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Estimating the Contribution of the Prostate to Blood Dihydrotestosterone

Department of Endocrinology/Andrology, Vrije Universiteit University Medical Center (A.W.F.T.T., L.J.G.), 1007 MB Amsterdam, The Netherlands; and Department of Andrology, Concord Hospital and ANZAC Research Institute, University of Sydney (S.K., M.J., D.J.H.), Sydney, New South Wales 2139, Australia

Address all correspondence and requests for reprints to: Prof. D. J. Handelsman, ANZAC Research Institute, Sydney, New South Wales 2139, Australia. E-mail: djh{at}anzac.edu.au.

The prostate strongly expresses type 2 5-reductase, which avidly converts on entry most testosterone (T) to 5-dihydrotestosterone (DHT). However, the quantitative contribution of the prostate to blood DHT is uncertain. We evaluated prostatic contribution to blood DHT by comparing the blood DHT concentrations in androgen-deficient patients with or without a prostate while they were receiving standard dose of T replacement. Androgen-deficient males (ADM) and female to male (F2M) transsexuals were studied in 2 centers, with both groups receiving either testosterone ester injections (250 mg mixed T esters) every 1 wk (Amsterdam) or 800 mg subdermal T implantation (Sydney). Among 39 Dutch patients, F2M (n = 21) were younger and smaller in physique than ADM (n = 18). One week (±1 d) after an injection, plasma DHT concentrations were 1.6 ± 0.2 (F2M) vs. 1.4 ± 0.2 (ADM) nmol/liter (P = 0.47), but the postinjection time interval to blood sampling was shorter in F2M (5.9 ± 0.4 vs. 7.2 ± 0.3 d; P = 0.01). Covariance adjustment for time since last injection, age, and physique did not change the lack of significant difference in postinjection plasma DHT concentration. The rapid and wide excursions in plasma T concentrations after an im T ester injection make the timing of blood sampling critical. To remove confounding by this variable, the experiment was repeated at a second site in similar patients, but using a depot T that achieves steady-state delivery for prolonged periods. Among 29 Australian patients, before and 1 month after subdermal implantation of 800 mg T, plasma DHT concentrations were not significantly different between groups [F2M, 1.1 ± 0.1 (n = 14); ADM, 1.3 ± 0.1 (n = 15); P = 0.28]. Correction for covariates, including age, height, weight, body surface area, and body mass index, did not influence the lack of significant difference between treated groups. As both modes of T administration yielded similar plasma DHT concentrations regardless of the presence of a prostate, this study indicates that the normal human prostate is not a major contributor to circulating blood DHT concentrations.

Abbreviations: ADM, Androgen-deficient males; BMI, body mass index; BSA, body surface area; DHT, 5-dihydrotestosterone; F2M, female to male; T, testosterone.

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