alpha 2-Adrenergic receptor sensitivity in depression. The plasma MHPG, behavioral, and cardiovascular responses to yohimbine.

alpha 2-Adrenergic receptors play a major role in the regulation of the noradrenergic system. To assess the function of these receptors relative to possible abnormalities in noradrenergic function in depression, responses to the alpha 2-antagonist yohimbine hydrochloride were investigated in 45 depressed patients and 20 healthy control subjects. Plasma 3-methoxy-4-hydroxyphenylglycol (MHPG), blood pressure (BP), pulse, subjective mood, and somatic symptoms were measured before and during yohimbine and placebo administration. The 25% increase in plasma MHPG levels produced by yohimbine did not differ between patients and controls. Mood responses also tended to be similar between groups, with patients reporting only minor improvement in depression following yohimbine. However, yohimbine caused significantly greater increases in somatic symptoms and tended to produce a greater increase in BP in patients than in controls. Evaluation of patient subgroups divided by the presence or absence of melancholia, psychosis, prominent anxiety, or personality disorder did not demonstrate consistent differences. In contrast, comparison of these findings with a prior study showed that patients with panic disorder and agoraphobia who received yohimbine manifested significantly greater increases in MHPG levels and ratings of anxiety, nervousness, and depression than depressed patients. These findings suggest that patients with major depression do not demonstrate marked abnormalities in alpha 2-adrenergic autoreceptor function.