What functions of the sperm cell are measured by in vitro fertilization of zona-free hamster eggs?

Human spermatozoa were capacitated in media containing either high concentrations (3.5%) of human serum albumin (HSA) or low concentrations (0.3%) of bovine serum albumin (BSA). The effects of both capacitation media were assessed immediately and after overnight preincubation (18 to 24 hours) by adding a mixture of nonliving human oocytes and living zona-free hamster eggs to the sperm suspension. Overnight preincubation of sperm in media containing 3.5% HSA enhanced sperm fusion with hamster vitelli, but the capacity for zona penetration was lost. These effects could be attributed to the concentration of HSA rather than a general effect of albumin concentration, because overnight preincubation in 3.5% BSA did not interfere with zona penetration. During overnight incubation in 3.5% HSA, the percentage of acrosome reactions increased, as did alterations in the equatorial segment of the acrosome-reacted sperm. The percentage of motile sperm remained high after overnight incubation in 3.5% HSA, but both the mean swimming speed and flagellar activity on the zona surface declined. The sperm also lost their ability for strong zona binding after overnight incubation in 3.5% HSA.