Objective: Ghrelin stimulates growth hormone (GH) secretion both in vivo and in vitro. Ghrelin is mainly produced in and released from the stomach but it is probably also produced in the hypothalamic arcuate nucleus. Whether pituitary GH release is under the control of ghrelin from the stomach and/or from the arcuate nucleus is not known. Moreover, no data on the feedback of GH on systemic ghrelin concentrations are available. It has recently been suggested that ghrelin may induce obesity.
Design: In this study, we addressed the following two questions: a) are circulating ghrelin levels increased in human GH deficiency (GHD), and b) does GH treatment modify ghrelin levels in human GHD?
Methods: The study group consisted of 23 patients with GHD. Eighteen had developed adult-onset GHD and five had developed GHD in their childhood (childhood-onset GHD). Ghrelin was measured with a commercially available radioimmunoassay. All measurements were performed twice, first at baseline, before the start of GH replacement therapy, and then again after one year of therapy. GH doses were adjusted every 3 months, targeting serum total IGF-I levels within the normal gender- and age-related reference values for the healthy population. Maintenance doses were continued once the target serum total IGF-I levels were reached.
Results: The sum of skinfolds and body water increased significantly, body fat mass and percentage body fat decreased significantly and body mass index and waist-hip ratio were not significantly changed by one year of GH replacement therapy. Before the start of GH replacement therapy, mean value and range for fasting ghrelin in the studied GHD subjects tended to be lower in comparison with healthy subjects in the control group although the difference did not reach significance (GHD ghrelin mean 67.8 pmol/l, range 37.6-116.3 pmol/l; control mean 83.8 pmol/l, range 35.4-132 pmol/l; P=0.11). One year of GH replacement therapy did not modify circulating ghrelin levels (ghrelin before GH therapy: 67.8 pmol/l, range 37.6-116.3 pmol/l; after GH therapy: 65.3 pmol/l, range 35.8-112.6; P=0.56).
Conclusions: We did not observe elevated ghrelin levels in adult GHD subjects and GH replacement therapy did not modify circulating ghrelin levels, despite significant decreases in body fat mass and percentage body fat. It is conceivable that the lack of ghrelin modifications after long-term GH therapy was due to the reduction of adiposity and insulin on one hand, and increased GH secretion on the other. However, it is still possible that systemic ghrelin is involved in the development of obesity, both in normal and GHD subjects.