Release of a factor during early stages of contact between hamster sperm and eggs in vitro

A sensitive bioassay was devised which detected the release of a factor resulting from contact between the surfaces of sperm and zona pellucida of the golden hamster in vitro. This assay is based upon the ability of the factor to induce premature binding between the gametes. Release of the factor occurred in a dose‐dependent manner as a function of increasing concentration of sperm, but only after they were capacitated, i.e., subjecting sperm to those conditions which endow them with the ability to penetrate the egg. The factor was released, in what appeared to be pulses of activity, throughout the 40‐minutes prepenetration period, and this release culminated in a large pulse which was rapidly terminated soon after penetration began. The factor was also detected following contact with homologous zonae pellucidae from which the vitellus had been mechanically removed. Thus, factor release and cessation of its release occurred independently of the vitellus. When hamster eggs or isolated zonae were replaced by those of the mouse, the factor was not detected even though hamster sperm attached to them; nor was it recovered when isolated zonae or eggs of the hamster were treated with trypsin before exposure to sperm. Factor release and penetration of eggs were inhibited in a similar manner as a function of increasing concentrations of trypsin. This finding and the observation that the factor was not detected when the sperm were not capacitated, and therefore incapable of penetration, suggests that a relationship may exist between factor release and penetration.