Androgen Metabolism by Rat Epididymis: Metabolic Conversion of3H-Dihydrotestosterone In Vivo and In Vitro

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Abstract
Following intramuscular injection of functionally hepatectomized 24-hr castrated rats with tritiated 5α-androstane- 17β-ol-3-one (3H-DHT), the androgenic metabolites found in the different segments of epididymis were qualitatively similar to those formed after incubation in vitro. Approximately 50% of the radioactivity consisted of unmetabolized DHT in both experiments. In the in vivo investigation, 5α-androstane-3α-ol-17-one (androsterone) and 5α-androstane-3α,17β-diol (3β-diol) were the main metabolites, each constituting approximately 10% of the total radioactivity. In addition, 5α-androstane-3β,17β-diol (3β-diol), 5α-androstane-3,17-dione (5α-A-dione), some A16 compounds, and a large polar fraction were demonstrated. No significant difference in the metabolic pattern was observed between caput and cauda epididymidis. After incubation in vitro, androsterone was undetectable in the caput and only negligible amounts were present in the cauda epididymidis. 3α-Diol was the main metabolite in both the caput (43%) and the cauda (24%). Other metabolites were similar to those found in the in vivo investigation. The main metabolites found in both blood and muscle were 3α-diol (approximately 40%) and androsterone (approximately 20%). About one-third of the radioactivity consisted of polar metabolites and only insignificant amounts of DHT could be detected. 3α-Diol was also the main metabolite (59%) when the in vitro metabolism of 3H-DHT was examined in muscle tissues. Approximately one-third of the radioactivity was characterized as 3H-DHT. Furthermore, androsterone was not detected, and only small amounts of polar metabolites were present. Investigation of the nuclear pellet from the caput epididymidis after in vivo experiments demonstrated uptake of DHT only. This finding suggests that, as is the case in the prostate, DHT is an important mediator of androgenic action in the rat epididymis.