Different hormonal requirements of pig oocyte–cumulus complexes during maturation <i>in vitro</i>

Abstract

Cytoplasmic maturation as determined by male pronuclear formation following fertilization in vitro was examined in pig oocytes cultured under different hormonal conditions during either the first or second 20 h period of in vitro maturation. Exposure to several combinations of pregnant mares' serum gonadotrophin (PMSG) (10 IU ml-1), hCG (10 IU ml-1) and oestradiol (1 microgram ml-1) for a second 20 h period following culture in a medium supplemented with these hormones for 20 h did not result in differences among treatment groups in maturation rates, penetration rates or polyspermy rates. However, supplementation with PMSG and oestradiol for the last 20 h of culture reduced male pronuclear formation rates significantly. When oocyte-cumulus complexes were cultured in hormone-free media for 20 h after culture in several combinations of supplemental hormones for the first 20 h period, germinal vesicle breakdown rates and maturation rates were lower in oocytes previously exposed to oestradiol alone or no hormonal supplements (68-70% and 45-49%, respectively) than in oocytes previously exposed to PMSG or hCG (89-99% and 71-89%, respectively). Exposure of oocytes to oestradiol alone also reduced the penetration rate (61%) compared with PMSG or hCG (86-99%). Supplementation of media with PMSG alone or together with other hormones increased the male pronuclear formation rate (63-72%) compared with supplementation with oestradiol (33%) or no hormonal supplements (32%). The concentration of oestradiol in maturation medium decreased at filtration (to 216.5 +/- 72.6 ng ml-1) before culture.(ABSTRACT TRUNCATED AT 250 WORDS)