Lu J K, LaPolt P S, Nass T E, Matt D W, Judd H L
Endocrinology. 1985 May;116(5):1953-9. doi: 10.1210/endo-116-5-1953.
The progressive cessation of regular ovulatory function in aging female rats is preceded by a significant decrease in the magnitude of the proestrous LH surge during regular estrous cycles. However, our recent study has demonstrated that normal LH secretion and regular estrous cycles can be maintained for an extended period of time in aging females housed with fertile males and allowed to undergo repeated pregnancies. Since progesterone (P) secretion is persistently increased in pregnant rats, the present study examined whether repeated increases in circulating progesterone accounted for these results. Starting at 8 months of age and continuing to 13 months, multiparous rats were grouped and treated as follows: controls: females were housed five per cage; mated: five females were housed with one fertile male and allowed to undergo repeated pregnancies; and P-implanted: females were housed five per cage and implanted sc with Silastic capsules containing P for 3 of every 4 weeks. During the 4.5 months of study, serum concentrations of estradiol (E2) in the P-implanted rats remained between 13 and 27 pg/ml, similar to levels in pregnant females (8-26 pg/ml) of the mated group. These E2 values were less than the preovulatory increase in serum E2 on proestrus (mean +/- SE, 56 +/- 10 pg/ml) in cyclic control females. In contrast, serum P values were persistently elevated in both the pregnant and the P-implanted rats, although the values in the latter (27-55 ng/ml) were about one third to one half of those in the former group (117-125 ng/ ml). All treatments were stopped at 13 months of age, and estrous cycle patterns were determined thereafter. Between 13 and 17 months of age, the percentages of regularly cycling rats were significantly (P less than 0.01) greater in the mated group (50%, 36%, and 15% at 13, 15, and 17 months, respectively) than in the control group (23%, 20%, and 9%, respectively). During this same period, 50% of the females from the P-implanted group continued to display regular cycles. By the age of 11 months, 8 of 21 untreated retired breeder females exhibited attenuated LH surges on proestrus and subsequently ceased to display regular estrous cycles within 2 months, whereas the other 13 rats showed normal LH and FSH surges and continued to maintain regular cycles. In contrast to these, aged female rats from the previously mated (15-month-old) and the P-implanted (19-month-old) groups exhibited normal profiles of proestrous LH and FSH surges during regular estrous cycles.(ABSTRACT TRUNCATED AT 400 WORDS)
衰老雌性大鼠正常排卵功能的逐渐停止之前，是正常发情周期中发情前期促黄体生成素（LH）峰的幅度显著下降。然而，我们最近的研究表明，与可育雄性大鼠饲养在一起并经历反复妊娠的衰老雌性大鼠，其LH分泌正常且发情周期规律，这种状态可维持较长时间。由于妊娠大鼠的孕酮（P）分泌持续增加，本研究探讨循环孕酮的反复增加是否能解释这些结果。从8月龄开始至13月龄，经产大鼠分组并进行如下处理：对照组：每笼饲养5只雌性大鼠；交配组：5只雌性大鼠与1只可育雄性大鼠饲养在一起，使其经历反复妊娠；孕酮植入组：每笼饲养5只雌性大鼠，每4周中有3周皮下植入含孕酮的硅橡胶胶囊。在4.5个月的研究期间，孕酮植入组大鼠血清雌二醇（E2）浓度维持在13至27 pg/ml之间，与交配组妊娠雌性大鼠（8 - 26 pg/ml）的水平相似。这些E2值低于发情周期正常的对照组雌性大鼠发情前期血清E2排卵前的升高水平（均值±标准误，56±10 pg/ml）。相比之下，妊娠大鼠和孕酮植入组大鼠的血清P值持续升高，尽管后者（27 - 55 ng/ml）的值约为前一组（117 - 125 ng/ml）的三分之一至二分之一。所有处理在13月龄时停止，此后测定发情周期模式。在13至17月龄期间，交配组正常发情周期大鼠的百分比（13、15和17月龄时分别为50%、36%和15%）显著高于对照组（分别为23%、20%和9%）（P<0.01）。在同一时期，孕酮植入组50%的雌性大鼠继续表现出规律的发情周期。到11月龄时，21只未处理的老龄繁殖雌鼠中有8只在发情前期LH峰减弱，随后在2个月内停止表现出规律发情周期，而其他13只大鼠LH和FSH峰正常，并继续维持规律发情周期。与这些情况形成对比的是，来自先前交配组（15月龄）和孕酮植入组（19月龄）的老龄雌性大鼠在正常发情周期中发情前期LH和FSH峰表现正常。（摘要截断于400字）
