“Spontaneous” hardening of the zona pellucida of mouse oocytes during in vitro culture. II. The effect of follicular fluid and glycosaminoglycans

We have previously reported that when isolated mouse oocytes are cultured in vitro their zonae pellucidae (ZP) become increasingly resistant to solubilization by chymotrypsin (“spontaneous” ZP hardening). In the present paper we report that follicular fluid contains factors that totally prevent such hardening. Furthermore, medium conditioned by granulosa cells partially prevents hardening. The protection against ZP hardening offered by follicular fluid may be ascribed, at least in part, to its content in sulfated glycosaminoglycans heparin and chondroitinsulfate B which, when added to the culture medium at physiological concentrations, show a marked antihardening effect.