[Sodium and potassium in children with hypertension]

On a baseline survey of 4936 school children, age ranged from 6 to 16 years, 199 children with the systolic blood pressure (SBP) value equal or greater than 95-th percentiles for age and sex were chosen as the hypertensive group (HBP), and the same number of children with the SBP lower than 50-th percentiles were matched as the normotensive group (NBP). For both groups the intra-RBC and plasma Na and K content, three sequential nights 8-hour urinary Na, K and creatinine excretion, and an oral saline-load test were performed. The results show that: (1) The intra-RBC K in the HBP was lower than in NBP, 259 +/- 57 vs 291 +/- 78 mumol/g-protein, P less than 0.01. That in those with positive hypertensive family history (FH+) was lower than in those of negatives (FH-). The intra-RBC K content was correlated inversely with diastolic BP, r = -0.43, P less than 0.001. No correlation between intra-RBC Na and BP was found; (2) Plasma Na concentration in HBP was much lower than in NBP, 137.5 +/- 7.9 vs 142.6 +/- 6.9 mmol/L, P less than 0.001. No difference was found between FH+ and FH-; (3) Mean 8-hour urinary K excretion at night was lower in HBP than in NBP, 23.9 +/- 11.5 vs. 28.2 +/- 14.7 mmol/g-creatinine, P less than 0.01; (4) After a load of oral saline the 4-hour urinary Na excretion was significantly higher in HBP than in NBP, 39.5 +/- 29.1 vs 30.8 +/- 23.2 mmol, P less than 0.01. Of those children with FH-, the 4-hour Na excretion in HBP was higher than in NBP, 39.8 +/- 29.4 vs 29.3 +/- 21.5 mmol, P less than 0.001, but no significant difference was found between HBP and NBP in children with FH+. We believed that the above changes in electrolytes in the children with their BP at higher-level percentiles represent an abnormal relation between potassium and arterial BP in the early stage of hypertension, as well as the early compensatory natriuresis of the kidneys.