The motility and fertility of golden hamster sperm cultured in BSA-free medium.

Before fertilization, capacitation and the acrosome reaction in mammalian spermatozoa must be completed. The motility and fertility of hamster sperm were examined in four kinds of modified Tyrode's solution with or without bovine serum albumin (BSA). Since the presence or absence of polyvinylalcohol (PVA) in the media was another variable, its effect on the sperm motility and fertility was also studied. Sperm were incubated in four different media for up to 6 h at 37.5 degrees C. After 4 h of incubation in the media containing BSA alone or BSA and PVA, sperm were hyperactivated, showing a high sperm motility index (SMI) and were able to fertilize more than 80% of eggs. However, their fertility rapidly decreased during further incubation. In contrast, sperm in the medium containing PVA and no BSA showed low SMI scores after 4 h. However, during the following 2-h period, the SMI progressively increased and sperm were hyperactivated. Furthermore, the hyperactivated sperm in the PVA containing medium were able to effectively fertilize eggs. Our results indicate that hamster sperm can be capacitated in BSA-free medium and that capacitation occurs much more slowly in such a medium. We suggest that PVA is a reasonable alternative to BSA in in vitro fertilization and that this slowly progressing system may be a good model for studying various steps in sperm activation.