Effects of Prazosin on Plasma Noradrenaline and Plasma Renin Concentrations in Hypertensive Subjects

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Abstract
The purpose of the present study was to investigate whether a fall in vascular resistance produced by prazosin would affect adrenergic control of blood pressure and whether the hypotensive effect would be related to pretreatment parameters of sympathetic function. In 28 patients with uncomplicated essential hypertension, prazosin lowered systemic and renal vascular resistance without any change in cardiac output, renal blood flow, or blood volume. While noradrenaline levels rose significantly, plasma renin concentrations remained unchanged and aldosterone levels fell. In 15 of the patients, sympathetic function was assessed by measuring changes in blood pressure, heart rate, noradrenaline, and renin during two stimulation models (isometric exercise and exposure to noise). While the profile of changes was not modified by prazosin, it appeared that pretreatment responsiveness could fairly well predict the hypotensive response to subsequent therapy with prazosin. It is concluded that the hypotensive effect of prazosin is related to sympathetic responsiveness during stimulation and that this responsiveness in itself is not appreciably affected by this drug.

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