EFFECTS OF OVIDUCTAL FLUID ON SPERM PENETRATION AND CORTICAL GRANULE EXOCYTOSIS DURING FERTILIZATION OF PIG OOCYTES IN-VITRO

The effects of oviductal fluid on sperm penetration and cortical granu le exocytosis in pigs were examined. Cortical granule exocytosis in oo cytes matured in vivo and in vitro was observed by staining with fluor escent-labelled lectin and laser-scanning confocal microscopy. Exocyto sis of matured oocytes was classified into three categories after in v itro fertilization: complete cortical granule exocytosis and even dist ribution of exudate in the entire perivitelline space (type I); comple te exocytosis and partial distribution of exudate (type II) and incomp lete cortical granule exocytosis (type III). The incidence of oocytes with type I exocytosis was higher in oocytes matured in vivo than in t hose matured in vitro. The addition of oviductal fluid at a concentrat ion of 1% or 10% to the fertilization medium decreased sperm penetrati on and the mean number of spermatozoa present in penetrated eggs. The distribution of cortical granule exudate was not different in the pres ence of 1% oviductal fluid after sperm penetration from that of contro l groups. When oocytes were cultured for 1.5 h in medium containing 10 % or 30% oviductal fluid before insemination, the incidence of monospe rmy increased without a decrease in sperm penetration. Preculture of o ocytes in medium containing 30% oviductal fluid increased type I corti cal granule reaction and increased resistance of the zona pellucida to dissolution by 0.1% (w/v) pronase at the time of sperm penetration. T hese results suggest that a factor(s) from the oviductal secretion is required for the complete cortical granule reaction and in the modific ation of the zona pellucida.