Sherwood O D, Downing S J, Rieber A J, Fraley S W, Bohrer R E, Richardson B C, Shanks R D
Endocrinology. 1985 Jun;116(6):2554-62. doi: 10.1210/endo-116-6-2554.
In the rat, the antepartum elevation of serum relaxin levels consists of two phases separated by a 24-h interval. The second phase, which occurs between 36 and 24 h before birth, is temporally closely associated with functional luteolysis. Relaxin levels then decline throughout the last approximately 24 h of pregnancy. We have postulated that the two phases in the antepartum elevation of serum relaxin levels may be indicative of an increasingly effective endogenous circadian luteolytic process. There is limited evidence that both luteolysis and birth are delayed in rats with small litters. The present study investigated in detail the relationship between litter size and the timing of both functional luteolysis and birth in rats. The number of conceptuses (C) in Sprague-Dawley-derived rats was surgically adjusted on day 8 of pregnancy (day 8) so that rats bore one, two, three, five, or a full complement (FC) of eight or more C. Rats were maintained under a photoperiod regimen of 14 h of light and 10 h of darkness (lights on from 2100-1100 h) beginning on day 8 and observed for birth at 10-min intervals from 2100 h on day 22. Serum levels of both relaxin and progesterone were determined in blood samples obtained at 4-h intervals from 2400 h on day 19 until birth. Ninety-five percent of the rats that had five or more C gave birth during the light phase on day 23, which was designated the normal birth interval. However, only 20% of the rats with three C or less, gave birth during the normal birth interval, and 47% gave birth about 24 h later during the light phase on day 24, which was designated the late birth interval. The 24-h delay in birth of rats with small litters which delivered during the late birth interval appears to be attributable to a delay in functional luteolysis; the antepartum decline in serum relaxin and progesterone levels occurred about 24 h later in these rats than in rats that delivered during the normal birth interval. It is concluded that the C may be associated with the luteolytic process and thereby influence the time of birth in rats. Additionally, the results of this study are consistent with our hypothesis that there is an endogenous circadian luteolytic process in rats during the antepartum period.
在大鼠中，产前血清松弛素水平的升高分为两个阶段，中间间隔24小时。第二阶段发生在出生前36至24小时之间，在时间上与功能性黄体溶解密切相关。然后，在妊娠的最后约24小时内，松弛素水平下降。我们推测，产前血清松弛素水平升高的两个阶段可能表明内源性昼夜节律性黄体溶解过程越来越有效。有有限的证据表明，产仔数少的大鼠黄体溶解和出生都会延迟。本研究详细调查了大鼠产仔数与功能性黄体溶解时间和出生时间之间的关系。在妊娠第8天（第8天）通过手术调整斯普拉格-道利品系大鼠的孕体数量（C），使大鼠产下一、二、三、五个或八个或更多C的完整数量（FC）。从第8天开始，将大鼠置于14小时光照和10小时黑暗的光周期方案下（21:00-11:00开灯），并从第22天21:00开始每隔10分钟观察一次出生情况。从第19天24:00到出生，每隔4小时采集一次血样，测定血清中松弛素和孕酮的水平。有五个或更多C的大鼠中，95%在第23天的光照阶段分娩，这被指定为正常出生间隔。然而，只有20%产仔数为三个或更少的大鼠在正常出生间隔内分娩，47%在第24天的光照阶段约24小时后分娩，这被指定为晚出生间隔。在晚出生间隔内分娩的产仔数少的大鼠出生延迟24小时，这似乎归因于功能性黄体溶解的延迟；这些大鼠血清松弛素和孕酮水平的产前下降比在正常出生间隔内分娩的大鼠晚约24小时。结论是，孕体数量可能与黄体溶解过程有关，从而影响大鼠的出生时间。此外，本研究结果与我们的假设一致，即在产前期间大鼠存在内源性昼夜节律性黄体溶解过程。
