PORCINE SPERM BINDING TO OVIDUCTAL EXPLANTS IN CULTURE

Explants taken from the mucosa of the oviductal isthmus and ampulla of gilts 15 days after mating were cultured on Matrigel-coated Millicell inserts in modified minimal essential medium (MEM) containing 70 pg/ml estradiol and 0.5 ng/ml progesterone. After two weeks, ejaculated boar spermatozoa washed in MEM were added to the explants within the inserts to a final concentration of 2 x 10(6) sperm/ml. Then the medium in the outer well surrounding the inserts was replaced with MEM containing 70 pg/ml estradiol and 0.5 ng/ml progesterone (peak systemic levels during estrus) or 2 pg/ml estradiol and 0.5 ng/ml progesterone (systemic levels during diestrus) or 0.01% dimethylsulfoxide (DMSO) carrier alone. Spermatozoa attached to the epithelial surface of the explants within minutes, and more than 70% remained motile for 42 to 44 hours. Greater numbers of spermatozoa (P < 0.05) bound to explants from the isthmus than from the ampulla. Both in the isthmus and in the ampulla, binding of spermatozoa was greater (P < 0.05) in the presence of estrus levels of steroids than in medium without steroids. These results indicate that the binding of spermatozoa to oviductal epithelium is influenced by region and hormonal status. In addition to binding to the epithelial surface, some spermatozoa were trapped in a mucous secretion produced by isthmic explants. Pronase but not trypsin, heparin or hyaluronidase was found to release spermatozoa from the mucus. Binding to epithelial surfaces and entrapment in mucus may serve to create an oviductal reservoir of spermatozoa prior to fertilization.