Depressive symptoms and the glucose tolerance test and insulin tolerance test

Patients with severe depression have been observed previously to have a reduced rate of glucose utilization accompanied by elevated serum insulin levels during the intravenous glucose tolerance test (GTT) and a reduced metabolic responsiveness to exogenous insulin during the insulin tolerance test (ITT). These abnormalities were less obvious in patients with neurotic depression as compared to patients with severe endogenous or "psychotic" depression. To evaluate more fully the relationships of depressive symptomatology to these metabolic abnormalities, patients were rated by nursing staff on a short clinical rating scale (SCRS) and by a psychiatrist on the Brief Psychiatric Rating Scale (BPRS) at the time the metabolic measurements were made. Patients were given the GTT and the ITT once when they were off medication and symptomatic and then again 3 to 8 weeks later when symptoms had decreased following amitriptyline treatment. Fasting serum-free fatty acid levels (FFA) had a significant positive correlation to rating of anxiety. Fasting levels of glucose, insulin, and human growth hormone (HGH) did not significantly correlate to any of the ratings. A decreased rate of glucose utilization (k) correlated significantly with increased ratings of motor retardation, emotional withdrawal, and blunt affects, but not to other depressive symptoms. The responsiveness of FFA and HGH during the ITT was significantly less in patients with more severe symptomatology; responsiveness improved when those patients improved. Neither incorrelated to the ratings. These data suggest that within the sydrome of depression, increased FFA is realated to anxiety, decreased glucose utilization is related to motor retardation, emotional withdrawal, and blunt affect, and that decreased FFA and HGH responsiveness to insulin is a nonspecific correlate of the general depressive syndrome.