Intra-erythrocytic sodium content in normotensive offspring of normotensive and hypertensive subjects: an epidemiological study.

An increase in intra-erythrocytic sodium (IENa) content has been proposed as a genetic marker of essential hypertension. Intra-erythrocytic sodium was studied using hypotonic lysis and flame photometry after four washings with isotonic MgCl2 in 240 normotensive subjects (aged 10-45 years) on a free diet with (F+, 121 patients) or without (F-, 119 patients) hypertensive parents, recruited from a random sample of the general population. Systolic blood pressure was significantly higher in males F+ than in males F- (130 +/- 2 versus 125 +/- 2 mmHg, mean +/- s.e.m., P < 0.05), while IENa did not differ. In contrast, intra-erythrocytic potassium content (IEK) was significantly lower and red cell sodium potassium (Na:K) ratio significantly higher in F+ than F-. This might reflect decreased NaK pump activity, or increased membrane permeability to cations which causes increased K leakage. No differences in blood pressure, IENa or IEK showed in female F+ versus F-. It is concluded that IENa is not a genetic marker of hypertension, and that it is probably influenced by exogenous factors. Being associated with differences in blood pressure, the abnormalities of IEK and Na:K ratio might be pathogenetically linked to an early increase in blood pressure.