Nuclear activation by thyroid hormone in liver of Singi fish: changes in different ion-specific adenosine triphosphatases activities

Various ion-dependent (Na+K+, Ca++ and Mg++) ATPases activities in liver cell nuclear membrane have been determined after a single injection of different doses (0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2 and 4 micrograms/g) of L-triiodothyronine (T3) in Singi fish, Heteropneustes fossilis Bloch. Administration of T3 at a minimum effective dose of 0.05 micrograms upto 4 micrograms/g induced a rise (14 to 43% over control value) in the Na+K+-ATPase activity in a dose-dependent fashion maximum upto 1 microgram/g dose, whereas Ca++-ATPase showed a dose-dependent increase (20 to 43% over control) with 0.25-1 microgram/g of T3, although the increase in the respective enzyme activity was maintained upto 4 micrograms/g of T3 dose. Mg++-ATPase activity in liver cell nuclear membrane was found to be increased at 1 microgram-4 micrograms/g of T3 dose, showing a similar magnitude of increase (7% over the control value) with these doses of T3. Other doses of T3 (0.01 and 0.025 micrograms/g) were ineffective in altering the different ion-specific ATPase activity. Treatment of Singi fish with thiourea (1 mg/ml) for 30 days caused a significant fall in Na+K+, Ca++ and Mg++-ATPase activities upto 21%, 17% and 5%, respectively, below the euthyroid control level. A single injection of T3 at the dose of 1 microgram/g in the hypothyroid fish raised the Na+K+ and Ca++-ATPase activities to about 36% over the control value, and the Mg++-ATPase activity was restored to only the control level. Thus a dose-dependent nuclear effect of T3 is evident from the present investigation.