Formation in Vivo of 5 α -Dihydrotestosterone by the Canine Epididymis 1

The metabolism in vitro of androgenic steroids by epididymal tissue has been studied in various species (1-3). When testosterone (T) was the substrate, significant quantities of 5_α-dihydrotestosterone (DHT) were produced (1). It is well known that DHT shows more androgenic effects than T in many systems of bioassay and could thus be more important physiologically than T. Furthermore, evidence has been presented concerning the biological activity of other reduced metabolites of T (4) and it is clear that some of these metabolites are far from inactive (4). Since the physiological significance of an organ can only be determined by experiments in vivo and in vitro (5) we have devised a method to examine the epididymal metabolism of ³H-T following infusion via the epididymal artery. Data on ³H metabolites of T in epididymal tissue and in epididymal venous blood plasma are presented in the current communication.

Materials and Methods. Experiments were performed on healthy, mongrel, mature, male dogs weighing between 17 and 24 kg. The animals were anesthetized with sodium pentobarbital (30 mg/kg, iv) and a cannula was placed in the left femoral artery.

The initial preparation of the epididymis for infusion via the epididymal artery was as described for the infused testis (6). The epididymal artery was dissected out and a 27 gauge needle, attached to a plastic cannula, was inserted into this artery. The testis was then removed and the epididymis was freed of all testicular tissue. The isolated epididymis was now placed in a metabolic chamber (6) and infused with the dog's oxygenated, arterial blood via the cannula in the epididymal artery. The constant flow of arterial blood was 0.78 ml/min. After a 30 min “warm up” period (6), the experiments started adding ³H-testosterone (sp act 54.8 mCi/μmole), dissolved in 0.9% sodium chloride, to the blood in the epididymal artery at a constant rate of 0.05 μCi/min.