Effect of bovine oviductal estrus-associated protein on the ability of sperm to capacitate and fertilize oocytes.

At estrus, an oviduct-specific, estrus-associated glycoprotein (EAP) of molecular weight 85-95,000, is secreted by the oviductal epithelium and found in cannula-derived bovine oviductal fluid (ODF). The objectives of these studies were to determine if bovine sperm were capacitated by EAP in vitro, whether this effect differed for EAP derived from ODF versus conditioned medium from oviduct ampullar explants, and to determine if sperm capacitated in vitro with EAP-fertilized bovine eggs. Sperm were incubated for up to 6 hours with partially purified EAP derived from ODF and assessed for capacitation by their ability to undergo the acrosome reaction following exposure to lysophosphatidylcholine. At 4 hours of incubation, the number of capacitated sperm in treatments containing 50% ODF or EAP plus bovine serum albumin (BSA) was similar, and it was significantly greater than the number of capacitated sperm in treatments containing antibodies to EAP. Using purified EAP derived from ampullar explant-conditioned medium, twice the number of sperm were capacitated after 4 hours with EAP from conditioned medium or with ODF than with treatments containing anti-EAP. The fertilizing ability of sperm incubated with EAP was significantly greater than that for sperm incubated without EAP or with anti-EAP. We conclude that bovine EAP, derived from both ODF and in vitro cultures, promotes sperm fertilizing ability.