Relationship between change in erythrocyte sodium and antihypertensive response to enalapril

Abstract

To investigate the effects of enalapril and hydrochlorothiazide on erythrocyte sodium and potassium in relation to their effects on BP, 28 men (mean age 46 years, range 22-64 years) with previously untreated essential hypertension (casual DBP > or = 95 mmHg) were randomised to enalapril (n = 14) or hydrochlorothiazide (n = 14) treatment. BP was also measured intraarterially (brachial artery) and the mean arterial pressure (MAP) recorded. Intraerythrocyte sodium and potassium were measured by flame photometry at baseline and after 26 weeks of active treatment in the hypertensive patients and also in 28 age- and sex-matched normotensive control subjects. There was a significant positive relationship between intra-arterial BP and intraerythrocyte sodium in untreated hypertensives, but there was no significant difference in mean intraerythrocyte sodium or potassium content between hypertensive and normotensive subjects at baseline. The distribution of values of intraerythrocyte sodium, however, differed between hypertensive and normotensive subjects. Supine MAP was lowered from 113 +/- 4 to 97 +/- 3 mmHg and from 110 +/- 3 to 102 +/- 2 mmHg on enalapril and hydrochlorothiazide treatment, respectively. BP reduction with enalapril was associated with a significant decrease in intraerythrocyte sodium (P = 0.02), while hydrochlorothiazide had no effect. There was no significant correlation between delta MAP and delta intraerythrocyte sodium after 26 weeks in any of the groups. Intraerythrocyte potassium did not change on treatment with either drug. In conclusion, there wa a significant relationship between intra-arterial BP and intraerythrocyte sodium in untreated hypertensives. Both enalapril and hydrochlorothiazide reduced BP effectively while enalapril only reduced intraerythrocyte sodium.(ABSTRACT TRUNCATED AT 250 WORDS)