or GnRH stimulation and was not suppressed by suckling of a large litter. The total amount of FSH released by pituitaries from lactating and cycling animals did not differ significantly, except that by APs females deprived of their eight-pup litters for 48 h, in which case pulsatile GnRH stimulated a greater amount of FSH release. However, the pattern of FSH release varied, in that pulsatile GnRH stimulation of diestrous pituitaries showed a priming response, whereas no priming response was evident during lactation. Exposure of APs to elevated K+ continuously produced little more FSH release than exposure to pulsatile K+ stimulation. However, continuous stimulation by GnRH generally released more FSH than did K+. FSH responses to GnRH by pituitaries from lactating females were similar or greater than the FSH responses by pituitaries from diestrous females.(ABSTRACT TRUNCATED AT 400 WORDS)
对哺乳期大鼠的垂体前叶进行体外研究，以确定促黄体生成素（LH）释放受到抑制而促卵泡生成素（FSH）释放未受抑制的机制。根据两种不同方案，将垂体半叶分别暴露于促性腺激素释放激素（GnRH，20 nM）或高钾（K⁺，57 mM）中4小时：每小时6分钟（脉冲式）或每小时60分钟（持续式）。脉冲式K⁺暴露刺激动情间期雌性大鼠以及哺乳期第5天或第10天哺育2只或8只幼崽的雌性大鼠的垂体前叶释放相似量的LH。除了哺育8只幼崽的雌性大鼠的垂体前叶外，脉冲式GnRH刺激导致所有组释放的LH量均显著高于脉冲式K⁺刺激后观察到的量。在该组中，GnRH在刺激哺乳期第5天雌性大鼠的垂体前叶释放LH方面并不比K⁺更有效，但在刺激哺乳期第10天雌性大鼠的垂体前叶时则略有但显著更有效。GnRH刺激的LH释放受抑制程度与哺乳刺激强度直接相关，去除8只幼崽的哺乳刺激48小时后，LH对GnRH的反应完全恢复到动情期第2天雌性大鼠的垂体前叶所观察到的反应。垂体前叶持续暴露于K⁺或GnRH产生的结果与脉冲式方案后观察到的结果相似，只是在4小时孵育期间释放的LH总量更多。然而，哺育8只幼崽的雌性大鼠的垂体前叶对GnRH的反应释放的LH仍显著少于哺育2只幼崽的雌性大鼠或动情间期雌性大鼠的垂体前叶。垂体前叶对脉冲式K⁺或GnRH刺激的FSH分泌相似，且不受大量幼崽哺乳的抑制。哺乳期和动情周期动物的垂体释放的FSH总量无显著差异，除了剥夺8只幼崽48小时的雌性大鼠的垂体前叶，在这种情况下脉冲式GnRH刺激释放更多的FSH。然而，FSH释放模式有所不同，即脉冲式GnRH刺激动情期垂体显示出启动反应，而哺乳期则无明显启动反应。垂体前叶持续暴露于高K⁺产生的FSH释放量仅略高于脉冲式K⁺刺激。然而，GnRH持续刺激通常比K⁺释放更多的FSH。哺乳期雌性大鼠垂体对GnRH的FSH反应与动情间期雌性大鼠垂体的FSH反应相似或更大。（摘要截取自400字）
