Acrosomal status of mouse spermatozoa in the oviductal isthmus.

The principal purpose of this study was to establish the acrosomal status of mouse spermatozoa stored in the isthmus of the oviduct after natural mating. Scanning electron microscopy of oviducts fixed about 6 hr before the estimated ovulation time showed numerous acrosome-intact spermatozoa attached to the mucosal surface of the oviduct, or trapped in the oviductal crypts. Nevertheless, an unambiguous assessment of the state of the acrosome requires transmission electron microscopy. Using this method, it was observed that the acrosome was intact in the 81% of spermatozoa attached to the mucosal surface but in only 31% of spermatozoa that were free in the lumen. Most of the free spermatozoa showed swelling or disruption of the acrosome. This result might indicate that the in vivo spermatozoon-oviductal mucosa interaction maintains the acrosome intact. Alternatively, it could mean that only ejaculated spermatozoa with a normal acrosome can establish such a mucosal relationship.