Summary. The ability of spermatozoa recovered from the successive segments of the hamster epididymis to bind to the zona pellucida was studied and a major increase was found as spermatozoa passed from the proximal to the distal portions of the corpus epididymidis (1·95 compared with 20 spermatozoa bound/egg). Tubules from the proximal epididymis were cultured in conditions which preserved the motility of the contained spermatozoa for 48–72 h. Addition of 2 μm-5α-DHT to the culture medium for 17 h stimulated the incorporation of 3H-labelled amino acids into several protein bands whose mobility in polyacrylamide gel electrophoresis was coincident with those of glycoproteins EP1–EP6, previously identified as androgen-dependent in the hamster epididymis in vivo. Examination of the material extracted from washed spermatozoa with 0·5 m-NaCl revealed the presence of radioactive proteins on spermatozoa. The zona-binding ability of spermatozoa from androgen-treated cultured proximal corpus tubules was significantly increased (P < 0·001) as was the no. of spermatozoa/egg (5·51) compared with the value for control cultures (0·87 spermatozoa/egg).
We suggest that androgen-dependent epididymal secretory proteins that associate with spermatozoa might participate in the formation or activation of a site for zona pellucida recognition in the sperm surface.