Ultrastructural basis for continued steroidogenesis in the rat polycystic ovary

Because constant light causes persistent estrus in the rat, that animal provides a suitable experimental model for studying the pathogenesis of polycystic ovary disease. We studied the scanning and transmission electron microscopic features of the rat polycystic ovary along with changes in serum estradiol and progesterone concentrations to further elucidate the mechanism of chronic anovulation during persistent estrus. The surface epithelium of the polycystic ovary showed no ovulatory stigmas and contained focal areas of degenerating and proliferating cells. The tunica albuginea was conspicuous, with many fibrils, collagenous materials and fibroblastlike cells adjoining the theca externa layer. The cytoplasm of theca interna cells contained numerous lipid vacuoles and images of extracted cholesterol crystals. The granulosa cells were atrophic and lacked the prominent Golgi apparatus typically found in granulosa cells of proestrous ovaries in cycling rats. With an increasing duration of constant light and chronic anovulation, the mean serum estradiol concentration in persistent-estrus rats was significantly higher and the mean serum progesterone concentration significantly lower than in age-matched controls. Alterations in estradiol-progesterone metabolism in the ovaries may be important etiologic factors in the pathogenesis of chronic anovulation found in polycystic ovary disease in rats.