Effect of diet upon the erythrocyte Na,K pump.

The number of erythrocyte Na,K-ATPase pump units has been found to be reduced in some populations of obese humans, but the effect of dietary factors upon the status of the erythrocyte pump has not been delineated. We have measured the number of Na,K-ATPase pump units by [3H]ouabain binding and the activity of the pump by ouabain-inhibitable 86rubidium uptake in response to nutritional maneuvers in several patient groups. There was no consistent change in the number or activity of Na,K-ATPase units in response to 1) an acute 600-cal meal, 2) a 3-day fast or refeeding after a fast in normal weight or obese subjects, 3) 2 weeks of hypocaloric (600 cal) feeding in obese subjects. Individuals with anorexia nervosa were also not significantly different from age- and sex-matched control subjects with respect to the erythrocyte Na,K pump. It is concluded that the circulating erythrocyte does not regulate the number or activity of Na,K pump units in response to short or medium term nutritional maneuvers. Differences between obese and thin populations with respect to the Na,K pump are not likely to be secondary to nutritional differences between the two groups.