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It has been suggested that there are altered levels of norepinephrine or other neurotransmitters at functionally important receptors in patients with depressive disorders. This hypothesis is difficult to study in the human central nervous system. However, noradrenergic function can be assessed indirectly with peripheral-blood lymphocytes used as a model of the beta-adrenergic receptor complex. We found that drug-free inpatients with endogenous depression had lower isoproterenol-stimulated cyclic AMP levels in intact lymphocytes than did healthy control subjects (3.9 +/- 0.5 vs. 7.4 +/- 1.0 pmol per 10(6) cells, P less than 0.01). The density and affinity of beta-adrenergic receptors were similar in controls and depressed subjects (beta-receptor number, 5.4 +/- 0.7 and 5.3 +/- 0.8 fmol per 10(6) cells; binding affinity, 106 +/- 7.6 vs. 99.2 +/- 11.4 pM, respectively). When the depressed patients were subdivided by psychomotor manifestations, binding characteristics were indistinguishable among the subgroups. However, a significant reduction in beta-adrenergic responsiveness was observed in patients with psychomotor agitation, as compared with controls (2.6 +/- 0.5 vs. 7.4 +/- 1.0 pmol per 10(6) cells, P less than 0.01), but not in patients with psychomotor retardation (5.8 +/- 1.1 pmol per 10(6) cells, P less than 0.05). Thus, the desensitization of beta-adrenergic receptors was correlated more closely with the severity of psychomotor agitation than with the overall severity of depression.
Mann et al. (Thu,) studied this question.