Disposition and Elimination Routes of 17α-Methyltestosterone in Rainbow Trout (<i>Salmo gairdneri</i>)

Abstract

The excretion routes and tissue distribution of [ 14 C] 17α-methyltestosterone (17MT) were investigated in rainbow trout (Salmo gairdneri) after a single intragastric dose (40 μg, 126.8 kBq); about 95% of the ingested 17MT was absorbed. Total excretion 24 h after treatment accounted for 67.4% of the dose and most of this radioactivity was eliminated into the aquarium water, probably through the gills. Fecal and urinary 14 C accounted for 22 and 0.5%, respectively, of the excreted radioactivity. Three days after dosing, 23% of the ingested radioactivity was stored in the whole body and part of the residue (about 20%) was bound to tissues. No detectable amounts of unchanged 17MT were found in tissues 48 h after dosing, in liver, 17MT-derived radioactivity was present primarily as glucuronide conjugates whereas in muscle, radioactivity originated essentially from free metabolites. Maximum bile 14 C concentrations were from 200 to 2000 times the levels found in other tissues. This radioactivity was associated with glucuronide conjugates only. Excretion of 17MT-derived radioactivity occurred primarily as free metabolites in aquarium water and as glucuronide conjugates in feces. These results demonstrate the extent of biotransformation of 17MT in trout and suggest the occurrence of several metabolic pathways for this steroid in fish.