Studies on the dynamics of plasma androgens and on the origin of dihydrotestosterone in dogs

Testosterone and androstenedione dynamics were studied with a constant infusion technique in adult male dogs. The metabolic clearance rate (1370 ± 660 1/day) and blood production rate (1.5 ± 0.7 mg/day) of testosterone were similar to the metabolic clearance rate (1870 ± 760 1/day) and blood production rate (1.2 ± 0.3 mg/day) of androstenedione. Plasma concentrations of testosterone and androstenedione were respectively 115 ± 46 ng/100 ml and 66 ± 15 ng/100 ml. The conversion of these two prehormones to dihydrotestosterone was studied; respectively, 8.6 ± 2.2 and 1.8 ± 1.1% of plasma testosterone and androstenedione were converted to plasma dihydrotestosterone. In addition, testosterone and dihydrotestosterone were simultaneously measured in peripheral, adrenal and spermatic vein plasma. The concentration of testosterone at these three different sites was 116 ± 18, 98 ± 41 and 6620 ± 2100 ng/100 ml while the concentration of dihydrotestosterone was 34 ± 16, 79 ± 24 and 1710 ± 780 ng/100 ml. From these data, it is concluded that about 1/3 of plasma dihydrotestosterone is derived from plasma precursors while the rest arises from glandular secretion, mainly the testes.