Sex differences in the regulation of progesterone receptor isoforms expression in the rat brain.

We studied the effects of estradiol (E2) and progesterone (P) on progesterone receptor (PR) isoforms gene expression in the brain of ovariectomised female and gonadectomised male rats by RT-PCR analysis. In female rats, the expression of both PR isoforms was induced by E2 and down-regulated by P in the hypothalamus, whereas in the preoptic area these changes were only observed in PR-B isoform. On the contrary, in the hippocampus and the olfactory bulb, PR-A was the isoform induced by E2. In these regions, P did not modify the expression of any PR isoform. In the cerebellum and the frontal cortex of female rats, no treatment modified PR isoforms expression. In contrast with female rats, in the male rat brain, PR isoforms expression was only modified in the cerebellum, where PR-A was induced by E2. These results demonstrate a clear sexual dimorphism in the regulation of PR isoforms expression by sex steroid hormones in the rat brain, suggesting that this sex difference contributes to the sexually dimorphic effects of P in the rat brain.