Caffeine- and kallikrein-induced stimulation of human sperm motility: a comparative study.

Stimulation of human sperm motility by caffeine and kallikrein was compared in the same semen material. Caffeine, a cyclic nucleotide phosphodiesterase inhibitor, induced an immediate stimulation of sperm motility the intensity being relatively constant during the first two hours of incubation. Kallikrein, a kinin-releasing proteinase, induced a similar enhancement of total sperm motility, but showed a delayed type of reaction with maximum stimulation at 2 hours of incubation. In contrast to the effect of caffeine lasting some hours, enhancement of sperm motility induced by kallikrein was observed 24 hours. Simultaneous addition of serum (kininogen source) and kallikrein to semen samples led to a sitmulation of total sperm motility with higher mean values than those obtained by caffeine of kallikrein alone. However, the ratio of spermatozoa with very good forward progression was highest during caffeine stimulation. Simultaneous addition of caffeine and kallikrein led to a further improvement of sperm motility which was significantly above that produced by caffeine or kallikrein alone. This observation and the finding of a different response of the spermatozoa of two ejaculates towards caffeine of kallikrein indicate that caffeine (cyclic AMP) interferes quite differently in comparison to kallikrein (kinins) in stimulating sperm motility.