Gümen Ahmet, Wiltbank Milo C
Department of Dairy Science, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Biol Reprod. 2002 Jun;66(6):1689-95. doi: 10.1095/biolreprod66.6.1689.
Many mammals, including cattle, can develop ovarian follicular cysts, but the physiological mechanisms leading to this condition remain undefined. We hypothesized that follicular cysts can develop because estradiol will induce a GnRH/LH surge on one occasion but progesterone exposure is required before another GnRH/LH surge can be induced by estradiol. In experiment 1, 14 cows were synchronized with an intravaginal progesterone insert (IPI) for 7 days, and prostaglandin F(2alpha) was given on the day of IPI removal. Estradiol benzoate (EB; 5 mg i.m.) was given 3 days before IPI removal to induce atresia of follicles. Cows were given a second EB treatment 1 day after IPI removal to induce a GnRH/LH surge in the absence of an ovulatory follicle. All cows had an LH surge following the second EB treatment, and 10 of 14 cows developed a large-follicle anovulatory condition (LFAC) that resembled follicular cysts. These LFAC cows were given a third EB treatment 15 days later, and none of the cows had an LH surge or ovulation. Cows were then either not treated (control, n = 5) or treated for 7 days with an IPI (n = 5) starting 7 days after the third EB injection. Cows were treated for a fourth time with 5 mg of EB 12 h after IPI removal. All IPI-treated, but no control, cows had an LH surge and ovulated in response to the estradiol challenge. In experiment 2, cows were induced to LFAC as in experiment 1 and were then randomly assigned to one of four treatments 1) IPI + EB, 2) IPI + GnRH (100 microg), 3) control + EB, and 4) control + GnRH. Control and IPI-treated cows had a similar LH surge and ovulation when treated with GnRH. In contrast, only IPI-treated cows had an LH surge following EB treatment. Thus, an initial GnRH/LH surge can be induced with high estradiol, but estradiol induction of a subsequent GnRH/LH surge requires exposure to progesterone. This effect is mediated by the hypothalamus, as evidenced by similar LH release in response to exogenous GnRH. This may represent the physiological condition that underlies ovarian follicular cysts.
包括牛在内的许多哺乳动物都会出现卵巢卵泡囊肿，但导致这种情况的生理机制仍不明确。我们推测卵泡囊肿的形成是因为雌二醇在某一时刻会诱导促性腺激素释放激素/促黄体生成素激增，但在雌二醇能够诱导下一次促性腺激素释放激素/促黄体生成素激增之前，需要接触孕酮。在实验1中，14头母牛通过阴道内孕酮植入物（IPI）同步发情7天，并在取出IPI当天给予前列腺素F（2α）。在取出IPI前3天给予苯甲酸雌二醇（EB；5毫克，肌肉注射）以诱导卵泡闭锁。在取出IPI后1天对母牛进行第二次EB处理，以在没有排卵卵泡的情况下诱导促性腺激素释放激素/促黄体生成素激增。所有母牛在第二次EB处理后都出现了促黄体生成素激增，14头母牛中有10头出现了类似卵泡囊肿的大卵泡无排卵状态（LFAC）。15天后对这些LFAC母牛进行第三次EB处理，没有一头母牛出现促黄体生成素激增或排卵。然后，母牛要么不进行处理（对照组，n = 5），要么在第三次EB注射7天后开始用IPI处理7天（n = 5）。在取出IPI后12小时，对母牛进行第四次5毫克EB处理。所有接受IPI处理的母牛，但对照组没有，在接受雌二醇刺激后都出现了促黄体生成素激增并排卵。在实验2中，母牛如实验1那样被诱导进入LFAC状态，然后随机分配到四种处理之一：1）IPI + EB，2）IPI + 促性腺激素释放激素（100微克），3）对照组 + EB，4）对照组 + 促性腺激素释放激素。当用促性腺激素释放激素处理时，对照组和接受IPI处理的母牛的促黄体生成素激增和排卵情况相似。相比之下，只有接受IPI处理的母牛在接受EB处理后出现了促黄体生成素激增。因此，高剂量雌二醇可诱导初始促性腺激素释放激素/促黄体生成素激增，但雌二醇诱导后续促性腺激素释放激素/促黄体生成素激增需要接触孕酮。这种效应由下丘脑介导，对外源促性腺激素释放激素的反应中促黄体生成素释放相似证明了这一点。这可能代表了卵巢卵泡囊肿背后的生理状况。
