Changes in the motility pattern of human spermatozoa during in vitro incubation

Suspensions of capacitating human spermatozoa were analyzed for movement characteristics using high-speed videomicrography. The status of the acrosome reaction was also assessed by the zona-free hamster ova penetration test. (1) Movement characteristics of human spermatozoa were classified into 4 types (A, B, C, D). Type A: The movement was active, but its progressive orientation was irregular. Type B: The spermatozoa moved with a wide amplitude of the end of tail. Type C: The amplitude of the tail decreased, and the linear velocity of progression increased. Type D: The whole part of tail showed wavelike rhythmical movements, and the velocity more increased. (2) Movement characteristics of human spermatozoa in vitro gradually changed from Type A to B, C and D. As the spermatozoa classified Type D moved very powerfully and this motility pattern was obviously different from the other types, it was considered hyperactivation of human spermatozoa. The Type D was found from 2 or 3 hr of incubation, and after 3 or 4 hr most of the spermatozoa showed Type D. (3) The motility pattern of human spermatozoa changed to the Type D before the spermatozoa penetrate into zona-free hamster oocytes. It suggested that the hyperactivation occurred before the acrosome reaction takes place.