Efficient capacitation of hamster spermatozoa can be induced by follicular fluid (Barros & Austin, 1967; Yanagimachi, 1969a, b) and blood sera of several species (Barros & Garavagno, 1970; Yanagimachi, 1970a; Talbot, Franklin & Fussell, 1974). Two components are involved: one is dialysable, heat-stable and stimulates sperm motility, while the other is non-dialysable, heat-labile and induces the acrosome reaction (Yanagimachi, 1969a). Our understanding of capacitation and the acrosome reaction might be enhanced if the nature and mode of action of these factors were known. Blood serum is an easily available source of both factors and this preliminary report describes the recovery of the sperm motility-stimulating activity from human serum.
Fresh human serum was heated to 56°C for 30 min to destroy unidentified toxic factor(s) (Yanagimachi, 1970a). The serum was chromatographed on Sephadex G-25 (medium grade) and equilibrated in Tyrode's solution supplemented with 0·33 mm-sodium pyruvate, 0·01 mg phenol red/ml,