Response of hepatic thyroxine 5′-deiodinase of rainbow trout,Oncorhynchus mykiss, to chronic ingestion of 3,5,3′-triiodo-L-thyronine

✍ Scribed by Eales, J. G. ;Finnson, K. R.

• Book ID: 102894169
• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 620 KB
• Volume: 257
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402570213

✦ Synopsis

Rainbow trout held a t 65°C were fed food supplemented with 12 ppm T3 (3,5,3'triiodo-L-thyronine). By 2 weeks, plasma T3 had increased from 3.7 ng/ml (controls) to 12 ng/ml and stayed at that level for 12 weeks with minor change in plasma L-thyroxine (TJ. The hepatic microsomal 5'-deiodinase (5'-D) activity (Vmax) fell to 25% of control values by 2 weeks and by 12 weeks was undetectable. Trout were also fed the T3-supplemented food for 6 weeks and then reverted to control food (0 ppm T3) for 6 weeks. After 2 weeks reversion, plasma T3 was 48% lower and 5'-D V, , , 78% lower than for control fish fed 0 ppm T3 throughout; after 6 weeks reversion, plasma T3 had recovered, but 5'-D had regained only 58% of control values. These data confirm that exogenous T3 suppresses endogenous T3 production and suggest extrathyroidal autoregulation of T3 production. Furthermore, even 6 weeks after T, treatment had ceased, hepatic 5'-D was subnormal, indicating development of T3 dependency.