[Morphological and biochemical events in the periovulatory period in ovarian follicles of rats. In vitro studies].

Cultures of rat ovarian follicles obtained at the proestrus were investigated during 24 hours following a supply of gonadotropins (FSH, LH, Prolactin) used in order to stimulate their physiological rise at the proestrus. As showed by the cytological study, the initiating luteinization appeared in follicles after 24 hours. Progesterone, testosterone and oestradiol-17 beta were assayed in culture media. The three gonadotropins induced a significant fall of the oestradiol-progesterone ratio whereas testosterone levels were unmodified; at first they increased and then inhibited the oestradiol-17 beta synthesis. On the other hand, progesterone rose one hour after oestradiol-17 beta but its secretion persisted. Thus, the inhibition of the enzymatic aromatization of steroids on one hand, the evidence of a new metabolic way leading to the increasing synthesis of progesterone on the other hand would be due to the preovulatory rise of gonadotropins. After exposition for 4 hours to FSH, LH and Prolactin, a new supply of LH did not modify testosterone and oestradiol-17 beta levels but led to a significant increase in the secretion of progesterone. so mechanisms induced by the proestrus preovulatory peak would seem irreversible.