Central and Renal Circulation, Renin and Aldosterone in Plasma during Prazosin Treatment in Essential Hypertension

The hemodynamic adaptation and the change in the renin‐aldosterone system during treatment with a new vasodilating drug, prazosin (Peripress®), were studied in 14 patients with essential hypertension before and after 2 and 4 months of treatment. The mean daily dose was 2 mg/day for the first 2 months and was increased individually up to 7.0 mg/day during the last 2 months in those patients whose mean arterial blood pressure (MAP) remained elevated. The reduction of MAP was mainly due to a decline in peripheral resistance, but also to a decrease in cardiac output in 4 of the patients. Effective renal plasma flow increased from 220 to 254 ml/min m 2 , probably as a result of a fall in vascular resistance in the kidneys. The plasma volume showed a small, transient increase after 2 months, from 19.0 to 20.0 ml/cm body height, whereas pulmonary plasma volume was unchanged, indicating a slight redistribution of plasma between the pulmonary and the systemic circulation. Body weight increased from 75.1 to 77.1 kg which, although a crude parameter, might indicate volume expansion. Plasma renin activity showed a small, transient increase after 2 months, from 0.46 to 0.65 nmol A 1 /I h, whereas plasma aldosterone concentration was unchanged, indicating that a volume expansion was not a result of a stimulated renin‐aldosterone system. The serum sodium and chloride concentrations fell from 142.7 to 140.2 mmol/l and from 105.9 to 103.1 mmol/***l, respectively.