Growth hormone (GH) and prolactin responses after GH-releasing hormone in major depressive disorder: relationship to somatomedin C levels and dexamethasone suppressibility of cortisol

To explore the growth hormone-releasing hormone (GHRH)-GH-somatomedin axis in major depressive disorder, 12 patients and 12 normal controls matched to the patients on age, sex, ovarian status and body weight received synthetic human GHRH-44 amide (1 microgram/kg) as an intravenous bolus. Compared to controls, the depressed patients showed a reduction in baseline plasma GH and a significant attenuation of net plasma GH responses to GHRH. The blunted GH responses occurred along with significantly increased somatomedin C (Sm-C) concentrations. The impairment of GH responses to GHRH and the increased Sm-C concentrations in patients with depression could have resulted from episodic hypersecretion of GH during the daytime, indicating integrity of the negative feedback circuitry. Normal feedback regulation suggests that diurnal episodic hypersecretion of GH reflects an abnormality at or above the level of the hypothalamus, so that the GHRH-GH-somatomedin axis hyperactivity observed in certain patients with major depressive disorder may be due, at least in part, to hypersecretion of hypothalamic GHRH. Our failure to demonstrate a difference in plasma prolactin (PRL) responses to GHRH between controls and depressed patients indicates that GHRH is not a PRL releaser in patients with major depression and that the altered GH secretory dynamics may not be directly related to the altered circadian PRL secretion linked to depression.

Growth hormone (GH) response to GH-releasing hormone in depression

To explore the GHRH-GH-somatomedin axis integrity in major depressive disorder, 11 drug-free patients and normal subjects matched for age, sex, ovarian status, and body weight received 1 microgram/kg synthetic human GHRH-44 amide as an iv bolus dose. Compared to the normal subjects, the depressed patients had reduced mean basal serum GH levels [2.2 +/- 0.5 (+/- SE) vs. 1.1 +/- 0.2 ng/mL (micrograms/L); P less than 0.05] and a significant attenuation of the net GH response to GHRH [1346 +/- 499 vs. 217 +/- 46 ng.min/mL (micrograms.min/L); P less than 0.01]. The blunted GH responses occurred in the face of significantly increased plasma somatomedin C (Sm-C) levels [1.1 +/- 0.2 vs. 0.6 +/- 0.1 U/mL; P less than 0.05]. The magnitude of GH responses to GHRH did not differ between men and women and was not significantly correlated with age, body weight, baseline serum GH levels, or plasma Sm-C levels in either individual groups or both groups combined. The increased plasma Sm-C levels in the depressed patients could have resulted from diurnal hypersecretion of GH, and the diminished GH responses to GHRH may reflect normal Sm-C-mediated feedback at the level of the pituitary. The presumed GH hypersecretion may be due to decreased hypothalamic somatostatin release and/or hyperactivity of GHRH-containing neurons. Thus, the pathological process resulting in abnormal GH secretory patterns associated with depression may occur primarily at a suprapituitary site.