Elevated plasma concentrations of alpha 1-acid glycoprotein, a putative endogenous inhibitor of the tritiated imipramine binding site, in depressed patients.

The plasma concentration of alpha 1-acid glycoprotein, a putative endogenous inhibitor of the site labeled by tritiated imipramine, was measured by a radial immunodiffusion assay in 36 normal human volunteers and 51 drug-free patients who fulfilled DSM-III criteria for major depression. The depressed patients exhibited a significant elevation in the plasma concentration (+/- SEM) of alpha 1-acid glycoprotein (79.6 +/- 4 mg/dL) when compared with the age- and sex-matched controls (61.7 +/- 3 mg/dL). Fourteen of the 51 patients with major depression had plasma alpha 1-acid glycoprotein concentrations that were higher than the highest values of the normal controls. There was no relationship between plasma alpha 1-acid glycoprotein concentrations and sex or affinity of platelet tritiated imipramine binding of either the normal volunteers or the depressed patients. In the depressed patients, there was a significant positive correlation between plasma concentrations of alpha 1-acid glycoprotein and postdexamethasone plasma cortisol concentrations, and two measures of depression severity, the Montgomery-Asberg Rating Scale for Depression and the Center for Epidemiologic Studies-Depression Scale, and a significant negative correlation with age. These data provide the first evidence of alterations of an endogenous inhibitor of the tritiated imipramine binding site/serotonin transporter in depressed patients.