Sperm penetration through the zona pellucida of salt-stored hamster eggs is delayed.

One of the problems in assaying sperm capacitation is that live eggs mount a block to polyspermy at the zona pellucida. To circumvent this problem, researchers have started to use salt-stored eggs to assay sperm capacitation (Boatman et al., Gamete Res 19:19-29, 1988; Yoshimatsu et al., Gamete Res 21:115-126, 1988). These researchers have demonstrated that the zonae of salt-stored eggs were penetrable by capacitated sperm, but they did not examine whether the timing of penetration of fully capacitated sperm was altered. This report shows that zona penetration by fully capacitated sperm is delayed in both short-term salt-treated eggs (2 hr) and in eggs stored in salt for > 2 days. These results indicate that the zona is modified when eggs are treated with a high-salt solution.