Objective: Human obesity is characterized by growth hormone (GH) deficiency, which appears primarily related to a central pattern of obesity and is reverted on weight loss. As yet, the metabolic basis of the GH deficiency remains to be elucidated. The recently discovered endogenous ligand for the GH secretagogue receptor, ghrelin, stimulates GH secretion when administered to rodents or healthy humans. It may thus be hypothesized that low ghrelin levels underlie the hyposomatropism in obesity.
Research methods and procedures: We have tested this hypothesis in individuals with widely varying body mass and fat distribution and evaluated whether the improved GH concentrations on weight loss are associated with enhanced ghrelin levels.
Results: Both plasma GH and ghrelin levels were reciprocally related with body mass index (r = -0.67, p < 0.001). However, whereas 24-hour GH secretion was negatively related to the visceral fat area (r = -0.72, p < 0.01), ghrelin levels showed a positive relationship with the visceral fat area (r = 0.49, p < 0.02). Weight loss resulted in increased GH secretion (median 24-hour GH area under the curve: 1983 vs. 4024 mU/day before and after weight loss, respectively; p < 0.01) but did not affect ghrelin levels. No relationship could be found between GH and ghrelin plasma levels in obese subjects when comparing diurnal concentration profiles.
Discussion: We showed that plasma ghrelin and GH levels are both reciprocally related with body mass index, but no causative relationship could be demonstrated between low ghrelin levels and the hyposomatropism in human obesity.