Quantitative assessment of the serum-induced stimulation of human sperm motility

In previous studies, sperm populations with high motility and fertilizing potential have been isolated using Percoll gradients and/or addition of serum or caffeine, but no objective measurements of the motility parameters affected have been presented. In addition, the types of sperm populations and the incidence of positive or negative responses to these treatments have never been documented. In this paper, the proportion of samples responding positively or negatively to these treatments and the type of motility stimulation observed was measured using the CellSoft computer-assisted digital image analysis system. Semen, obtained from the Infertility Clinic, was washed on discontinuous Percoll gradients. Sperm motility parameters were measured in the original semen and after washing through a Percoll gradient in the presence or absence of serum or caffeine. Percoll washing permitted a good recovery of essentially pure sperm. The Percoll treatment had little effect on the percentage of motile sperm but caused a decrease in the linearity-related parameters. A high proportion of the washed sperm samples supplemented with serum showed an increase in at least one of the motility parameters when compared to sperm populations in the original semen (68% of cases) or after Percoll washing (96% of cases). These effects were maintained for several hours. The stimulation of motility was concentration-dependent, with an optimum around 25-30% serum. Caffeine (4 mM) increased linear velocity but lowered linearity. In contrast to caffeine, which stimulated sperm motility for less than 1 h, the effects of human serum lasted for more than 16 h.