Alpha 1- and alpha 2-adrenoceptor mediated vasoconstriction in the forearm: differences between normotensive and hypertensive subjects.

Alpha 1- and alpha 2-adrenoceptor mediated vasoconstriction were compared between 13 patients with essential hypertension and 13 normotensive controls, matched for age and sex. For this purpose changes in forearm blood flow induced by infusion of the selective alpha 1-adrenoceptor agonist methoxamine, the selective alpha 2-adrenoceptor agonist B-HT 933, the catecholamines adrenaline and noradrenaline and the alpha 2-adrenoceptor antagonist yohimbine were measured in both study groups. The catecholamines were infused together with propranolol to avoid beta-adrenergic effects. Forearm blood flow was measured by plethysmography. All agonists produced a dose-dependent vasoconstriction which was more pronounced in the hypertensive subjects but no preference was found for either the alpha 1- or alpha 2-adrenoceptor mediated vasoconstriction. Yohimbine induced a greater vasodilatation in the normotensive subjects. The greater vasoconstriction in the hypertensive patients could be explained by structural vascular changes. No evidence was found for an important role of alpha 2-adrenoceptor mediated vasoconstriction in essential hypertension.