IS CAMP DECREASE ESSENTIAL FOR RESUMPTION OF MEIOSIS IN MOUSE OOCYTES

Resumption of meiosis was inhibited in mouse oocyte cumulus complexes (OCC) co-cultured with pig membrana granulosa (PMG). After 3 and 6 h o f co-culture these oocytes possessed an intact nuclear envelope and th eir nucleolar surface was associated with granules approximate to 80 n m in diameter. Preincubation of OCCs for 30, 45, 60 or 90 min followed by co-culture with PMG for 2 h of either OCCs or denuded oocytes resu lted in germinal vesicle breakdown (GVBD) in approximate to 0, 30, 70 and 100% mouse OCCs and in approximate to 30, 60, 80 and 100% denuded oocytes, respectively. It seems that the inhibitory contact between mo use oocytes and PMG was established during the first h of co-culture. After isolation from antral follicles the oocytes contained 2.75 fmol cyclic adenosine 3', 5'-monophosphate (cAMP). When OCCs were co-cultur ed for 1, 2 or 3 h with PMG, the amount of cAMP per oocyte was 1.34, 1 .33 and 1.51 fmol, respectively. After culture of OCCs in control medi um the amount of cAMP was 1.21, 1.39 and 2.16 fmol, respectively. The present results suggest that the inhibitory activity of PMG is not spe cies-specific. Moreover, PMG prevented resumption of meiosis in mouse oocytes in spite of the cAMP drop in oocyte cytoplasm characteristic o f the resumption of meiosis.