Factors influencing the affinity and capacity of T3-binding sites in hepatic nuclei of rainbow trout,Oncorhynchus mykiss

✍ Scribed by Bres, O. ;Cyr, D. G. ;Eales, J. G.

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 765 KB
• Volume: 254
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402540110

✦ Synopsis

Abstract

The effects of several variables were tested on the in vitro binding affinity (K~a~) and maximum binding capacity (MBC) of saturable 3,5,3′‐triiodo‐L‐thyronine (T~3~)‐binding sites (putative thyroid hormone receptors) extracted from hepatic nuclei of immature rainbow trout held on a 12L:12D photocycle at 12°C. Neither K~a~ nor MBC varied during the daily photocycle, nor were they influenced by the growth rate, food ration, or a 13‐fold chronic elevation in plasma T~3~. However, MBC was inversely correlated with fish size and was depressed significantly by two injections of 17β‐estradiol (E~2~) or starvation for 3 or 12 days. The K~a~ was uninfluenced in either case. Since both E~2~ and starvation also depress T~3~ levels in the blood, the decrease in MBC could be secondary to this change. The drug ipodate, which depresses plasma T~3~, also lowered the MBC. However, MBC remained low in ipodate‐treated trout given exogenous T~3~, thus suggesting that the effect of ipodate was not due to T~3~ deprivation. It remains to be shown, therefore, that plasma T~3~ depression itself can modify MBC. It is concluded that increasing body size and catabolic states, both of which are associated with a decrease in specific growth rate, tend to decrease the abundance of hepatic T~3~ receptors.