Shinohara Y, Baba S, Kasuya Y
J Clin Endocrinol Metab. 1980 Dec;51(6):1459-62. doi: 10.1210/jcem-51-6-1459.
A mass fragmentographic method employing stable isotopically labeled testosterone was employed to follow the time course of urinary excretion of the two main testosterone metabolites, androsterone glucuronide and etiocholanolone glucuronide, in humans after the oral administration of 20 mg testosterone-19.19.19-d3. The results indicate that the extensive metabolism of testosterone in the liver could be the reason that the orally administered testosterone appeared in the circulation only in small amounts, even though testosterone was completely absorbed from the gastrointestinal tract.
