Guanfacine in essential hypertension: effect on blood pressure, plasma noradrenaline concentration and plasma renin activity.

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Abstract
1. The acute and chronic effects of guanfacine on blood pressure, plasma noradrenaline concentration and plasma renin activity were investigated in 23 patients (15 males, 8 females) with essential hypertension (WHO grade I-II). 2. Guanfacine induced a decrease in plasma noradrenaline concentration and plasma renin activity concomitant with a fall in blood pressure and heart rate in both the acute and the chronic study. 3. The adrenergic response to upright posture, reflected by an increase in plasma noradrenaline concentration and plasma renin activity, was not abolished after chronic guanfacine therapy. 4. The decrease in blood pressure 15 min after intravenous administration of guanfacine was inversely correlated with the basal sympathetic activity before treatment and with the decrease in plasma noradrenaline. 5. After chronic treatment with guanfacine no significant correlation existed between blood pressure reduction and the concomitant changes in peripheral sympathetic and/or plasma renin activity. 6. Despite the lack of a close correlation it is suggested that the antihypertensive effect of guanfacine in patients with essential hypertension is at least partially mediated by an inhibition of the sympathetic nervous and plasma renin activity.