Effect of platelet-activating factor (PAF) on human spermatozoa-oocyte interactions

The effect of exogenous platelet-activating factor (PAF) on human spermatozoa was examined by monitoring acrosomal status and hamster oocyte penetration. Induction of the acrosome response by PAF was dose, and time, dependent and required capacitated spermatozoa. Addition of 10(-14) mol PAF l-1 enhanced the acrosome reaction eightfold compared with controls treated with human serum albumin (HSA). Similar concentrations of lyso-PAF failed to induce acrosomal loss and preincubation of spermatozoa with CV3988, an inhibitor of PAF, prevented PAF induction of the acrosome reaction. PAF significantly increased the number of zona-free hamster oocytes penetrated compared with controls (9.8 +/- 0.5 of 25 oocytes were penetrated by control spermatozoa compared with 23.3 +/- 0.8 out of 25 oocytes penetrated after incubation of spermatozoa with 10(-14) mol PAF l-1; 93% of all oocytes were penetrated by at least one spermatozoon following incubation with PAF), and also increased the number of decondensed spermatozoa found per egg during the sperm penetration assay (from 1.7 +/- 0.3 spermatozoa/egg with control spermatozoa to 3.3 +/- 0.5 spermatozoa/egg with PAF-treated spermatozoa). PAF-induced increases in acrosome reaction and sperm penetration assay values were similar to effects obtained with human follicular fluid and were calcium dependent. Induction of the acrosome reaction by physiological concentrations of PAF appeared to be morphologically similar to the response induced by follicular fluid as assessed by electron microscopy.