Vom Saal F S, Moyer C L
Biol Reprod. 1985 Jun;32(5):1116-26. doi: 10.1095/biolreprod32.5.1116.
The production of live young during successive pregnancies was investigated in female CF-1 house mice (Mus musculus) identified at cesarean delivery as having developed in utero between 2 male fetuses (2M females) or not next to a male fetus (0M females). 2M female mice have previously been found to be exposed to higher concentrations of testosterone than 0M females during fetal life, presumably as a result of the transport of steroids between contiguous fetuses. 0M and 2M females were paired with stud males. The males were removed prior to delivery of a litter and replaced by other males when the litter was weaned. This process was repeated until: 1) a female did not become pregnant within 2.5 mo or 2) two successive litters were produced in which all of the pups were dead. In Experiment 1 females were first mated when 25 days old, and 2M females ceased producing litters containing live pups at a younger age and after fewer litters than did 0M females; however, many females were terminated from the study as a result of producing 2 successive litters of dead young rather than failing to become pregnant during a 2.5-mo period. There was a gradual decline in the number of live young produced by 0M females as a function of age and parity, but 2M females abruptly ceased producing any live young after producing a litter of normal size. For the last live litter, there were thus significantly fewer live young produced by 0M females than by 2M females. None of these differences were observed in Experiment 2, in which 0M and 2M females were mated for the first time beginning at 7 mo of age. The 2M females in this experiment ceased producing live young at a significantly older age than did the 2M females first mated at puberty. In contrast, there was no effect of age at initial mating on the age at which 0M females ceased producing live young. This finding suggests that exposure of 2M females to elevated titers of testosterone during fetal life results in a reduction in reproductive life span if they first become pregnant during the pubertal period.
在剖宫产时被确定为在子宫内发育于两个雄性胎儿之间（2M雌性）或不在雄性胎儿旁边（0M雌性）的CF - 1雌性家鼠（小家鼠）中，研究了连续妊娠期间活仔的产生情况。先前发现，2M雌性小鼠在胎儿期接触的睾酮浓度高于0M雌性小鼠，这可能是由于相邻胎儿之间类固醇的转运所致。将0M和2M雌性小鼠与种公鼠配对。在产仔前将雄性移除，并在幼仔断奶时用其他雄性替换。重复这个过程，直到：1）雌性在2.5个月内未怀孕，或2）产下两窝连续的幼仔且所有幼仔均死亡。在实验1中，雌性在25日龄时首次交配，与0M雌性相比，2M雌性在更年轻的年龄且产仔数更少时就停止产生包含活仔的窝；然而，许多雌性因产下两窝连续的死仔而非在2.5个月期间未能怀孕而被终止研究。0M雌性产生的活仔数量随着年龄和产次逐渐下降，但2M雌性在产下一窝正常大小的幼仔后突然停止产生任何活仔。因此，对于最后一窝活仔，0M雌性产生的活仔明显少于2M雌性。在实验2中未观察到这些差异，在该实验中，0M和2M雌性从7月龄开始首次交配。该实验中的2M雌性停止产生活仔的年龄明显大于青春期首次交配的2M雌性。相比之下，首次交配时的年龄对0M雌性停止产生活仔的年龄没有影响。这一发现表明，如果2M雌性在青春期首次怀孕，胎儿期暴露于高滴度的睾酮会导致生殖寿命缩短。
