Abstract
Effects of the uterine cervical stimulation applied at the postpartum estrus was examined in the lactating rats whose pups were removed on various days from 0 to 26 day after parturition. The changes of vaginal smear and the secretion pattern of progestins were followed. In the animals either with (experimental group) or without (control group) the stimulation, the continuation of lactation beyond 24 days after parturition caused the appearance of vaginal estrus. With the shorter lactation periods, however, vaginal estrus appeared only after weaning, and the average date of appearance was about day 3 of post-weaning in the control and day 13 in the experimental group. The length of the post-weaning diestrus in the experimental group coincided with that of pseudopregnancy. The secretion pattern of progestins also strongly suggested that pseudopregnancy had initiated at the time of weaning. If this was the case, the effect of the cervical stimulation would be carried over through the lactation period.
Contrary to the post-weaning secretion patterns of progestins, those of the lactation period were quite similar in both groups. Terefore, the difference of the post-weaning life span of the corpora lutea between the experimental and control groups could not be attributed to the amount of progesterone secreted at the time of weaning. From the results of the daily inspection of the ovaries and tubal ova, it was concluded that the corpora lutea existing during the post-weaning diestrus were formed at postpartum ovulation and an alternation of corpora lutea was not seemed to take place.
