Androgen metabolism in the dog

Abstract

The metabolism of four androgenic compounds, testosterone (T), androstenedione (A), epitestosterone (epi-T) and testosterone glucuronide (T-gl) was studied in the dog. All were predominantly excreted via the biliary route, and since the urinary excretion in intact and biliary fistula dogs was similar, there was an apparent lack of any significant enterohepatic circulation. The metabolism of T was somewhat different from that of A, with indications that the bulk of T is converted to A. All four compounds were preponderantly excreted as glucuronides. Five metabolites of T in bile, i.e., epiandrosterone, eticholanolone and three epimeric androstanediols (5α/3β,17β; 5β/3α,17β and 5β/3β,17β) were identified. The first three compounds were also found to be metabolites of A. Epi-T underwent reduction (5α-androstane-3β,17β-diol) and hydroxylation in ring A and 17-hydroxy oxidation. Radioactivity associated with administered T-gl was eliminated rapidly from the body. Even though the 17α-androgens may be important in canine prostatic physiology, the present study points to the insignificance of the 17α-pathway in the systemic metabolism of T and A.