Hinshelwood M M, Dierschke D J, Hauser E R
Biol Reprod. 1985 Mar;32(2):290-300. doi: 10.1095/biolreprod32.2.290.
Thirty-two postpartum (PP) cows were used to investigate the effect of suckling on secretion of luteinizing hormone (LH). Calves remained with their dams (suckled; S), or they were removed within 24 h of birth (nonsuckled; NS). To evaluate the relationship between suckling and negative feedback regulation of LH, cows were ovariectomized on Day 5 PP, then injected intravenously with estradiol-17 beta (E) or vehicle (V) on Day 10 PP. To investigate the influence of suckling on the gonadotropin-releasing hormone (GnRH)-induced release of LH, cows were injected with 80 micrograms of GnRH on a single day varying from 18 to 85 days PP. Suckling inhibited the postcastration rise in LH, as LH concentrations increased at a faster rate in NS compared with S cows [0.031 +/- 0.02 ng/(ml X day) LH: P less than 0.05]; this was not influenced by basal amounts of E since amounts did not differ between S and NS cows at ovariectomy (5.37 +/- 0.36 vs. 5.34 +/- 0.48 pg/ml E; P greater than 0.05). Serum concentrations of LH were negatively related to total follicular E only in S cows (r = -0.71; P less than 0.01). Estradiol-17 beta caused a decrease not only in the level but also the variability in LH concentrations in both S and NS cows: LH in S cows was less variable after E than in NS cows (P less than 0.001), but the magnitude of LH suppression was not influenced by suckling (P greater than 0.25). The regression of LH response on days PP was essentially the same over time for both S (P greater than 0.25) and NS (P greater than 0.25) cows, indicating that LH response to a GnRH injection was not influenced by suckling or days PP. Suckled cows had a tendency to release more LH relative to their baseline in response to GnRH as time PP increased (P less than 0.10), but NS cows did not. These results indicate that even though ovarian secretions inhibit LH release from the pituitary, other inhibitory influences may have a major effect in S cows. Concentrations of LH were lower in S cows than NS cows on Day 10 PP, following removal of the ovaries on Day 5, suggesting that suckling had a direct effect on the hypothalamic-pituitary axis.
32头产后奶牛用于研究哺乳对促黄体生成素（LH）分泌的影响。犊牛与它们的母亲待在一起（哺乳组；S），或者在出生后24小时内被移走（非哺乳组；NS）。为了评估哺乳与LH负反馈调节之间的关系，奶牛在产后第5天进行卵巢切除，然后在产后第10天静脉注射17β-雌二醇（E）或溶剂（V）。为了研究哺乳对促性腺激素释放激素（GnRH）诱导的LH释放的影响，在产后18至85天的某一天给奶牛注射80微克GnRH。哺乳抑制了去势后LH的升高，因为与哺乳组奶牛相比，非哺乳组奶牛的LH浓度升高速度更快[LH：0.031±0.02 ng/（ml·天）；P<0.05]；这不受基础E量的影响，因为在卵巢切除时，哺乳组和非哺乳组奶牛的E量没有差异（5.37±0.36 vs.5.34±0.48 pg/ml E；P>0.05）。仅在哺乳组奶牛中，LH的血清浓度与卵泡总E呈负相关（r = -0.71；P<0.01）。17β-雌二醇不仅导致哺乳组和非哺乳组奶牛LH浓度水平降低，还导致其变异性降低：E处理后，哺乳组奶牛的LH变异性低于非哺乳组奶牛（P<0.001），但LH抑制的幅度不受哺乳影响（P>0.25）。随着产后天数的增加，哺乳组（P>0.25）和非哺乳组（P>0.25）奶牛LH反应的回归在本质上是相同的，这表明LH对GnRH注射的反应不受哺乳或产后天数的影响。随着产后天数的增加，哺乳组奶牛对GnRH的反应相对于其基线有释放更多LH的趋势（P<0.10），而非哺乳组奶牛则没有。这些结果表明，即使卵巢分泌物抑制垂体释放LH，但其他抑制性影响可能对哺乳组奶牛有主要作用。在产后第5天切除卵巢后，产后第10天哺乳组奶牛的LH浓度低于非哺乳组奶牛，这表明哺乳对下丘脑-垂体轴有直接影响。
