GLUTATHIONE CONCENTRATION DURING MATURATION AND AFTER FERTILIZATION IN PIG OOCYTES - RELEVANCE TO THE ABILITY OF OOCYTES TO FORM MALE PRONUCLEUS

The present study examined the kinetics of glutathione (GSH) concentra tion during maturation and after fertilization in pig oocytes and its relevance to the ability of pig oocytes to form a male pronucleus afte r in vitro fertilization. The GSH concentration was significantly high er in pig oocytes matured in Waymouth medium than in pig oocytes matur ed in either modified (m) TCM-199 or mTLP media. The addition of 0.04- 0.57 mM cysteine (CySH) to mTLP significantly increased both the GSH c oncentrations in oocytes matured in vitro and the rate of male pronucl eus formation as compared to those in oocytes cultured in mTLP alone. When pig oocytes were cultured 12, 24, or 36 h in mTLP plus 0.14 mM Cy SH, their GSH concentrations were significantly higher than in uncultu red oocytes. After fertilization, the GSH concentration in pig oocytes declined significantly. GSH concentrations in oocytes matured in vivo did not differ from those in oocytes matured in mTLP plus 0.14 or 0.5 7 mM CySH. The results indicate that 1) the composition of maturation medium affects the GSH concentration in pig oocytes; 2) the addition o f CySH to maturation medium permits GSH synthesis by the pig oocytes; 3) GSH levels in pig oocytes change during maturation and after fertil ization; and 4) GSH synthesis during oocyte maturation is an important factor for promoting their ability to form a male pronucleus after fe rtilization.