Role of progesterone receptors during postpartum estrus in rats

We studied the role of progesterone receptor (PR) in the display of female sexual behavior during postpartum estrus in rats. Adult female rats were treated with the PR antagonist, RU486 (1.25 and 5mg), 3h after parturition and sexual behavior was evaluated throughout the first postpartum day. Estradiol and progesterone serum levels changed during the first 24h postpartum. The highest estradiol and progesterone levels were found at 9 and 12h postpartum, respectively. The predominant PR isoform in the hypothalamus and the preoptic area was PR-A during postpartum day. The content of PR-A increased at 6h postpartum in the hypothalamus and the preoptic area, and decreased in both regions at 9h. PR-B content only increased in the preoptic area at 12h postpartum. The highest display of lordotic and proceptive behaviors were found at 12h postpartum. The treatment with 1.25 and 5mg of RU486 respectively reduced lordosis by 61% and 92% at 12h postpartum. These results suggest that PR is essential in the display of postpartum estrus in rats. ►Intracellular progesterone receptors (PR) are essential in the display of postpartum estrus in rats. ►Serum estradiol and progesterone levels change throughout the first postpartum day. ►PR-A isoform is predominant in hypothalamus and preoptic area during postpartum. ►PR-B isoform expression increases at 9 and 12h postpartum when there is a high display of sexual behavior.