Hormonal regulation of ovarian function in vivo and in vitro

In the ovary steroids are produced by the follicles, corpora lutea and interstitial cells. In the follicle a substantial steroid production starts after the antrum formation and the main steroid produced is estradiol which supports folliculogenesis. Its content rises as the follicle grows. In the preovulatory period of time estradiol, released in a great amount into the circulation, triggers the ovulation inducing discharge of LH from the pituitary gland. Afterwards the follicle stops producing estradiol and androgens and starts to form progesterone. Such a swish in steroid synthesis is a universal feature for many species investigated. The results of experiments suggest that this swish is due to the inhibition of androgen production and a subsequent decline of aromatase activity. After ovulation progesterone synthesis is continued by corpus luteum (CL). The pattern of steroids produced by CL depends upon the stage of luteal phase and upon the species investigated. In the pig newly formed CL contain little steroids. The highest progesterone and androgen content is characteristic for mature and midway CL. In regressing CL progesterone and androgen concentrations drop while estradiol reaches its highest level. Steroid synthesis is modulated by gonadotropins and steroids.