Influence of purified plasma proteins on testosterone uptake and metabolism by normal and hyperplastic human prostate in "constant-flow organ culture".

Surgical samples of human prostate were explanted and submitted to constant-flow organ culture. The medium contained 3H-testosterone 50 nM, and except for controls, increasing concentrations of human serum albumin (HSA) or human sex-steroid-binding plasma protein (SBP). At steady state, the explants were washed and homogenized, and the total radioactivity, radioactive testosterone, androstanolone (17 beta-hydroxyandrostan-3-one), androstane-3 alpha, 17 beta-diol, and androstane-3 beta, 17 beta-diol were determined after the addition of the corresponding internal 14C standards. From these data, testosterone uptake and metabolism were quantitated. The concentration of unbound testosterone in protein-supplemented culture media was measured separately by equilibrium dialysis. In control superfusions without protein, the tissue concentration of total radioactive steroids was equivalent to 182 +/- 18 (mean +/- SEM) pmoles/g of prostate. Androstanolone represented about 2/3, testosterone 1/10, and the two androstanediols together 1/10 of the total radioactivity. No difference was found between "normal" and hyperplastic prostate explants. In experiments with HSA (15-176 muM), is was observed that the uptake of radioactive testosterone in the prostate explants was decreased in direct proportion to the unbound testosterone fraction of the superfusion medium, but the proportions of testosterone metabolities in the superfused explants remained the same. In experiments with SBP (6-135 nM), the concentrations of unbound testosterone in the superfusion medium were reduced to the same levels as in the experiments with HSA. The reduction of tissue radioactivity was somewhat larger than that expected from the reduction of unbound testosterone in the superfusion medium for the concentrations of SBP less than 50 nM, and then remained approximately constant. In addition, SBP altered the metabolism of testosterone: the androstanolone/testosterone ratio in the prostate explants was critically dependent upon the SBP concentration in the superfusion medium. It is therefore suggested that, independent of its effect on the binding of testosterone, SBP has a direct effect on testosterone uptake and metabolism by the human prostate. The underlying mechanism is unknown.