Funston R N, Moss G E, Roberts A J
University of Wyoming, Laramie 82071.
Endocrinology. 1995 Jan;136(1):62-8. doi: 10.1210/endo.136.1.7530196.
The objective of this study was to determine whether concentrations of hypophyseal and serum insulin-like growth factor-I (IGF-I) and binding activities of serum and hypophyseal IGF-binding proteins (IGFBPs) differ with stage of the estrous cycle in mature beef cows. Cows were assigned to the following stages of the estrous cycle based on serum concentrations of progesterone (P4) and ovarian structures at death: days 1-5 (day 0 = estrus; n = 18), days 6-10 (n = 24), days 11-16 (n = 39), and days 17-21 (n = 7). Serum samples collected at death and anterior pituitary homogenates were analyzed for IGF-I, LH, and FSH by RIA. Serum and pituitary IGFBPs were evaluated by ligand and immunoblot analyses. Serum samples contained IGFBP activity at 44 and 40 kilodaltons (kDa; IGFBP-3), 34 kDa (IGFBP-2), 30 kDa (IGFBP-5), 28 kDa, and 24 kDa. The intensity of binding by the different sized proteins in serum remained constant throughout the estrous cycle. IGFBPs detected in anterior pituitaries included a 36-/40-kDa doublet (IGFBP-3), a 32-kDa protein (IGFBP-2), and a 29-kDa IGFBP (IGFBP-5). The intensity of [125I]IGF-I binding to IGFBPs was greater (P < 0.05) during days 11-16 than days 1-5 or days 6-10 of the estrous cycle and was intermediate (P > 0.05) during days 17-21. Serum concentrations of LH were low (< 0.4 ng/ml) during days 1-16 of the estrous cycle, but increased (P < 0.05) approximately 3- to 4-fold during days 17-21. LH concentrations in the anterior pituitary increased (P < 0.05) from the postovulatory period (548 +/- 52 micrograms/g; days 1-5) to the late luteal phase (791 +/- 39 micrograms/g; days 11-16) and were intermediate (P > 0.05) during the preovulatory phase (707 +/- 85 micrograms/g; days 17-21). Concentrations of IGF-I and FSH in the anterior pituitary and serum did not differ (P > 0.05) by stage of the estrous cycle. A positive correlation among the different IGFBPs in the pituitary (P < 0.01) and between each pituitary IGFBP and serum P4 (P < 0.05) existed. The significance (P < 0.0002) of the correlation between pituitary IGFBP-3 and P4 was greater (P < 0.02) than that between the other pituitary IGFBPs and P4. In summary, IGFBP activity in the anterior pituitary, but not that in serum, changed with stage of the estrous cycle in association with serum concentrations of P4. The absence of similar changes in serum or anterior pituitary concentrations of IGF-I supports the hypothesis that IGFBPs may regulate the actions of IGF-I on gonadotropin release from the anterior pituitary gland during the estrous cycle of beef cattle.
本研究的目的是确定成熟肉牛垂体和血清中胰岛素样生长因子-I（IGF-I）的浓度以及血清和垂体中IGF结合蛋白（IGFBPs）的结合活性是否随发情周期阶段而变化。根据死亡时血清孕酮（P4）浓度和卵巢结构，将母牛分为发情周期的以下阶段：第1 - 5天（第0天 = 发情；n = 18），第6 - 10天（n = 24），第11 - 16天（n = 39），以及第17 - 21天（n = 7）。对死亡时采集的血清样本和垂体前叶匀浆进行放射免疫分析（RIA），检测IGF-I、促黄体生成素（LH）和促卵泡生成素（FSH）。通过配体和免疫印迹分析评估血清和垂体中的IGFBPs。血清样本中含有分子量为44和40千道尔顿（kDa；IGFBP-3）、34 kDa（IGFBP-2）、30 kDa（IGFBP-5）、28 kDa和24 kDa的IGFBP活性。在整个发情周期中，血清中不同大小蛋白质的结合强度保持恒定。在垂体前叶中检测到的IGFBPs包括一个36/40-kDa双峰（IGFBP-3）、一个32-kDa蛋白（IGFBP-2）和一个29-kDa的IGFBP（IGFBP-5）。发情周期第11 - 16天期间，[125I]IGF-I与IGFBPs的结合强度大于（P < 0.05）第1 - 5天或第6 - 10天，在第17 - 21天期间处于中间水平（P > 0.05）。发情周期第1 - 16天期间血清LH浓度较低（< 0.4 ng/ml），但在第17 - 21天期间升高（P < 0.05）约3至4倍。垂体前叶中的LH浓度从排卵后期（548 ± 52微克/克；第1 - 5天）到黄体后期（791 ± 39微克/克；第11 - 16天）升高（P < 0.05），在排卵前期（707 ± 85微克/克；第17 - 21天）处于中间水平（P > 0.05）。垂体前叶和血清中IGF-I和FSH的浓度在发情周期各阶段无差异（P > 0.05）。垂体中不同IGFBPs之间存在正相关（P < 0.01），且每个垂体IGFBP与血清P4之间也存在正相关（P < 0.05）。垂体IGFBP-3与P4之间的相关性显著（P < 0.0002），大于（P < 0.02）其他垂体IGFBPs与P4之间的相关性。总之，垂体前叶中的IGFBP活性而非血清中的IGFBP活性随发情周期阶段变化，并与血清P4浓度相关。血清或垂体前叶中IGF-I浓度未出现类似变化支持了以下假说：在肉牛发情周期中，IGFBPs可能调节IGF-I对垂体前叶促性腺激素释放的作用。
