Growth hormone (GH) responses to GH-releasing hormone in depression: correlation with GH release following clonidine

Twenty subjects (10 patients with major depressive disorder and 10 controls matched for age, gender, and ovarian status) received 1 microgram/kg synthetic human growth hormone-releasing hormone (GHRH)-44 amide as an i.v. bolus dose. Compared to controls, depressed patients showed a significant attenuation of net growth hormone (GH) responses to GHRH associated with normal basal GH concentrations. The blunted GH responses occurred in the face of significantly higher somatomedin C (Sm-C) concentrations. Comparison of GH responses after GHRH with GH output following the alpha 2-agonist clonidine (CLON) revealed a significant positive correlation. The concordance between GH responses after specific challenges at different levels of the GHRH-GH-somatomedin axis indicates the integrity of the hypothalamic-pituitary-somatotropic system in depression and supports the view that altered GH secretory patterns in depression may primarily be due to a suprapituitary disturbance.