YOHIMBINE EFFECTS ON BLOOD-PRESSURE AND PLASMA-CATECHOLAMINES IN HUMAN HYPERTENSION

The purpose of this study has been to test the hypothesis of an alpha( 2)-adrenoreceptor alteration in human essential hypertension. The desi gn of the study involved the oral administration of 10 mg yohimbine, a n alpha(2)-adrenergic antagonist, to 25 healthy volunteers and 29 sex- and age-matched untreated hypertensive patients. Volunteers and patie nts were studied twice in random order, after placebo or yohimbine tre atment, in supine and upright positions. Arterial pressure and heart r ate were monitored by servoplethysmomanometry, and venous plasma catec holamines were determined by HPLC with electrochemical detection. Yohi mbine induced a significant increase in diastolic pressure only in the hypertensive patients. Plasma norepinephrine was increased significan tly in both yohimbine-treated groups, but the percent increase of plas ma norepinephrine after the standing test was decreased significantly only in the healthy yohimbine-treated subjects. Plasma dopamine was in creased significantly only in the healthy yohimbine-treated subjects. The response of plasma dopamine to the upright position was modified o nly in the healthy yohimbine-treated subjects. The decrease observed a fter 2 min of standing was abolished, showing the involvement of alpha (2)-adrenoreceptors in the physiologic response of plasma catecholamin es in healthy volunteers. Our data may be consistent with some in vivo evidence of an alpha(2)-adrenoreceptor desensitization or an alterati on in the balance of alpha-adrenoreceptors in human hypertension.