Relationship between steroidogenesis and oocyte maturation in rat graafian follicles cultured in vitro

Rat Graafian follicles were dissected from ovaries during the morning of proestrus and incubated in various media. After an 8 h incubation period, ovarian follicles were collected and analyzed, by radioimmunoassay, for progesterone, 17 alpha-hydroxyprogesterone, androstenedione, estradiol-17 beta, and dihydrotestosterone. Following incubation in proestrus (a.m.) serum, preovulatory follicles secreted all these steroids and the output of progesterone, 17 alpha-hydroxyprogesterone and androstenedione was markedly stimulated following the addition of LH to the media. Follicle-enclosed oocytes resumed meiosis when incubated in proestrus serum without added LH. However, germinal vesicle break-down (GVBD) under these conditions was considerably slower than that observed following addition of LH to the medium. "Spontaneous" maturation of oocytes in proestrus serum was associated with increased production of steroids. Oocyte maturation and steroidogenesis both occurred following incubation of ovarian follicles in serum obtained from hypophysectomized rats. Addition of LH to the media markedly accelerated these responses. These results suggest that oocyte maturation and steroidogenesis also occur in cultured ovarian follicles in the absence of gonadotrophic hormones. The relationship between steroidogenesis and/or spontaneous oocyte maturation are discussed.