La ghréline : seule hormone orexigène connue

Ghrelin is a 28-amino acid acylated peptide predominantly produced by the stomach peripherally as well as the pituitary and the hypothalamus in the brain. Originally discovered as the endogenous ligand of the orphan growth hormone secretagogue receptor, it is also involved in the regulation of food intake and body weight. Ghrelin is the first known orexigenic hormone. Human plasma ghrelin levels sharply increase before and decrease after every meal. Plasma ghrelin levels correlate negatively with the magnitude of energy stores. Obesity is characterized by low ghrelin plasma concentration, conversely patients suffering anorexia or cachexia display high levels. Weight loss triggers an increase in ghrelin levels while the opposite is observed during weight gain. The role for ghrelin in the regulation of appetite and body weight is mediated, at least in part, via the activation of neurons in the hypothalamus that coexpress neuropeptide Y (NPY) and agouti-related protein (AgRP), two anabolic neuropeptides. Ghrelin appears as the hormone that coordinates GH secretion and food intake to assure an optimal growth and a steady energy balance. Due to its role in the regulation of body weight, ghrelin holds promise as a target for both medical and surgical approaches to obesity treatment.