Effect of caffeine and of pentoxifylline on the motility and metabolism of human spermatozoa.

Human spermatozoa were washed and incubated with 6 mM-caffeine or 0.15-1.2 mM-pentoxifylline. Sperm motility was measured by time-lapse photography, the rate of glycolysis by the release of tritiated water from 1 mM-[3-3H]D-glucose and the rate of mitochondrial respiration by the release of 14CO2 from 1 mM-[U-14C]-L-lactate or 1 mM-[2-14C]pyruvate. Caffeine stimulated the majority of spermatozoa to convert from the 'rolling' to the 'yawing' mode of progression with a concomitant increase in lateral head displacement from 4.1 +/- 0.09 microns (343) to 6.7 +/- 0.25 microns (105) (mean +/- s.e.m. (number of spermatozoa)). There was a 45% decline in the percentage of progressively motile spermatozoa and a very small decrease in their velocity. Pentoxifylline had only a slight effect on lateral head displacement or percentage motility but produced a significant increase in velocity. Both compounds increased the rate of glycolysis by greater than 40% but elevated the rate of 14CO2 production to a smaller extent. The concentrations of ATP and ADP changed very little. We conclude that the glycolytic pathway in human spermatozoa can respond efficiently to changes in energy demand.