Leukocyte isotopically exchangeable intracellular sodium fractions in lean and overweight hypertensives

Leukocyte intracellular sodium, as measured by flame photometry, is increased in essential hypertension, especially when associated with a body mass index greater than 27 kg · m^-2. A triple isotope method for measuring the isotopically exchangeable pool of intracellular sodium was used to assess if this pool was increased in hypertension. No significant differences in the isotopically exchangeable intracellular sodium concentration were found between lean and overweight hypertensives compared with normotensive controls. Lean hypertensives with systolic blood pressures below the median had significantly lower exchangeable intracellular sodium concentrations than lean normotensives, whereas those with systolic blood pressures above the median had raised exchangeable intracellular sodium concentrations. The obese hypertensives did not show this trend. The exchangeable intracellular sodium concentration was correlated to systolic (r = .53, P < .001) and diastolic (r = 0.39, P < .01) blood pressure in hypertensives. We conclude that the increase in total cellular sodium content (as measured by flame photometry) in hypertensives described in previous studies is not associated with any increase in the isotopically exchangeable pool of intracellular Na⁺, except in those lean hypertensives with systolic blood pressures above the median. By implication, there may be an increased slowly exchangeable pool of intracellular Na⁺ in leukocytes from most hypertensives.