Cortical and zona reactions of heat-activated mouse eggs

Oocytes collected from superovulated Swiss albino mice were activated by heat-shock and/or fertilized in vitro. Electron microscopy showed that the cortical reaction in heat-treated eggs was incomplete. Digestion of the zona pellucida of untreated, heat-treated and fertilized eggs by pronase showed that zona pellucida hardening did occur but was weaker in heat-treated than in fertilized eggs. Fertilizability of heat-treated eggs decreased 1.5 h after heating. We concluded that, in heat-activated eggs, changes occur at the zona and plasmalemma but they are not identical with those in fertilized eggs.