Nonlinear relationship between erythrocyte sodium-lithium countertransport and blood pressure in man.

A relationship between erythrocyte Na+/Li(+)-countertransport activity and blood pressure was studied in a randomly selected sample (95 subjects) with full range of blood pressure, from a representative group of inhabitants of one of Moscow's districts. The mean rate of erythrocyte Na+/Li(+)- countertransport activity was higher (p < 0.01 or less) in the groups of subjects with both borderline (BH) and moderate essential hypertension (EH) as compared with the group of normotensives (NT). A positive correlation was found between the erythrocyte Na+/Li(+)- countertransport rate and age and body weight in the entire selected group. The total contribution of these confounding parameters is responsible for 20.4% of the interindividual variability of the Na+/Li(+)- countertransport activity. The individual Na+/Li(+)- countertransport values remained unchanged during at least 2 years of follow-up. A nonlinear relationship between erythrocyte Na+/Li(+)- countertransport activity and blood pressure was established in the entire group. No significant association between blood pressure and Na+/Li(+)- countertransport was seen at high and low values of these two parameters. A pronounced change in the erythrocyte Na+/Li(+)- countertransport values occurred within a narrow borderline blood pressure range.