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 μg ml-2) 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. Under paraffin oil, the concentration further decreased during equilibration (to 128.0 ± 13.3 ng ml-1) during the first 20 h of culture (42.8 ± 19.4 ng ml-1) and also during the second 20 h period of culture without hormonal supplements (0.925 ± 0.544 ng ml-1). The concentrations of progesterone in maturation media under paraffin oil were lower throughout maturation (1.0 ± 0.2 ng ml-1 at 0 h to 6.9 ± 1.5 ng ml-1 after 40 h). These results demonstrate that at least two different hormonal conditions during maturation, which are the presence of PMSG during the first 20 h of culture and the absence of PMSG and oestradiol during the second 20 h of culture, are beneficial to meiotic and cytoplasmic maturation of pig oocytes. Furthermore, it was demonstrated that oocyte-cumulus complexes under paraffin oil were exposed to extremely low concentrations of steroids during maturation.
|Number of pages||7|
|Journal||Journal of Reproduction and Fertility|
|Publication status||Published - 1994|
ASJC Scopus subject areas
- Molecular Biology
- Obstetrics and Gynaecology
- Developmental Biology