Growth hormone response to growth hormone-releasing hormone (GHRH), insulin, clonidine and arginine after GHRH pretreatment in obese children : evidence of somatostatin increase ?

To clarify the possible neuroendocrine mechanisms underlying the impairment in growth hormone (GH) secretion present in obesity, the GH response to GH-releasing hormone (GHRH, N = 6), insulin hypoglycemia (N = 6), clonidine (N = 7) and arginine (N = 8) after GHRH pretreatment (1 microgram/kg iv 2 h before the tests) was evaluated in 27 obese peripubertal children and in a group of normal-weight short-normal children (N = 26). Growth hormone-releasing hormone pretreatment and all further stimuli elicited a statistically significant GH response in both obese and short-normal children; in the latter group arginine did not induce a significant GH response. No differences were found among the GH responses after the second stimuli in obese children, while in short-normal children the arginine peak and area values were lower than after GHRH and clonidine. Comparison between the two groups showed similar baseline but higher stimulated GH levels in normal-weight children after all tests except arginine, after which no difference was present. In conclusion, the neuroregulation of GH release seems to be similar qualitatively in normal-weight and obese youngsters; the different behavior observed after arginine, which is supposed to act through somatostatin inhibition, might be due to a chronic increase in somatostatinergic tone responsible for the lower stimulated GH levels in obesity.