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A total of 417 individuals from all four major sex-race groups were examined for the rate of sodium flux via the countertransport pathway and the sodium concentration within red cells. The age span was from early adolescence to retirement. Males of both races had sizable higher countertransport rates than did women (p less than 0.01), and a slight increase in sodium concentration (p greater than 0.05). Contrariwise, while whites or both sexes had higher countertransport than their black counterparts, sodium concentration was higher in blacks than whites (p less than 0.01). This pattern is not consistent with a direct relationship between both countertransport or sodium concentration and blood pressure which applies across both racial groups. Sex-race differences must be taken into account in any group comparisons of these variables.

Differences in red cell sodium content and sodium-lithium countertransport were studied in black and white children with a mean age of 12 years. For both boys and girls red cell sodium content was higher in blacks and countertransport lower (P less than 0.05). For both ethnic groups red cell sodium was lower in girls than boys and a consistent positive relationship was noted between body mass index and countertransport. Despite the lower red cell Na-Li countertransport values in black compared to white children, a significant positive correlation with systolic blood pressure was found independent of adiposity. In contrast, no correlation was evident between Na-Li countertransport and blood pressure in the white children. If red cell cation transport is confirmed as a marker for hypertension, study of racial differences may help explain the twofold higher prevalence of this disease among blacks.

A total of 448 individuals ranging in age from 11 to 72 years were studied in a series of seven population-based surveys. Although the relationship was positive in all surveys, a significant correlation was noted between sodium-lithium countertransport and blood pressure in only three of the seven. Hypertensives as a group had significantly higher levels of countertransport than did those with a normal blood pressure. In stepwise regression analysis, however, entering weight into the equation eliminated a significant predictive effect of countertransport. Red cell sodium concentration and membrane leak did not bear any significant relationship to blood pressure. The association between countertransport and blood pressure appears to be weaker in the general population than previously reported for case-control studies.

High school students who had at least one parent with hypertension (n = 22) were compared to schoolmates of the same age with a negative family history of hypertension in the parents (n = 21). We investigated in both groups the maximal rate of the ouabain-sensitive Na pump and the Na-K cotransport in nystatin-loaded cells and the Lii-Nao countertransport in lithium-loaded cells. The two groups were significantly different only in the sum of net Na transport mediated by the Na-K pump and Na-K cotransport. The mean diastolic blood pressure in the positive family history group was significantly higher. With control for blood pressure the difference in the maximal rate of Na transport was no longer significant; it remains uncertain if control for blood pressure represents "over-adjustment'. The finding of a higher maximal rate of Na transport in these adolescents who are at increased risk of future hypertension, yet currently well within the normal range, suggests that abnormal sodium metabolism may be a useful marker and appears early in the pathogenesis of this disease.

A randomized, crossover trial was carried out on the effect of moderate sodium reduction on red-blood-cell sodium metabolism. The participants were healthy high school students (mean age = 16 years, n = 33). Changes in sodium-lithium countertransport and intracellular sodium concentration were evaluated 24 days after a decrease in dietary sodium from approximately 110 to 40 mEq per day. Dietary sodium restriction had no significant effect on either sodium-lithium countertransport or intracellular sodium concentration.