Role of progesterone receptor isoforms in female sexual behavior induced by progestins in rats.

Progesterone and its ring A reduced metabolites regulate female sexual behavior through the direct or indirect activation of progesterone receptor (PR) which has two isoforms with different function and regulation: PR-A and PR-B. The contribution of each PR isoform to the regulation of lordosis in rats is unknown. We explored the role of PR isoforms in lordosis display induced by progesterone and two of its ring A reduced metabolites: 5alpha-pregnan-3,20-dione (5alpha-DHP), and 5beta,3beta-pregnan-20-one (5beta,3beta-Pgl) in adult ovariectomized rats. Two weeks after ovariectomy, the animals were injected subcutaneously with 5 microg of estradiol benzoate (EB), and 40 h later, progestins were injected intracerebroventricularly. PR-B and total PR (PR-A + PR-B) sense or antisense oligonucleotides were administered intracerebroventricularly immediately before EB injection and 24 h later. Lordosis was evaluated 30, 120 and 240 min after progestin administration. Western blot analysis of both PR isoforms was performed in the hypothalamus and preoptic area 24 h after lordosis tests. All progestins induced maximal lordosis 120 min after administration, and antisense oligonucleotides against both PR isoforms inhibited lordosis in all animals. PR-B antisense oligonucleotides also inhibited lordosis induced by progesterone and 5alpha-DHP although with less efficacy than total PR antisense oligonucleotides, but the former inhibited lordosis induced by 5beta,3beta-Pgl in a similar manner as total PR antisense oligonucleotides. In the hypothalamus and preoptic area, the content of both PR isoforms or PR-B alone was diminished by the administration of total or PR-B antisense oligonucleotides, respectively. These results suggest that the PR-B isoform is essential for the display of the lordosis behavior in rats.