Nuclear Activation by Thyroid Hormone in Liver of Singi Fish: Changes in Different Ion-Specific Adenosine Triphosphatases Activities

Summary

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 μg/g) of L-triiodothyronine (T₃) in Singi fish, Heteropneustes fossilis Bloch. Administration of T₃ at a minimum effective dose of 0.05 μg upto 4 μg/g induced a rise (14 to 43% over control value) in the Na⁺K⁺-ATPase activity in a dose-dependent fashion maximum upto 1 μg/g dose, whereas Ca⁺⁺-ATPase showed a dose-dependent increase (20 to 43% over control) with 0.25-1 μg/g of T₃, although the increase in the respective enzyme activity was maintained upto 4 μg/g of T₃ dose. Mg⁺⁺-ATPase activity in liver cell nuclear membrane was found to be increased at 1 μg-4 μg/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 μg/g) were ineffective in altering the different ion-specific ATPases activity.

Treatment of Singi fish with thiourea (1 mg/ml) for 30 days caused a significant fall in Na⁺K⁺, Ca⁺⁺ and Mg⁺⁺-ATPases activities upto 21%, 17% and 5%, respectively, below the euthyroid control level. A single injection of T₃ at the dose of 1 μg/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.

Key-Words

Nuclear Membrane ATPases - T₃ Action - Fish Liver Metabolism - Enzyme Induction by Hormone