Androgen concentrations in testicular and peripheral blood in the male Japanese quail

Two experiments were conducted in which the concentrations of testosterone and dihydrotestosterone (DHT), an active metabolite of testosterone, were studied in the general circulation and in the testicular effluent. In the first experiment, blood samples taken from adult male quail were analyzed by radioimmunoassay for androgen and DHT concentrations; from these data, testosterone concentrations were calculated. The average concentration of androgen was 4238 pg/ml plasma. The average ratio of DHT/testosterone was .75. In the second experiment, steroid concentrations were compared in blood samples taken from the testicular vein and from the general circulation. Androgen concentrations in the general circulation were 36% of that obtained for the testicular effluent. In addition, testosterone and DHT concentrations in the general circulation were 36 and 46%, respectively, as high as concentrations in the testicular vein. Comparison of the average ratios of testosterone/DHT in the general versus testicular plasma revealed a higher ratio in the general circulation (.73 vs. .51, respectively). These results provide additional evidence for testosterone as the major male steroid secreted by the gonads. In addition, the relative concentration of DHT in the quail, which is higher than documented for most species, was higher in the peripheral than in the testicular circulation. This may indicate peripheral metabolism of testosterone to its active metabolite, DHT, and could have implications as to the availability of DHT for its target tissues.