Clarification of the mechanism involved in orexigenic action by oral zinc ingestion

We investigated the role of zinc in regulation of food intake using male SD rats during early-stage of zinc deficiency (the 3rd day of the feeding) without decreased zinc concentrations in tissues (hypothalamus and liver). As a result, we found that orally but not intraperitoneal administered zinc stimulates food intake in the short-term zinc-deficient rats. The mRNA expressions of hypothalamic peptides, such as orexin (OX) and neuropeptide Y (NPY), were increased after oral administration of zinc to increase food intake. Pretreatment with an antagonist for the NPY Y ₁ receptor or the orexin OX ₁ receptor blocked orexigenic activity by zinc administration. The stimulation of food intake by oral administration of zinc was also abolished by vagotomy. Taken together, our results indicate that zinc stimulates food intake in short-term zinc-deficient rats through the afferent vagus nerve followed by activating the hypothalamic peptide associated with food intake regulation. This study showed the first evidence that gastrointestinal zinc signal is indispensable for the food appetite induction in the experimentally anorexigenic rat. However, since it has not yet been clarified the mechanism involved in zinc sensing by the epithelial membrane of the gastrointestinal tract, further detailed investigations are necessary.