Epididymal proteins mimic the androgenic effect on zona pellucida recognition by immature hamster spermatozoa

The increase in zona pellucida binding caused by the exposure of cultured proximal corpus epididymidis to 2 microM-5 alpha-DHT (0.87 and 4.29 spermatozoa/egg for control and 5 alpha-DHT group respectively) was lost when 20 microM-cycloheximide was also added to the medium (0.72 spermatozoa/egg). These results were interpreted as meaning that de-novo protein synthesis was required to obtain the effect of androgens. When a fraction enriched in epididymal glycoproteins EP2-EP6 (18% total protein in epididymal cytosol and 30% in enriched fraction) and depleted of androgens (less than 120 pg testosterone + DHT/ml) was added to the cultured epididymal tubules, the zona pellucida-binding ability of the contained spermatozoa increased from 0.55 in controls to 2.73 spermatozoa/egg in the extract-treated group (P less than 0.02). When the enriched fraction was prepared from epididymides of 30-day castrates, the stimulatory effect was lost (1.04 spermatozoa/egg). We suggest that proteins synthesized in the epididymis are required to obtain the effect of androgens and that the glycoproteins EP2-EP6 may be involved.