Jo M, Fortune J E
Department of Biomedical Sciences, College of Veterinary Medicine, T6-012B VRT, Cornell University, Ithaca, NY 14853, USA.
Mol Cell Endocrinol. 2003 Feb 28;200(1-2):31-43. doi: 10.1016/s0303-7207(02)00418-5.
In cattle, production of oxytocin by granulosa cells of preovulatory follicles is induced by the LH/FSH surge and intrafollicular oxytocin increases dramatically toward the end of the interval between the surge and ovulation. We reported previously that oxytocin modulates steroid production by both theca and granulosa cells obtained from bovine preovulatory follicles, implying actions of oxytocin on both cell types of preovulatory follicles. The objective of the present study was to examine the temporal expression of oxytocin receptor mRNA and protein in both theca and granulosa cells of bovine periovulatory follicles. To induce luteal regression and initiate a follicular phase, heifers were injected with prostaglandin F(2alpha) on Day 6 or 7 of the estrous cycle and 36 h later, a GnRH analogue was administered to induce the LH/FSH surge. The periovulatory follicle was isolated at 0, 3.5, 12, or 24 h after GnRH injection. A significant increase in the levels of mRNA for oxytocin was detected in granulosa, but not theca, cells of periovulatory follicles at 12 and 24 h after GnRH injection, relative to time 0. In contrast, the levels of oxytocin receptor mRNA and specific binding sites for oxytocin in granulosa cells had decreased significantly at 12 and 24 h post-GnRH. In theca cells, the levels of oxytocin receptor mRNA were significantly lower at 12 and 24 h compared with values at 3.5 h, but specific binding of oxytocin to thecal cell membranes was not different at any time point. Immunopositive staining for oxytocin receptor was localized to both the theca and granulosa cell layer of periovulatory follicles at all four times of follicle isolation. These results suggest the direct action of oxytocin on both theca and granulosa cells of bovine periovulatory follicles through binding to its receptor, supporting the hypothesis that follicular oxytocin plays an important role(s) in the regulation of the final stage of follicular development. Down-regulation of oxytocin receptor mRNA and oxytocin binding may serve to temporally limit the actions of oxytocin on the preovulatory follicle.
在牛中，排卵前卵泡颗粒细胞产生催产素是由促黄体生成素/促卵泡激素高峰诱导的，并且卵泡内催产素在高峰与排卵之间的间隔末期会急剧增加。我们之前报道过，催产素可调节从牛排卵前卵泡获得的卵泡膜细胞和颗粒细胞的类固醇生成，这意味着催产素对排卵前卵泡的两种细胞类型均有作用。本研究的目的是检测牛排卵前后卵泡的卵泡膜细胞和颗粒细胞中催产素受体mRNA和蛋白质的时间表达情况。为诱导黄体退化并启动卵泡期，在发情周期的第6天或第7天给小母牛注射前列腺素F(2α)，36小时后，给予促性腺激素释放激素类似物以诱导促黄体生成素/促卵泡激素高峰。在注射促性腺激素释放激素后0、3.5、12或24小时分离排卵前后卵泡。与0小时相比，在注射促性腺激素释放激素后12小时和24小时，排卵前后卵泡的颗粒细胞中检测到催产素mRNA水平显著增加，但卵泡膜细胞中未检测到。相反，在促性腺激素释放激素注射后12小时和24小时，颗粒细胞中催产素受体mRNA水平和催产素特异性结合位点显著降低。在卵泡膜细胞中，与3.5小时的值相比，12小时和24小时的催产素受体mRNA水平显著降低，但在任何时间点，催产素与卵泡膜细胞膜的特异性结合均无差异。在卵泡分离的所有四个时间点，排卵前后卵泡的卵泡膜细胞层和颗粒细胞层均检测到催产素受体免疫阳性染色。这些结果表明，催产素通过与其受体结合直接作用于牛排卵前后卵泡的卵泡膜细胞和颗粒细胞，支持了卵泡内催产素在卵泡发育最后阶段的调节中起重要作用的假说。催产素受体mRNA和催产素结合的下调可能在时间上限制了催产素对排卵前卵泡的作用。
