After mating, inseminated mammalian spermatozoa are transported to the oviduct. They attach to and interact with oviductal epithelial cells (OEC), and as a result of this interaction, a reservoir of spermatozoa forms in the oviduct. In several species, the reservoir has been shown to be limited to the caudal isthmus, and spermatozoa are held there until ovulation when a small number are released to meet the eggs. One of the proposed mechanisms for the creation and maintenance of the isthmic reservoir is adherence of sperm to the mucosal surface. The binding of sperm in the isthmus appears to be quite strong, since repeated flushing is required to release bound sperm in situ, and enzymatic treatment of oviductal explants is unsuccessful for releasing sperm. Attachment and release of spermatozoa from the reservoir likely plays a role not only in the temporal coordination of fertilization but also in assuring that the appropriate number of spermatozoa arrive at the site of fertilization in the appropriate condition.
Attachment to oviductal epithelial explants and cultured monolayers of oviductal epithelium appears to extend the life of sperm in vitro. The process of capacitation, along with the switch to the hyperactivated flagellar beating pattern, appears to coincide with the ability of sperm to be released from the oviductal reservoir. Noncapacitated hamster sperm injected into the oviduct bind to the epithelium, while those that have been capacitated in vitro remain free.