The effect of 3,5,3'-triiodo-L-thyronine on gill Na+/K+-ATPase of rainbow trout Salmo gairdneri, in fresh water.

Gill and liver microsomal Na+/K+-adenosine triphosphatase (ATPase) activities and plasma levels of 3,5,3'-triiodo-L-thyronine (T3) were measured in rainbow trout (100-300 g) immersed in a freshwater solution of T3 for 6 or 7 days at 11 degrees C. Ambient T3 (1.25 or 2 micrograms T3/100 ml H2O) elevated plasma T3 within a physiologic range; an ambient concentration of 10 micrograms T3/100 ml produced supranormal plasma T3 levels. All T3 treatments depressed gill ATPase to a similar degree. Liver ATPase was lower than gill ATPase and was elevated by a physiologic T3 treatment.