Blood pressure, plasma volume, and catecholamine levels during enalapril therapy in blacks with hypertension

Abstract

The effect of enalapril, an antihypertensive inhibitor of angiotensin-converting enzyme, on plasma catecholamine levels and plasma volume (PV) has not been well established. In a randomized, double-blind study, 29 subjects (28 blacks and one white) received one of the following dosing regimens: hydrochlorothiazide (HCTZ), 25 mg twice a day (group 1; n = 12); enalapril, 10 mg twice a day (group 2; n = 12); or enalapril, 10 mg twice a day, with HCTZ, 25 mg twice a day (group 3; n = 5). Dosages were doubled after 4 wk if diastolic blood pressure was greater than or equal to 90 mm Hg. After 8 wk of therapy, supine blood pressure decreased by 24.1/16.0 mm Hg (systolic/diastolic) in group 1, by 10.8/4.0 mm Hg in group 2, and by 48.0/27.8 mm Hg in group 3. Mean values of supine plasma levels of norepinephrine, epinephrine, and dopamine did not change with therapy. PV fell 7.9% in group 1, 1.3% in group 2, and 5.0% in group 3. There were no correlations between changes in PV and blood pressure, but a decrease in PV correlated with an increase in plasma norepinephrine levels in the group treated with HCTZ alone (r = -0.65) and in all 29 subjects combined (r = -0.45). Enalapril alone was not very effective in lowering blood pressure in these subjects, but the combination of enalapril with HCTZ was very effective. There was no evidence of a direct effect of enalapril on the sympathetic nervous system or on PV.

Absence of a pharmacokinetic interaction between enalapril and frusemide.

“…Diuretics, by reducing the extracellular volume, lead to an increase in the activity of the renin-angiotensin-aldosterone system. The combined use of diuretics and converting enzyme inhibitors in the treatment of hypertension can therefore be envisaged and has been shown to be efficacious in clinical practice (Ferguson et al, 1982;Freier et al, 1984;Gomez et al, 1984;Lewis et al, 1985). The aim of this study was to determine if a pharmacokinetic interaction occurs between enalapril and frusemide.…”