The authors measured plasma 3-methoxy-4-hydroxyphenylglycol (MHPG),
plasma norepinephrine, blood pressure, and heart rate responses to the
alpha 2-adrenergic agonist clonidine in 25 depressed patients and 25 normal
control subjects. In the control subjects clonidine reduced plasma
norepinephrine, blood pressure, and heart rate significantly more than
placebo. In the depressed patients clonidine reduced blood pressure and the
percent fall in plasma norepinephrine but not plasma MHPG or heart rate
significantly more than placebo. The absolute and percent reductions in
plasma MHPG and heart rate following clonidine were significantly less than
in control subjects. These results raise the possibility that the
sensitivity of the alpha 2-adrenergic receptors inhibitory to noradrenergic
output may be reduced in depression.Abstract Teaser