The hardening effect of dimethylsulphoxide on the mouse zona pellucida requires the presence of an oocyte and is associated with a reduction in the number of cortical granules present.

When mouse ovulated oocytes were exposed to 1.5 M-dimethylsulphoxide (DMSO) the resultant hardening of the zona pellucida was not a direct effect but required the presence of an oocyte. The hardening of the zona pellucida when zonae used were aged in vitro was also dependent upon the presence of the oocyte. Protocols of DMSO exposure that induce zona-hardening also caused depletion of the numbers of cortical granules underlying the oocyte surface, whereas protocols without effect on the zona did not reduce significantly the cortical granule count. It is proposed that the effects of DMSO may be mediated by a release of cortical granule contents.