Localization of the progesterone receptor in the porcine ovary

Regulation of progesterone receptor (PR) expression has been studied in many species. However, precise studies have not yet been performed in the porcine ovary. We have examined the localization of PR in follicles and corpora lutea of the porcine ovary at different stages of their development. The effects of LH and FSH on PR expression in granulosa cells of small antral follicles was also studied. Immunohistochemistry was applied to determine the distribution of PR while immunoblot analysis showed that two isoforms A and B were present. Early antral follicles contained PR in the granulosa layer. In granulosa cells of small and medium antral follicles PR was not detected whereas it was present in the theca layer. Before ovulation, PR was found in both granulosa and theca cells of large follicles and the staining intensity was very strong. FSH or LH treatment of small follicles (100 ng/ml) induced changes in cellular distribution patterns of PR. In both cases, PR was expressed in granulosa cells. PR was detected in corpora lutea in all 3 stages of the luteal phase. Our data show that in the pig ovary changes in PR localization are stage-specific and suggest that expression of PR is positively regulated by both LH and FSH.