No major thermogenic role for (Na+ + K+)-dependent adenosine triphosphatase apparent in hepatocytes from hyperthyroid rats.

(Na+ + K+)-dependent ATPase activity, heat production and oxygen consumption were increased by 59%, 62% and 75% respectively in hepatocytes from tri-iodothyronine-treated rats. Ouabain at concentrations of 1 and 10 mM decreased oxygen uptake by 2--8% in hepatocytes from euthyroid rats and by 5--15% in hepatocytes from hyperthyroid animals. Heat output was decreased by 4--9% with the glycoside in isolated liver parenchymal cells from the control animals and by 11% in the cells from the tri-iodothyronine-treated animals. These results do not support the hypothesis that hepatic (Na+ + K+)-ATPase plays a major role in increased heat production in hepatocytes from hyperthyroid rats.