Funston R N, Seidel G E, Klindt J, Roberts A J
Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins 80523, USA.
Biol Reprod. 1996 Dec;55(6):1390-6. doi: 10.1095/biolreprod55.6.1390.
Previous studies have shown that concentrations of insulin-like growth factor (IGF)-binding proteins (BPs) in bovine follicles before the preovulatory surge of LH are inversely associated with estradiol concentrations, such that decreases in IGFBPs occur with advanced development of antral follicles and atresia is associated with increases in IGFBPs. In the present study, we evaluated serum and follicular fluid at different times after the preovulatory surge of LH to determine whether changes in IGF-I and IGFBPs are associated with the marked changes in the steroidogenic capacity that occur in follicle during this period. Serum and fluid from small follicles (> or = 5-mm diameter) and the preovulatory follicle were collected from cows at the onset of standing estrus or 8.5 and 20.5 h after administration of 100 micrograms GnRH at the onset of estrus (n = 4/time). Concentrations of IGF-I (determined by RIA) did not differ (p > 0.10) among times but were lower (p < 0.05) in fluid from small and preovulatory follicles than those in serum. Profiles of IGFBPs (evaluated by ligand blot analysis) differed among serum and fluid from small and preovulatory follicles. Preovulatory follicles contained IGFBP-3 with little or no other IGFBPs detected. Amount of IGFBP-3 and progesterone did not differ with time of sample collection, but a 13- to 15-fold reduction in estradiol-17 beta and androstenedione occurred between 8.5 and 20.5 h after the LH surge. Small follicles contained IGFBP-2, -3, -4, and -5 (determined by immunoprecipitation). The amount of 28-29-kDa IGFBPs (small form of IGFBP-5 and [or] glycosylated form of IGFBP-4) was inversely associated with concentrations of androstenedione. The 31-kDa form of IGFBP-5 was positively correlated with concentration of progesterone. Serum contained IGFBP-2, -3, and -4, but not IGFBP-5. Circulating IGFBP-2, but not other IGFBPs, decreased by 50% from estrus to 20.5 h after GnRH. In summary, amounts of IGF-I or IGFBPs in preovulatory follicular fluid did not change in response to an LH surge, even though estradiol and androstenedione decreased markedly. The absence of IGFBPs other than IGFBP-3 in bovine preovulatory follicles may allow for increased availability of IGF-I, which is proposed to be important for oocyte maturation and ovulation.
以往的研究表明，在促黄体生成素（LH）排卵前激增之前，牛卵泡中胰岛素样生长因子（IGF）结合蛋白（BP）的浓度与雌二醇浓度呈负相关，即随着窦状卵泡的进一步发育，IGFBPs浓度降低，而闭锁则与IGFBPs浓度升高有关。在本研究中，我们评估了LH排卵前激增后不同时间的血清和卵泡液，以确定IGF-I和IGFBPs的变化是否与在此期间卵泡中发生的类固醇生成能力的显著变化相关。在发情开始时或发情开始时注射100微克GnRH后8.5小时和20.5小时，从奶牛身上收集小卵泡（直径≥5毫米）和排卵前卵泡的血清和卵泡液（每次n = 4）。IGF-I的浓度（通过放射免疫分析测定）在不同时间之间没有差异（p>0.10），但小卵泡和排卵前卵泡的卵泡液中的浓度低于血清中的浓度（p<0.05）。IGFBPs的谱图（通过配体印迹分析评估）在小卵泡和排卵前卵泡的血清和卵泡液之间有所不同。排卵前卵泡含有IGFBP-3，几乎没有或没有检测到其他IGFBPs。IGFBP-3的量和孕酮与样本采集时间无关，但在LH激增后8.5至20.5小时之间，雌二醇-17β和雄烯二酮降低了13至15倍。小卵泡含有IGFBP-2、-3、-4和-5（通过免疫沉淀测定）。28-29 kDa的IGFBPs（IGFBP-5的小形式和/或IGFBP-4的糖基化形式）的量与雄烯二酮的浓度呈负相关。IGFBP-5的31 kDa形式与孕酮浓度呈正相关。血清含有IGFBP-2、-3和-4，但不含有IGFBP-5。从发情到GnRH后20.5小时，循环中的IGFBP-2（而非其他IGFBPs）降低了50%。总之，尽管雌二醇和雄烯二酮显著降低，但排卵前卵泡液中IGF-I或IGFBPs的量并未因LH激增而改变。牛排卵前卵泡中除IGFBP-3外不存在其他IGFBPs，这可能会增加IGF-I的可用性，而IGF-I被认为对卵母细胞成熟和排卵很重要。
