MULTIDRUG-RESISTANCE GENE-EXPRESSION CORRELATES WITH PROGESTERONE PRODUCTION IN DEHYDROEPIANDROSTERONE-INDUCED POLYCYSTIC AND EQUINE CHORIONIC GONADOTROPIN-STIMULATED OVARIES OF PREPUBERTAL RATS

Polycystic ovaries (PCO) can be induced in prepubertal rats by daily i njection of dehydroepiandrosterone (DHEA). There are high levels of pr ogesterone, androgens, and estrogens in the cystic fluid of DHEA-treat ed rat ovaries. The purpose of this study was to investigate whether h igh levels of steroids in the PCO correlate with the expression of mul tidrug resistance gene product P-glycoprotein (Pgp). Using C219, a mon oclonal antibody that recognizes the 170-kDa ATP-dependent transmembra ne pump, we localized Pgp on the plasma membrane of granulosa cells in cystic follicles but not of oocytes or thecal/interstitial cells, in normal prepubertal rats, Pgp was localized in progesterone-producing g ranulosa cells of the preovulatory follicles and in cells of the corpo ra lutea after eCG/hCG stimulation, but not in growing follicles, oocy tes, or thecal/interstitial cells. Northern analysis of these tissues indicated strong expression of Pgp mRNA in the preovulatory follicles, cystic follicles, and corpora lutea. From these findings it seems tha t progesterone produced by the granulosa cells may act in an autocrine manner to induce the expression of Pgp. It may be possible that proge sterone interacts with the Pgp of these granulosa cells to modulate st eroid efflux.