Changes in haemodynamics and body fluid volume due to enalapril in patients with essential hypertension on chronic diuretic therapy.

In 12 patients with essential hypertension who remained hypertensive despite chronic chlorthalidone treatment, the effect of 2 weeks of additional therapy with the converting enzyme inhibitor (CEI) enalapril on blood pressure and body fluid volumes has been evaluated. The objective was to examine the influence of a diuretic-stimulated renin-angiotensin-aldosterone system (RAAS) on haemodynamics and body fluid volume. Mean arterial pressure (MAP -21%), total peripheral resistance index (TPRI -22%) and plasma aldosterone concentration (PAC -39%) were decreased, and plasma renin activity (PRA 660%) was increased. The average heart rate (HR), cardiac index (CI), plasma volume (PV), blood volume (BV), extracellular fluid volume (ECFV) and body weight (BW) remained unchanged. A negative correlation was found between the per cent changes in ECFV and PAC. Thus, body fluid volumes during chronic diuretic treatment are well preserved even when the RAAS with its sodium retaining properties is suppressed by CEI. Possible mechanisms are a volume (not angiotensin II) - dependent stimulation of aldosterone and a fall in blood pressure.