Ghrelin, a novel GH-releasing n-octanoylated peptide, has been identified as an endogenous ligand for the 'orphan' GH secretagogue receptor. When administered iv or icv, Ghrelin causes a greater increase in serum GH concentrations than hexarelin or GHRH. However Ghrelin has a number of other actions: it promotes food intake, raises serum glucose and inhibits insulin secretion, increases ACTH and cortisol secretion and influences cardiac function.
In order to assess its physiological role in children, Ghrelin has been measured in serum samples from 277 children (Male 132, Female 145) aged 5 to 18 years, in which levels of the IGFs, IGF binding proteins 1 and 3 and leptin had been assayed. Ghrelin was measured by RIA (Phoenix, CA). It was detected in all samples with a mean value of 10.3ng/ml, range 0.01-49.3. Levels in males were slightly higher than in females (p=0.04). In the whole group, Ghrelin correlated negatively with age (rs=-0.19, p=0.002), but in each sex Ghrelin did not differ between the pre- and pubertal subjects. Additionally Ghrelin correlated negatively with IGF-I [rs=-0.24, p<0.001] (but not IGFBP-3), leptin (rs=-0.28, p<0.001] and height sds [rs=-0.13, p=0.03] (but not BMI sds), and positively with IGF-II [rs=+0.13, p=0.03] and IGFBP-1 [rs=+0.28, p<0.001]. In stepwise multiple regression, 10% of the variability in Ghrelin concentrations was accounted for by IGF-I (-, p=0.003) and leptin (-, p=0.019).
In this cross-sectional study, Ghrelin was present in the blood of all children. It is most significantly influenced negatively by serum IGF-I and leptin. If Ghrelin acts as a GH secretagogue, then IGF-I generated systemically may act as a feedback inhibitor. The negative relationship between Ghrelin and leptin implies a dual peripheral regulatory system controlling food intake. These preliminary observations need further examination in order to define the role of Ghrelin as a potential hormone regulating growth and nutrition.
08 - 11 Apr 2002
British Endocrine Societies