[A new method for evaluating sperm fertilizing ability using the percentage of acrosome-reacted spermatozoa]

To reveal the usefulness of Ca ionophore A23187-induced acrosome reactions (AR) in evaluating sperm fertilizing ability, the relationship between the percentage of AR and the results of the hamster test was examined in 65 men. Acrosome reacted spermatozoa were classified as type A (with FITC-PSA stain at the equatorial segment) or type B (without stain) and as alive or dead by staining with Hoechst 33258. The main results were as follows. 1. During the insemination period of 3 hours with zona-free hamster oocytes, sperm motility and the percentage of live type A spermatozoa (%AR) decreased significantly (p < 0.01). 2. Among the parameters examined, the %AR in the inseminating suspension exhibited the closest correlation with the sperm penetration rate (SPR) in the hamster test. 3. Among the 27 men with a %AR of less than 5%, 20 men (74.1) had SPRs less than 30%, indicating abnormal sperm fertilizing ability. In contrast, among the 19 men with %AR of 10% or more, 16 men (84.2%) had a SPR of 100%. These results suggest that the ionophore-induced acrosome reaction (AR) well predicts sperm fertilizing ability. We propose new criteria using %AR as follows: abnormal, < 5%; borderline, 5-10%; normal, > or = 10%.