Effect of oviduct cells on the incidence of polyspermy in pig eggs fertilized in vitro

The consequences of interactions between porcine sperm, eggs, and oviduct cells before and during fertilization in vitro (IVF) has been examined with particular reference to the block to polyspermy. The pattern of polypeptides secreted by porcine oviduct epithelial cells has been determined and its effects on sperm both during pre-fertilization co-culture and during fertilization have been examined. In standard IVF procedures with no oviduct cell involvement, high rates of penetration (91%) were accompanied by equally high rates of multiple sperm penetration (91% of penetrated eggs). Fertilization on oviduct cell monolayers or a combination of 1 h co-culture of sperm and oviduct cells before the addition of in vitro matured oocytes did not reduce polyspermy. However, a sperm-oviduct cell co-culture period of 2.5 h followed by IVF on oviduct cells selectively reduced the rate of polyspermy by 40% and 50% in two separate series of trials (United Kingdom and Japan, respectively): Overall fertilization rates after this treatment were high (95% or 84%, respectively). A 3.5 h period of pre-fertilization co-culture further reduced polyspermy to only 14% of penetrated eggs, but this treatment was accompanied by a sharp drop in the fertilization rate from an overall mean of 88% for all other groups to 19% after 3.5 h co-culture.