Publication Abstract

Excretion of free and conjugated steroids in rainbow trout (Oncorhynchus mykiss): evidence for branchial excretion of the maturation-inducing steroid, 17,20beta-dihydroxy-4-pregnen-3-one

Excretion of free and conjugatedsteroids in rainbow trout (Oncorhynchus mykiss): evidence for branchial excretionof the maturation-inducing steroid, 17,20β-dihydroxy-4-pregnen-3-one

E.L.M. Vermeirssen and A.P. Scott

Thegoal of this study was to identify excretory routes of three main steroids produced bysexually mature male and female rainbow trout: 17,20β-dihydroxy-4-pregnen3-one (17,20β-P), sulfated 17,20β-P (17,20β-P-S), and testosterone glucuronide (TG). Spermiating males ormaturing trout were cannulated via the dorsal aorta and urinary bladder and injected withtritiated steroids. Blood, water, and urine were sampled over the next 12 hr when the fishwere killed and bile was collected. The identities of the excreted products weredetermined by anion-exchange chromatography, reverse-phase highperformance liquidchromatography, enzyme hydrolysis, acid solvolysis, microchemical modification, andthin-layer chromatography. Following the injection of tritiated 17,20β-P, 25% of the radioactivity rapidlyappeared unmodified in the water; 15% appeared slowly in the urine, mainly as 17,20β-P-S; and 40% was recovered inthe bile, mainly as 17,20β-P-glucuronide. 17,20β-P was shown to be released into the water via the gills. Over the12-hr sampling period, 20% of the 17,20β-P released into the water was taken up again by the fish (alsobranchially). A mathematical analysis showed that 40% of the 17,20β-P would have been released into thewater in the absence of uptake. Following the injection of tritiated 17,20β-P-S, 63% appeared veryrapidly, in an unmodified form, in the urine, and 15% was recovered in the bile. Followingthe injection of tritiated TG, 9% appeared slowly, mainly untransformed, in the urine, and59% was recovered in the bile. These results show that the three types of steroids arereleased into the water by three different routes: free steroids, gills; sulfatedsteroids, urine; and glucuronidated steroids, bile.

Reference:

E.L.M. Vermeirssen and A.P. Scott, 1996. Excretion of free and conjugated steroids inrainbow trout (Oncorhynchus mykiss): evidence for branchial excretion of thematuration-inducing steroid, 17,20b-dihydroxy-4-pregnen-3-one. General and ComparativeEndocrinology 101, 180-194.

E.L.M. Vermeirssen* and A.P. Scott*

General and Comparative Endocrinology 101, 180-194