Kinetics of [1,2-3H]-testosterone metabolism in normal adult male rats: effects of estrogen administration☆

Abstract Following the subcutaneous administration of [ 3 H]-testosterone to adult male rats, the levels of tritium as labelled testosterone, 5α-dihydrotestosterone and 5α-androstanediol in the methylene chloride extracts of blood, muscle, prostate, seminal vesicles and liver were determined at serial time intervals (15–240 min). Results were obtained for control animals and ones which had received 100μg 17β-estradiol valerate intraperitoneally per day for 4 days. From the whole tissue and methylene chloride extract counts, it is apparent that most of the radioactivity in the prostate and seminal vesicles is present in unconjugated metabolites while in the blood and liver significant fractions were in conjugated metabolites. With the exception of the liver, estradiol administration caused an increase in the radioactivity in each of the three compounds in the tissues. In both groups of animals, labelled 5α-dihydrotestosterone was predominant in the prostate and seminal vesicles while labelled testosterone predominated in the blood and muscle. In the control animals, labelled testosterone and 5α-dihydrotesterone were present in similar amounts in the liver; in the rats receiving estrogen, labelled 5α-dihydrotestosterone was present in lower amounts than in the control animals.