1. Intracellular Na+ concentration [Na+]i and Na+ extrusion catalysed by sodium, potassium-activated adenosine triphosphatase (Na+, K+-pump) were evaluated in erythrocytes from 21 obese children and 20 normal weight- and age-matched controls.
2. Obese children showed a significantly decreased Vmax for Na+, K+-pump-mediated Na+ efflux (5638 ± 338 vs 7597 ±335 μmol h−1 litre−1 of cells mean±SEM, P = 0.01), while [Na+]i (9.3±0.3 vs 9.1 ± 0.5 mmol/litre of cells, mean±SEM, NS) and Na+ efflux in fresh cells (2380± 153 vs 2533 ± 180 μmol h−1 litre−1 of cells, mean ±sem, NS) were similar in both groups.
3. Mean diastolic blood pressure was significantly higher in obese children than in controls, although both groups were normotensive (73.8 ± 1.3 vs 66.2 ±1.9 mmHg, mean ± sem, P = 0.009).
4. Abnormal Na+, K+-pump activity is present in individuals with idiopathic obesity.
5. The possible link between obesity and blood pressure regulation may be mediated through modifications in Na+, K+-pump activity.