Summary. The

No abstract

Capacitated golden hamster spermatozoa bound to the inner wall as to the outer surface of the zona pellucida, suggesting that the receptor-for-spermatozoa may occur throughout this egg envelope. When solutions of hamster zonae pellucidae were prepared by heating zonae in an aqueous buffer, receptor activity was retained and was stable to boiling. The addition of such solutions to capacitated spermatozoa (5 zonae/mul) prevented them from binding to eggs and fertilizing them. Solubilized mouse zonae were also partly effective, as would be predicted from the limited crossbinding between mouse and hamster gametes. Receptor activity was lost following the zona reaction.

Bovine zonae were solubilized by heating t o 80°C in buffered saline. On injection of female rabbits with this solution, zona-specific antisera were produced that could be assayed on bovine eggs in vitro by immunofluorescence, coating, and inhibition of sperm-binding. When the latter was complete, the rabbits were found to be infertile. Immunofluorescence assays showed that the rabbit anti-bovine zona serum reacted as strongly with rabbit and rhesus monkey zonae as with homologous zonae. Strong cross-reaction was also observed with marmoset and dog zonae, but with hamster zonae the reaction was relatively weak. Key words: zona pellucida, contraception I N TRODU CTI ONIn previous experiments we demonstrated that the sperm receptor in the zona pellucida of the hamster egg is inactivated by certain proteases, although it is resistant t o others, eg, collagenase [Gwatkin, 19781 . On heating t o 65°C the zonae dissolve and on cooling they remain in solution. The solutions retain receptor activity that can be assayed by the ability of the zona material t o bind t o capacitated hamster spermatozoa [Gwatkin, 19781 and to block the fertilization of hamster eggs in vitro [Gwatkin and Williams, 19771. When used as a vaccine t o immunize mice, hamster zona solutions elicit the production of anti-zona antibody and produce a complete block t o fertility [Gwatkin, Williams, and Carlo, 19771. In order to study further the nature of the mammalian sperm receptor and of the contraceptive antigen, we are isolating a number of zona components in relatively large quantities from calf ovaries (see Gwatkin et a1 [ 19781 ). As part of this program we have also physically isolated calf zonae from follicular eggs, determined their heat solubility,

Summary. Before fertilization, the protease present within the cortical granules of the hamster egg is relatively stable to heat. Once discharged into the medium, however, it is extremely heat sensitive, undergoing inactivation even at 37\s=deg\C. Thus, body temperature would be expected to prevent the zona reaction of one egg from rendering neighbouring eggs infertile.Previous studies (Gwatkin, Williams, Hartmann & Kniazuk, 1973) showed that the zona reaction of the hamster ovum is produced by a cortical granule protease, which inactivates the species-specific receptor-for-spermatozoa located in the zona pellucida. This receptor was earlier shown to be sensitive to low concentrations of pancreatic trypsin (Hartmann & Gwatkin, 1971