Factors affecting sperm motility. IV. Incubation of human semen with caffeine, kallikrein, and other metabolically active compounds.

The effect of six metabolically active compounds, namely caffeine, kallikrein, cyclic adenosine 3':5'-monophosphate, prostaglandin E, triiodothyronine, and insulin on spermatozoal motility was investigated. Hypokinetic and normokinetic semen specimens from fertile and infertile patients were incubated with various concentrations of these compounds. Spermatozoal velocity and percentage of motility were determined periodically with the objective multiple exposure photography (MEP) method before and during the following 4 to 8 hours. No significant differences was found between experimental and control specimens as to these parameters under the influence of the tested compounds, with the exception of caffeine. Caffeine immediately increased the percentage of motile spermatozoa by 30% to 50% of initial values in approximately two-thirds of cases. No influence on sperm velocity was detected during this period. By using the combined MEP and supravital staining techniques it was found that nonmotile live spermatozoa were activated by caffeine without any effect on the percentage of dead sperm. Some practical implications of these findings, the difference between our results and those reported by others, and the mechanism of action of these compounds are reviewed and discussed.