PRESENCE OF BETA-MERCAPTOETHANOL CAN INCREASE THE GLUTATHIONE CONTENTOF PIG OOCYTES MATURED IN-VITRO AND THE RATE OF BLASTOCYST DEVELOPMENT AFTER IN-VITRO FERTILIZATION

The present study examined the effect of beta-mercaptoethanol (BME) du ring in vitro maturation (IVM) of pig oocytes on in vitro fertilizatio n (IVF) parameters, intracellular glutathione (GSH) concentration, sub sequent embryo development and blastocyst cell numbers. Cumulus-oocyte complexes were cultured in North Carolina State University (NCSU)-23 medium containing porcine follicular fluid, cysteine, hormonal supplem ents and 0 to 50 mu M BME for 20 to 22 h. They were then cultured in t he same medium but without hormonal supplements for an additional 20 t o 22 h. After culture, cumulus-free oocytes were coincubated with froz en-thawed spermatozoa for 5 to 6 h. Putative embryos were transferred to NCSU-23 containing 0.4% BSA and cultured for 144 h (Experiment 1). In comparisons between the presence or absence of BME, no differences were observed in fertilization parameters. At 48 h, no mean difference s were found in cleavage rates. However, at 144 h, compared with no ad dition (26%), the presence of 12.5 and 25 mu M BME increased (P<0.05) the proportion of blastocysts in a dose-dependent manner (34 and 41%). Further increase from 25 to 50 mu M BME reduced (P<0.05) the blastocy st development rate. Blastocysts derived from oocytes matured with 25 mu M BME had the highest (P<0.05) trophectoderm (TE) and total cell nu mbers. No difference was found in inner cell mass (ICM) cells among tr eatments. In Experiment 2, after IVM,oocytes were fixed to analyze the GSH concentration. Compared to no addition, a higher (P<0.01) level o f GSH was found in oocytes matured with 25 mu M BME. Compared with 25 mu M BME, GSH was low (P<0.05) at 50 mu M BME. The results show that a t certain concentrations BME in IVM medium has beneficial effects on s ubsequent embryo development, and is correlated with intracellular GSH level in pig oocytes. (C) 1998 by Elsevier Science Inc.