Androgen-binding activity in the human testis and epididymis

The quantitation of androgen-binding activity in human testes, epididymides, and serum is reported and compared with that of similar tissue in the rat. By using steady-state polyacrylamide gel electrophoresis and a tritiated 0.5 nM testosterone label, values for specific binding activity, reported as picomoles per milligram of protein, were found to be 0.21 +/- 0.01 in normal human, epididymides, 0.03 in testes, and 0.44 +/- 0.07 in human serum. Tissues from men receiving exogenous estrogen were also similarly analyzed and found to possess significantly higher androgen-binding activity: 4.10 +/- 0.48 pmoles/mg of protein (epididymides), 4.01 (testes), and 5.63 +/- 1.15 (serum). Since man possesses a sex steroid-binding globulin, attempts were made to differentiate Ion-exchange chromatography, steroid specificity, and dissociation half-time determinations were suggestive but did not conclusively demonstrate the existence of two distinctly different androgen transport macromolecules in man.