INHIBITION OF NA-K+-ATPASE BY DIGOXIN AND ITS RELATION WITH ENERGY-EXPENDITURE AND NUTRIENT OXIDATION RATE()

This study investigates the effects of digoxin, an inhibitor of the Na f pump (Na+-K+-ATPase), on resting metabolic rate (RMR), respiratory q uotient (Rand), and nutrient oxidation rate. Twelve healthy male subje cts followed a double-blind protocol design and received either 1 mg/d ay digoxin or a placebo 2 days before indirect calorimetry measurement s. Digoxin induced a 0.22 +/- 0.07 kJ/min or 3.8 +/- 1.5% (mean +/- SE , P = 0.01) decrease in RMR and a 0.40 +/- 0.13 kJ/min (P = 0.01) decr ease in fat oxidation rate, whereas carbohydrate and protein oxidation rates did not change significantly. A dose-response relationship betw een serum digoxin and RQ was observed. These results suggest that digo xin reduces not only RMR but also fat oxidation rate by mechanisms tha t remain to be elucidated. Because a linkage and an association betwee n genes coding the Na+-K+-ATPase and the RQ have been previously obser ved, the present demonstration of an effect of Na+-K+-ATPase inhibitio n on fat oxidation rate strengthens the concept that the activity of t his enzyme may play a role in body weight regulation.