In vivo uptake of radiothyroxine by the tissues of Atlantic salmon ( Salmo salar L.) parr, presmolt, and smolt

• Published in: Canadian Journal of Zoology
• Main Author: Eales, J. G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1969
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; Atlantic salmon; Salmo salar
• Online Access: http://dx.doi.org/10.1139/z69-003; http://www.nrcresearchpress.com/doi/pdf/10.1139/z69-003

Tissue uptake of radiothyroxine in Atlantic salmon parr, presmolts, and smolts held at 10.5 to 13.5 °C was assessed by measuring T/S ratios (tissue radioactivity/serum radioactivity) from 1 hour to 10 days after intraperitoneal injection of L-thyroxine– 125 I.T/S ratios were highest for gall bladder, liver, and gut, indicating a biliary thyroxine excretion route. Somewhat less uptake occurred in spleen, kidney, and gill. T/S ratios were lower still for skin and muscle but the pattern of T/S change with time suggested some radiothyroxine uptake by these tissues. Little uptake occurred in brain where low T/S ratios were consistently found.For most tissues there was no difference in thyroxine uptake between parr, smolts, and presmolts. However, for presmolts the means of gill T/S ratios were much higher than those for parr or smolts while the biliary thyroxine excretion route was most prominent in parr.The biological half-life of serum radioactivity after intraperitoneal injection of L-thyroxine– 125 I was similar for parr, presmolt, and smolt. Most of the serum radioactivity was not protein-bound and was probably free radiothyroxine. The injected radiothyroxine may have so increased the serum free thyroxine pool that serum protein thyroxine-binding sites were saturated.