ERYTHROCYTE NA-ATPASE ACTIVITY DOES NOT PREDICT THERAPEUTIC RESPONSE TO CALCIUM-ANTAGONISTS IN ESSENTIAL-HYPERTENSION(,K+)

We investigated whether pre- and posttreatment analysis of erythrocyte membrane Na+,K+-ATPase (EC 3.6.1.37) activity would be a useful marke r for screening hypertensive patients to determine who might benefit f rom treatment with calcium antagonists. Erythrocyte Na+,K+-ATPase acti vity and sodium and potassium (ENa, EK) contents were determined in co ntrols and in patients with untreated essential hypertension before an d after 4 weeks of treatment with nitrendipine. Na+,K+-ATPase activity was significantly (P < 0.0001) less in untreated hypertensive patient s (n = 15; 104.60 +/- 29.37 nmol of phosphate produced per milligram o f protein per hour) than in controls (n = 15, 171.87 +/- 34.42). After 4 weeks of nitrendipine treatment Na+,K+-ATPase activity was greater than in the pretreatment group: 158.13 +/- 26.80 (P < 0.001). Pretreat ment ENa contents (22.34 +/- 4.77 mmol/L) were significantly (P < 0.00 01) higher than in the normotensive group (13.14 +/- 3.32 mmol/L), but there was no significant difference between the controls and the post treatment group (14.84 +/- 3.49 mmol/L). The control and pretreatment groups showed negative correlations between enzyme activity and systol ic/diastolic blood pressure (P < 0.0001). The control and the posttrea tment groups showed an inverse correlation between enzyme activity and ENa contents: r = -0.608 (P < 0.05) and r = -0.724 (P < 0.001), respe ctively. Although Na+,K+-ATPase is restored in hypertensive patients r eceiving nitrendipine treatment, relative changes in enzyme activity i n relation to relative reduction in blood pressure response to treatme nt were not correlated.