Yohimbine effects on blood pressure and plasma catecholamines in human hypertension

The purpose of this study has been to test the hypothesis of an α2-adrenoreceptor alteration in human essential hypertension. The design of the study involved the oral administration of 10 mg yohimbine, an α2-adrenergic antagonist, to 25 healthy volunteers and 29 sex- and age-matched untreated hypertensive patients. Volunteers and patients were studied twice in random order, after placebo or yohimbine treatment, in supine and upright positions. Arterial pressure and heart rate were monitored by servoplethysmomanometry, and venous plasma catecholamines were determined by HPLC with electrochemical detection. Yohimbine induced a significant increase in diastolic pressure only in the hypertensive patients. Plasma norepinephrine was increased significantly in both yohimbine-treated groups, but the percent increase of plasma norepinephrine after the standing test was decreased significantly only in the healthy yohimbine-treated subjects. Plasma dopamine was increased significantly only in the healthy yohimbine-treated subjects. The response of plasma dopamine to the upright position was modified only in the healthy yohimbine-treated subjects. The decrease observed after 2 min of standing was abolished, showing the involvement of α2-adrenoreceptors in the physiologic response of plasma catecholamines in healthy volunteers. Our data may be consistent with some in vivo evidence of an α2-adrenoreceptor desensitization or an alteration in the balance of α-adrenoreceptors in human hypertension.