INVITRO STUDIES OF OOCYTE MATURATION AND FOLLICULAR METABOLISM IN THE PIG

In the in vivo developing follicles estrogen level raises proportionally to the size of the follicle. Progesterone concentration parallel this curve at lower concentrations ; a significant level of progesterone is, however, always noted. A switch of E2/Pg ratio from 2.0 (or higher) to 0.15 occurs after the onset of estrus, when meiosis resumes. In vitro the E2/Pg ratio changes only to follicles of 7.0 mm or larger in diameter when either oFSH or oLH is added to the culture medium; meiosis always resumes and the ganulosa and cumulus cell reactions are similar to those occurring in vivo. During culture of follicles < 6 mm the reduction of the E2/Pg ratio is not observed whatever the nuclear status may be at the end of culture. For the nuclear maturation of oocytes high progesterone concentration thus does not seem to be necessary. No consistent morphological changes of the granulosa and cumulus cells could be associated with meiotic maturation of the oocyte. Glucose consumption increases when gonadotropins are added to the medium by maximal increase is only observed when meiosis resumes.