Influence of bovine follicular and oviduct fluids on sperm capacitation in vitro.

The ability of bovine follicular fluid (FF) and oviduct fluid (ODF) to capacitate sperm was determined. At concentrations of greater than 20%, both FF and ODF capacitated sperm within 4 hours, but at concentrations greater than 40%, FF also initiated the acrosome reaction. Non-luteal ODF at a concentration greater than 60% capacitated sperm within 2 hours. Non-luteal ODF maintained sperm motility better than either luteal ODF or FF. Sperm previously capacitated in ODF underwent the acrosome reaction when exposed to solubilized zonae pellucidae (25 ng/microL) or FF (20%, V/V). Sperm treated with 60% non-luteal ODF or 60% FF fertilized more oocytes at 2 hours than did sperm in treatments with less concentrated fluid. After 4 hours, all fluid treatments and modified Tyrode's medium supplemented with heparin exhibited a higher percentage of fertilized oocytes than the modified Tyrode's medium alone. Concentrations of both protein and glycosaminoglycans were significantly lower in ODF than in either blood serum or FF. These studies demonstrated that ODF capacitated sperm and sustained motility, but sperm were capacitated more rapidly in non-luteal than in luteal ODF. In contrast, FF was able to both capacitate sperm and induce the acrosome reaction. These effects of ODF and FF on aspects of sperm function were uniquely concentration-dependent, suggesting that different mechanisms may operate in ODF and FF to regulate these events.