Effects of ghrelin on circulating neuropeptide Y levels in humans.

OBJECTIVE: Ghrelin is a 28 amino-acid peptide with a strong GH-releasing activity and a complex role in regulation of appetite, fuel utilization, body weight and composition. Neuropeptide Y (NPY) is a well-known stimulator of pathways favouring food intake and energy storage. Recently, studies in rodents suggested a possible mediation of ghrelin action by NPY. In contrast, until now no evidence of ghrelin-NPY interaction in humans has been provided. In the present study, we examined whether ghrelin influences NPY secretion in normal men.

SUBJECTS AND DESIGN: Twelve healthy normal men (aged 24-35 years; body mass index (BMI) 22.3+/-0.93 kg/m2) were tested twice at 08.00 AM on two different days, in random order at weekly intervals, after an overnight fast and rest in bed. An intravenous bolus of 1 microg/kg body weight ghrelin (esperimental test) or an equal amount of normal saline (control test) was injected at time 0. Blood was taken before and over 90 minutes after injections, and was used for the measurement of plasma NPY levels.

RESULTS: Plasma levels of NPY slightly, but significantly rose in response to ghrelin, with a mean peak level at 15 min after injection, whereas no significant change was observed after saline administration.

MAIN FINDING: Our results show a significant enhancement of plasma NPY levels under ghrelin stimulation.

CONCLUSIONS: To our knowledge, this is the first demonstration of a ghrelin-NPY interaction in humans, which may suggest a possible mediation of ghrelin action by NPY in humans.

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