Cellular sodium transport via the Na+, K+-ATPase contributes significantly to daily energy expenditure. The effect of a meal on leucocyte Na+ transport and intracellular electrolytes was therefore investigated in lean normal subjects at room temperatures of 23° and 33°, to determine if the Na pump responds to the need for thermogenesis. In the fasting state, the ouabain-sensitive efflux rate which reflects active Na+ transport, and the intracellular electrolytes were similar. At 2 h after eating a 4·2 MJ (1000 kcal) meal, the ouabain-sensitive efflux rate constant rose when the room temperature was 23° but not at 33°. The ouabain-sensitive Na+ efflux rate, an index of active Na+ transport, 0rose post-prandially at 23° only. The post-prandial activation of leucocyte active Na efflux in normal subjects was blunted at higher environmental temperatures, when the need for thermogenesis was reduced.
