Adrenergic Receptor Sensitivity in Depression

Several recent investigations have raised the possibility that the sensitivity of alpha 2-adrenergic receptor may be of etiologic importance in depression. To assess whether abnormalities in presynaptic alpha 2-adrenergic receptor exist in depressed patients not taking drugs, the effects of an alpha 2 agonist, clonidine, on plasma 3-methoxy-4-hydroxyphenelethyleneglycol (MHPG) and on blood pressure (BP) were evaluated in 15 depressed patients and 12 healthy controls of similar age. The ability of clonidine to increase growth hormone (GH) secretion was also assessed. The effect of clonidine on plasma MHPG and BP was not different between the depressed patients and controls. However, the GH response to clonidine was blunted in the depressed patients. These results suggest that in depression (1) the sensitivity of the presynaptic alpha 2-adrenergic receptor is not abnormal, and (2) the sensitivity of postsynaptic adrenergic receptors may be decreased.