Electrophoretic characterization of equine oviductal fluid.

To characterize further the events involved in fertilization and early embryonic development in the mare, effect of the estrous cycle on oviductal fluid proteins was investigated. Five mares had indwelling cannulas placed in their oviducts so that fluid could be collected throughout the estrous cycle. Daily fluid volumes were recorded and mares were monitored for signs of standing estrus. Oviductal fluid samples were pooled across mares according to stage of cycle (either estrus or nonestrus) for further analysis. Two-dimensional polyacrylamide gel electrophoresis (PAGE) was used to determine proteins present in estrus-associated and nonestrus-associated equine oviductal fluid as compared to blood serum from the same mares. Oviductal fluid volumes increased significantly during estrus to an average of 3.94 ml/24 hr from 1.44 ml/24 hr during nonestrus. Total oviductal protein increased significantly from 24.6 mg/24 hr during nonestrus to 53.9 mg/24 hr during estrus. One-dimensional PAGE demonstrated that the proteins in equine oviductal fluid were present throughout the cycle and also common to equine serum. Reducing conditions revealed one band at 106 kDa detected only in nonestrus-associated oviductal fluid, while nonreducing conditions revealed bands at 48 and 25 kDa that were present in oviductal fluid in general. Two-dimensional PAGE demonstrated three 50 kDa proteins that were detected only in estrus-associated oviductal fluid and several 24 kDa proteins detected only in nonestrus-associated oviductal fluid. Those proteins found only in estrus-associated oviductal fluid may be vital to the fertilization process, while those found only in nonestrus-associated oviductal fluid may be vital to early embryonic development.