Stimulation of ejaculated human spermatozoa by caffeine.

Caffeine (1, 3, 7-trimethyl-2, 6-dioxypurine), a cyclic nucleotide phosphodiesterase inhibitor, increased the motility of ejaculated human spermatozoa. Both the percent motility and the grade of forward progression were significantly increased (P smaller than 0.001) and maintained in the presence of 6 mM of caffeine for up to five hours at 37 C. Increases in percent motility greater than two-fold occurred among the groups having low initial motility. Increases in samples with a high initial percent motility (greater than 60%) were not as dramatic, but they were still significant. In addition, the grade of motility or forward progression was increased in all groups up to one full unit. The longevity of the spermatozoa, judged by activity, was also increased for up to five hours.