INHIBITORY-ACTION OF HYPOXANTHINE ON MEIOTIC RESUMPTION OF DENUDED PIG FOLLICULAR OOCYTES IN-VITRO

The present study was conducted to investigate the direct action of hy poxanthine, which has been reported to be present in pig follicular fl uid, on spontaneous meiotic resumption of pig denuded oocytes in vitro . No oocytes, which were surrounded by a cumulus and some membrana gra nulosa cells directly adjacent to it from healthy antral follicles, un derwent germinal vesicle breakdown (GVBD) when they were cultured in s erum-supplemented 199 with or without 4 mM hypoxanthine. On the other hand, 81% of denuded oocytes prepared from such cumulus-oocyte-granulo sa cell complexes showed GVBD after 24 h of culture. Hypoxanthine inhi bited significantly this spontaneous resumption of meiosis in denuded oocytes. The inhibitory action of hypoxanthine was dose dependent at c oncentrations of 1-6 mM and was reversible following subsequent cultur e of the oocytes in hypoxanthine-free medium. However, premature chrom osome condensation was observed in oocytes cultured in hypoxanthine-su pplemented medium, and the oocytes released from the influence of hypo xanthine completed GVBD and reached the second metaphase slightly fast er than those freshly isolated from the follicle. These results sugges t that hypoxanthine inhibits spontaneous meiotic resumption of pig ooc ytes in vitro. However, the inhibitory action of hypoxanthine does not prevent all events involved in GVBD from occurring. (C) 1995 Wiley-Li ss, Inc.