ORAL YOHIMBINE INCREASES BLOOD-PRESSURE AND SYMPATHETIC NERVOUS OUTFLOW IN HYPERTENSIVE PATIENTS

Yohimbine is an alpha2-adrenoceptor antagonist that is FDA approved fo r treatment of impotence. The drug is an indolalkylamine alkaloid chem ically similar to reserpine and is believed to act through sympatholys is. We examined effects of oral yohimbine on blood pressure (BP) and p lasma levels of catechols in patients with essential hypertension, a c ondition in which most drug treatments can produce impotence. In 25 un medicated hypertensive subjects, vital signs were measured and blood s amples were obtained through an indwelling antecubital venous catheter at baseline and 1 and 2 h after subjects ingested 4 5.4-mg tablets of yohimbine. Mean blood pressure (MBP) increased by an average of 5 mm Hg (p < 0.01), plasma norepinephrine (NE) levels increased by 66% (p < 0.001), and plasma dihydroxyphenylglycol (DHPG) levels increased by 2 5% (p < 0.01) at 1 h after drug administration. The magnitude of the p ressor response was unrelated to baseline MBP but positively correlate d with the baseline NE level (r = 0.61, p < 0.01) and with the yohimbi ne-induced increment in plasma NE (r = 0.4, p < 0.01). The results ind icate that yohimbine does not inhibit and actually stimulates sympathe tically mediated NE release in humans and that the increased NE releas e produces a pressor response. Yohimbine should be administered with c aution to patients with high BP, especially in individuals with eviden ce for increased basal sympathetic outflow or those undergoing concurr ent treatment with tricyclic antidepressants or other drugs that inter fere with neuronal uptake or metabolism of NE.