Inhibition of nuclear maturation of isolated rat oocytes by follicular constituents

In vitro studies of mammalian oocytes led to the suggestion that a follicular factor, derived from granulosa cells (GC) and accumulated in follicular fluid (FFI), prevents the resumption of meiosis within the large Graafian follicle(s). The objectives of the present study were to test the effect upon the maturation of rat oocytes of (a) porcine FFI and a low molecular weight fraction thereof (PFFI), and (b) coculture with rat GC. Both FFI and PFFI inhibited the resumption of meiosis (germinal vesicle brakdown, GVB) of rat oocytes cultured with adherent cumulus cells. Coculture of oocytes with freshly isolated rat GC did not affect the spontaneous resumption of maturation, but GC cultured for 24 hrs before adding the oocytes inhibited maturation. Culture of oocytes in a medium in which GC had been cultured for 48 hrs resulted in similar inhibition of meiosis. Addition of LH (5 yg/ml) overcame the inhibitory action of coculture with GC but only partially reversed the effect of GC conditioned medium and of PFFI. These studies demonatrate that (1) the maturation inhibiting action of porcine FFI is not confined to oocytes of that species ;