Effect of caffeine and kallikrein on cryo-preserved human spermatozoa.

Preservation of human semen in liquid nitrogen causes a significant impairment of sperm motility. Ejaculated human spermatozoa show an increased motility in the presence of caffeine, a phosphodiesterase inhibitor, and pancreatic kallikrein (EC 3.4.21.8), a kinin-producing proteinase. Hence, the effect of both substances on post-thaw motility, fructose consumption, and cervical mucus penetration of cryo-preserved human spermatozoa was investigated. The results indicate that both substances stimulate the motility of freshly ejaculated spermatozoa and also improve the motility pattern of cryo-preserved human spermatozoa, thus offering a possible means of improving the quality of freeze-preserved human semen.