Estrogen and androgen regulation of protein synthesis by the immature rabbit epididymis.

To obtain evidence of a physiological role for androgens and estrogens in the regulation of the epididymis of sexually immature rabbits, the effects of these hormones on [35S] methionine incorporation into epididymal proteins in vitro were examined. Two-dimensional polyacrylamide gel electrophoresis revealed that short term incubation with estradiol changed the patterns of radiolabeled proteins detected in tissue homogenates of epididymal segments from castrated rabbits compared to those in segments from castrated rabbits that were not exposed to exogenous estradiol. Most of the changes seen in corpus tissue affected proteins with a wide range of pI values and relatively high mol wt (greater than 40K). The effects on caput and cauda tissue proteins were seen over a wide pH and mol wt range. Castration abolished many of the regional differences in protein synthesis; these were restored by incubation with estradiol. Testosterone had little effect on the synthesis of tissue proteins, except for stimulation of the synthesis of a single protein (17K; pI 5.1) in all three segments and stimulation of a small group of proteins (less than 14K; pI 7.0-7.2) in the corpus. Estradiol had little effect on proteins secreted by epididymal segments. Testosterone, however, stimulated the synthesis of a number of unique proteins secreted by the caput and corpus and resulted in a pattern of radiolabeled proteins similar to that obtained with intact animals. Additional secretory proteins could be stimulated in caput, but not corpus, tissue minces from intact rabbits by exogenous testosterone. No androgen-specific synthesis of secretory proteins was detected in the cauda of either castrated or intact rabbits. Estradiol affected the synthesis of both secreted and tissue proteins in terms of influencing which epididymal segment was most active at incorporating [35S]methionine into radiolabeled proteins and which was least active. Testosterone had a similar influence on secreted proteins, but did not have any analogous effect on tissue proteins. These results indicate that testosterone and estradiol influence the synthesis of proteins by the immature rabbit epididymis and that both may, therefore, be important physiological regulators of epididymal development and/or function.