Preliminary characterization of a factor in human follicular fluid that stimulates human spermatozoa motion

Follicular fluid alters the physiology and behaviour of spermatozoa by increasing acrosome reaction, accelerating capacitation, attracting the spermatozoon and enhancing vigorous motion of the cell. The objective of this study was to characterize the factor(s) in human follicular fluid that causes vigorous spermatozoa motion. Follicular fluid and its fractions were tested for stimulation of spermatozoa motion using a standardized assay which employs a computerized digital imaging system. Our results show that both follicular fluid and its methanol extract stimulate vigorous spermatozoa motion. To determine the characteristics of the active factor(s), the methanol extract was subjected to molecular weight fractionation, protease digestion, microcrystalline thin-layer chromatography (TLC) and C18 reverse-phase high-pressure liquid chromatography (HPLC). The spermatozoa motion stimulator in the methanol extract was dialysable against a low molecular weight membrane (1000 Da), insensitive to boiling and low pH (3.5) and was largely inactivated by proteinase K digestion. The activity was detected near the solvent front on TLC. Using reverse-phase HPLC monitored at 254 nm (UV), the activity eluted as a single peak of activity at low methanol concentration, indicating that the activity was relatively hydrophilic. The activity in the HPLC peak lost most of its motion-stimulating ability after digestion with proteinase K. The motion stimulator could be a peptide analogous to the egg-associated peptides characterized in echinoderms which stimulate spermatozoa motion, respiration and chemotaxis.