Distribution and Metabolism of3H-testosterone in Castrated Male Rats; Effects of Cyproterone, Progesterone and Unlabeled Testosterone

The effect of immediate pretreatment with cyproterone, progesterone and unlabeled testosterone on the distribution and metabolism of 3H-testosterone in mature, castrated male rats was investigated. One hr after its intravenous administration, 3H-testosterone was rapidly metabolized such that only 30% of the radioactivity in plasma remained as testosterone, the major portion consisting of polar metabolites. The concentrations of 3H-testosterone in seminal vesicle and pituitary were 10 and 3 times greater than plasma, respectively. Even larger amounts of 3H-dihydrotestosterone (DHT) accumulated in these tissues, the respective concentrations being 200 and 30 times greater than plasma. Testosterone and DHT concentrations in seminal vesicle and pituitary were markedly inhibited by pretreatment with cold steroids. Progesterone, but not cyproterone or unlabeled testosterone, reduced the ratio of DHT to testosterone in the seminal vesicle. Hypothalamic and cerebral concentrations of 3H-testosterone were similar ...