Subnormal growth hormone responses to acutely administered dexamethasone in depression

Abstract

Acute oral administration of dexamethasone (DEX) stimulates growth hormone (GH) release at 3 hours in normal controls and provides us with a novel probe with which to study the somatotrophic axis. In affective illness GH release is subnormal in response to a number of stimuli. We decided to investigate the acute effects of DEX-induced GH release in depression. A between subjects parallel group design was employed. Baseline levels of GH and cortisol were taken after which 4 mg of oral DEX was administered. Plasma samples for GH estimation were taken at +60, +180, +240 and +300 minutes. Sixteen normal subjects and 16 unipolar, nonpsychotic, melancholic DSM-111R major depressives were studied. Depressed subjects had to score over 17 on the Hamilton Depression Rating Scale; the mean +/- SEM scores were 27.4 +/- 1.0. Plasma GH and cortisol levels were measured by radioimmunoassay. Baseline mean +/- SEM GH levels (depressives 2.4 +/- 0.6 mU/l; controls 2.6 +/- 0.4 mU/l) did not differ significantly between the two groups (P < 0.28). DEX-induced GH secretion was subnormal in depressives as opposed to controls (2.1 +/- 0.7 vs 19.4 +/- 2.2 mU/l, P < 0.001). There were significant differences between the two groups at 60, 180 and 240 minutes (P < 0.05). Baseline cortisol values were significantly different between the two groups (depressives 303.3 +/- 31.5 nmol/l; controls 138 +/- 4.7 nmol/l). An analysis of covariance, with cortisol as a covariate, still found the depressives to have significantly subnormal GH responses as compared to the control group (P < 0.05). Dexamethasone-induced GH release is subnormal in depression.