Zinc Deficiency Increases Hypothalamic Neuropeptide Y and Neuropeptide Y mRNA Levels and Does Not Block Neuropeptide Y–Induced Feeding in Rats

Abstract

Zinc deficiency reduces intake and produces an unusual ∼3.5-d cycle of intake in rats. The mechanism underlying the anorexia and cycling has not yet been defined; current hypotheses suggest that alterations in amino acid metabolism and neurotransmitter concentrations may be a part of this anorexia. Recent reports indicate that appetite-stimulating neuropeptide Y (NPY) may be elevated during zinc deficiency. This suggests that a resistance to NPY may exist during zinc deficiency because NPY levels are high, yet appetite is low. The purpose of this study was to measure NPY peptide and mRNA concentrations during zinc deficiency in specific nuclei of the hypothalamus in which peptide and mRNA for NPY are known to be associated with appetite, and also to determine whether zinc-deficient rats are responsive to central infusions of NPY. Both NPY peptide levels in the paraventricular nucleus and NPY mRNA levels in the arcuate nucleus were higher (P < 0.05) in zinc-deficient rats than in zinc-adequate rats. When rats were administered exogenous NPY to the paraventricular nucleus, both zinc-deficient and zinc-adequate rats responded similarly by increasing food intake. These results suggest that NPY is elevated during zinc deficiency in an attempt to restore normal food intake levels, rather than being reduced and thereby contributing to the anorexia associated with zinc deficiency. During zinc deficiency, NPY receptors are able to bind NPY and initiate an orexigenic response.