Enhancement of bovine oocyte fertilization in vitro with a bovine oviductal specific glycoprotein.

The purpose of this study was to determine the effect of a partially purified bovine oviductal glycoprotein (bOGP) on fertilization rates of bovine oocytes. The effect of albumin (control protein) or bOGP at 100 micrograms ml-1 during the 16-18 h fertilization period was evaluated in a standard IVF system using a sperm concentration between 0.5 and 0.125 x 10(6) spermatozoa ml-1. bOGP maintained a higher (P < 0.05) fertilization rate (62.0% versus 31.2%) at 0.125 x 10(6) spermatozoa ml-1 compared with the albumin control. The enhancement of fertilization by bOGP was blocked by the inclusion of a specific antibody to bOGP, whereas the antibody with albumin had no effect. A 2 h gamete preincubation step was subsequently included in the IVF procedure (0.125 x 10(6) spermatozoa ml-1) to determine whether the effect of bOGP was mediated through an interaction with the oocyte, the spermatozoon or both. When oocytes were preincubated with bOGP the fertilization rates were higher (P < 0.05) than with the albumin control (oocytes and spermatozoa exposed to albumin), whereas preincubation of spermatozoa with bOGP did not affect fertilization rates. There was no synergistic effect of preincubating oocytes and spermatozoa with bOGP. The increase in fertilization rate achieved by preincubating oocytes with bOGP was blocked with a specific antibody to bOGP. These results suggest that the increase in fertilization rates observed when bOGP is included during the 16-18 h fertilization period are primarily mediated through the interaction of bOGP with the oocyte since the same facilitatory effect was observed with a 2 h preincubation of oocytes before IVF. The ability to block these effects with a polyclonal antibody specifically generated against bOGP shows that this biological activity is due to bOGP. In summary, bOGP enhances fertilization in bovine oocytes whether it is included during preincubation or insemination and this appears to be due to a direct effect on the oocyte.