Matt D W, Sarver P L, Lu J K
Department of Obstetrics/Gynecology, UCLA School of Medicine 90024.
Biol Reprod. 1987 Sep;37(2):421-30. doi: 10.1095/biolreprod37.2.421.
In the female rat, the incidence of regular estrous cyclicity and fertility decreases progressively during aging, and the causes for these are unknown. To reveal the biology of pregnancy in aging rats, we performed a longitudinal study in a colony of multiparous rats bred every 2 mo. Beginning at 4 mo and continuing to 12 mo of age in these same individual females, we determined the chronological changes in estrous cyclicity, examined the relationship between the estrous cycle pattern and fertility, and recorded the numbers of live and dead pups delivered at term. In separate groups of 4- to 12-mo-old multiparous rats, we counted the number of ova present in the oviducts (ovulation rate) one day after mating and the number of grossly normal blastocysts found in the uteri on Day 5 of pregnancy. Similar studies were also performed in primiparous rats of 8, 10, and 12 mo of age. The cessation of regular cyclicity during aging occurred significantly (p less than 0.01) earlier in virgin than multiparous rats. Fertility followed a similar but more dramatic pattern of decline than did the incidence of regular cyclicity in both the multiparous and virgin females. Few irregularly cyclic and persistent-estrous females had fertile gestations after mating, and increasing proportions of regularly cyclic females also failed to reproduce successfully at middle age (8-12 mo). Thus, regular ovulatory cycles were essential but not sufficient for fertile gestations in aging rats. Beginning at 6 mo of age, the litter sizes of multiparous rats decreased progressively, and these decreases were associated with a similar decline in the number of live but not dead pups delivered. Also, the percentage of dead pups/total number of pups delivered increased steadily during aging in multiparous (from 14% to 69%) but not primiparous females. The litter sizes of 8- to 10-mo-old primiparous females were not different from those of multiparous rats. However, the litter sizes of irregularly cyclic rats were consistently smaller than those of regularly cyclic females. Thus, parity had little effect on fecundity in aging females, whereas the cessation of regular ovulatory cycles during aging greatly decreased both the incidence of fertility and the litter size.(ABSTRACT TRUNCATED AT 400 WORDS)
在雌性大鼠中，随着年龄增长，规律的发情周期和生育能力的发生率逐渐降低，而其原因尚不清楚。为了揭示老龄大鼠怀孕的生物学特性，我们在每2个月繁殖一次的经产大鼠群体中进行了一项纵向研究。从4个月开始，在这些相同的个体雌性大鼠中持续到12个月龄，我们确定了发情周期的时间变化，研究了发情周期模式与生育能力之间的关系，并记录了足月分娩的活仔和死仔数量。在4至12月龄经产大鼠的不同组中，我们在交配后一天计算输卵管中卵子的数量（排卵率）以及在怀孕第5天子宫中发现的大体正常囊胚的数量。在8、10和12月龄的初产大鼠中也进行了类似的研究。在老龄期，规律周期的停止在未孕大鼠中比经产大鼠显著更早出现（p小于0.01）。在经产和未孕雌性大鼠中，生育能力遵循与规律周期发生率相似但更显著的下降模式。很少有发情周期不规律和持续发情的雌性大鼠在交配后有可育的妊娠，并且在中年（8至12个月）时，规律发情周期的雌性大鼠中也有越来越大比例未能成功繁殖。因此，规律的排卵周期对于老龄大鼠的可育妊娠至关重要，但并不充分。从6个月龄开始，经产大鼠的窝仔数逐渐减少，这些减少与活仔数量的类似下降有关，但与死仔数量无关。此外，在经产雌性大鼠中，死仔占分娩仔鼠总数的百分比在老龄期稳步增加（从14%增至69%），但在初产雌性大鼠中并非如此。8至10月龄初产雌性大鼠的窝仔数与经产大鼠无异。然而，发情周期不规律的大鼠的窝仔数始终小于发情周期规律的雌性大鼠。因此，胎次对老龄雌性大鼠的繁殖力影响不大，而老龄期规律排卵周期的停止极大地降低了生育能力的发生率和窝仔数。（摘要截短至400字）
