Chemical composition and protein source in the capacitation medium significantly affect the ability of human spermatozoa to undergo follicular fluid induced acrosome reaction*

We studied the effect of media composition on sperm capacitation, using Biggers-Whitten-Whittingham (BWW) medium, Ham's-F10 and a modified Tyrode's medium (HSM) supplemented with bovine serum albumin (BSA) or fetal cord serum (FCS). We evaluated the effect of chemical environment and protein supplementation on the sperm motion parameters of curvilinear velocity and linearity, and on the ability of incubated spermatozoa to undergo follicular fluid induced acrosome reaction. Neither chemical composition nor protein supplementation of capacitation media greatly affected motion parameters after 2 h incubation. Furthermore, chemical composition had only a small effect on the ability of spermatozoa to undergo the acrosome reaction upon exposure to follicular fluid. A higher proportion of spermatozoa underwent acrosome reaction after incubation in HSM (8% control (C); 28% follicular fluid) than in BWW (8% C, 17% follicular fluid) or Ham's F-10 (6% C, 19% follicular fluid). By contrast, protein source proved critical in determining acrosome reaction inducibility. Spermatozoa incubated in BSA-supplemented media showed a 4-fold increase in acrosomal discharge when exposed to follicular fluid (6% C, 22% follicular fluid) compared to controls while spermatozoa incubated in FCS were unable to undergo acrosome reaction (6% C, 6% follicular fluid). Simultaneous addition of FCS to BSA capacitation medium blocked acrosome reaction inducibility and the late addition of BSA, after sperm incubation in FCS, did not facilitate acrosome reaction. We propose that an inhibitor of sperm capacitation is present in FCS and therefore, the selection of optimum incubation conditions for spermatozoa may be of critical importance when evaluating or treating infertile patients.