287 EFFECT OF CYSTEAMINE DURING IN VITRO MATURATION OF OPU DERIVED BOVINE OOCYTES ON FURTHER IN VITRO EMBRYONIC DEVELOPMENT AND PREGNANCY RATE

Abstract

Glutathione (GSH) plays an important protective role in relation to reactive oxygen species generated by normal oxidative metabolism in the cell. The presence of cysteamine during in vitro maturation may facilitate the synthesis of GSH by immature oocytes. In a previous study we showed a positive effect of the presence of cysteamine during in vitro maturation of slaughterhouse derived bovine oocytes on subsequent in vitro embryonic development (Merton et al. 2004 Rep. Fert. Dev. 16, 279 abstract). This report shows the results of a field trial with ultrasound guided transvaginal oocyte collection (OPU) derived oocytes, in order to confirm our previous results obtained with slaughterhouse derived oocytes. Immature cumulus–oocyte complexes (COCs) were recovered twice weekly by ovum pick-up (OPU) at two collection centres from 11 cows and 147 pregnant heifers. COCs were matured in vitro in TCM199/FCS/LH/FSH supplemented either with or without cysteamine (0.1 mM). Subsequently, matured oocytes were fertilised with frozen-thawed gradient-separated semen and further cultured for 7 days in SOFaaBSA. At Day 7, Morula grade 1 (IETS) were transferred fresh and early-, mid- and exp-Blast grade 1 and 2 were transferred either fresh or frozen/thawed. The experimental design was a 2 × 2 factorial. Results were analysed by Chi-square analyses. The results show that the presence of cysteamine during in vitro maturation significantly affected embryo production from OPU derived COCs (23.4% and 34.4% Morula + Blastocyst rate at Day 7 for control and cysteamine, respectively; Table 1). This higher embryo production rate was mainly due to an increased number of Blastocysts. Also the proportion of grade 3 embryos was significantly reduced in the cysteamine group (P < 0.01). The number of transferable embryos per session was 1.06 and 1.73 for control and cysteamine, respectively. Pregnancy rate was not significantly affected by the presence of cysteamine during in vitro maturation for both fresh and frozen/thawed embryos (fresh: 40.5% and 44.8%, frozen/thawed: 44.4% and 47.2% for control and cysteamine, respectively). These results show that the presence of cysteamine during in vitro maturation affects further in vitro embryonic development, resulting in a higher embryo production rate. This suggest that an apparently ‘simple’ extra protection of the oocyte, due to the free radical scavenging potency of GSH, can have an enormous effect (63.2% relative increase in transferable embryos) on its in vitro developmental potency. The intrinsic quality of the ‘extra’ produced transferable embryos seems not to be different, since pregnancy rate was not affected.

Table 1. Effect of cysteamine during in vitro maturation of OPU-derived bovine oocytes on subsequent in vitro embryonic development