Endocrine Abstracts

Introduction: Ghrelin - a growth hormone (GH) secretagogue - presents a circadian rhythm with higher nocturnal concentration (similar to GH). As daily ghrelin production depended on food intake and nutritional state, we decided to assess ghrelin concentration at 60th at 90th minute after falling asleep and at 6:00 am (after 12 hours of fasting), and compare the results to determine the differences between nocturnal and morning ghrelin release in short children, both with idiopathic short stature (ISS) and with growth hormone deficiency (GHD). We also decided to correlate nocturnal and morning ghrelin concentration with the nocturnal GH concentration, measured at the same time points, as well as with the insulin-like growth factor I (IGF-I) and the maximal GH concentration during stimulating tests.

Methods: In 19 short children (aged: 10.36 ± 3.06 years), ghrelin and GH concentration at 60’ and 90’ after falling asleep, as well as fasting ghrelin and IGF-I concentrations were measured. Moreover, two GH-stimulating tests were performed to establish the diagnosis: ISS or GHD.

Results: A significant correlation was observed: a) positive-between nocturnal ghrelin (both at 60’ and at 90’) and fasting ghrelin concentrations; b) positive - between ghrelin at 60’ and nocturnal GH concentrations (both at 60’and at 90’) ; c) negative - between ghrelin at 60’ and IGF-I concentrations; d) negative - between ghrelin concentrations at 60’ and body mass index of children.

Conclusions: 1. In short children, fasting ghrelin indirectly reflects its nocturnal concentration, however it is significantly higher than the nocturnal one.

2. Despite the fact that ghrelin appears to stimulate GH secretion at night, and IGF-I is the main peripheral mediator of GH activity, it appears that in short children the lower levels of IGF-I the higher nocturnal secretion of ghrelin. This indicates inadequate GH synthesis or effects on peripheral IGF-I production in these cases.

3. Additionally, a higher nutritional state is an independent factor which influences lower nocturnal ghrelin secretion.