NEUROPEPTIDE-Y IN RELATION TO CARBOHYDRATE INTAKE, CORTICOSTERONE ANDDIETARY OBESITY

Neuropeptide Y (NPY) is known to stimulate eating behavior and to be r elated to behavioral patterns of carbohydrate ingestion. The present r eport investigates this relationship further to: (1) characterize the specific NPY projection activated in different dietary paradigms; (2) understand associated changes in circulating hormones that may mediate dietary effects on NPY neurons; and (3) determine whether endogenous NPY in conditions with macronutrient diets can be linked to body fat. Male albino Sprague-Dawley rats were tested in two feeding paradigms, one in which the rats were given a choice of the macronutrients, carbo hydrate, fat or protein, or the other involving a single diet varying in carbohydrate or fat content. These studies consistently demonstrate a close association between the ingestion of carbohydrate and NPY lev els, specifically in the arcuate nucleus (ARC) and medial portion of t he paraventricular nucleus (PVN) of the hypothalamus. In addition to r evealing increased NPY activity in animals that naturally select high carbohydrate when given a choice of macronutrients, a single diet with 65% carbohydrate (10% fat), compared to a control diet with 45% carbo hydrate (30% fat), significantly potentiates NPY gene expression and N PY-immunoreactivity, as determined by in situ hybridization and immuno histochemistry. A further lowering of carbohydrate to 15% has little e ffect on NPY. Studies of medial hypothalamic fragments in vitro also r eveal enhanced NPY release from hypothalamic tissue taken from rats ma intained on a high-carbohydrate diet. Together with NPY, circulating c orticosterone (CORT) levels are also highest in a high-carbohydrate co ndition and positively correlated with NPY in the ARC. An association between NPY and adiposity in these dietary conditions is indicated by significantly higher levels of NPY in the medial PVN in rats with high body fat, whether consuming a high-carbohydrate or high-fat diet. Thi s evidence, linking NPY to carbohydrate intake and circulating CORT, s uggests a role for this peptide in glucose homeostasis that is normall y exhibited under conditions when carbohydrate stores are low. Disturb ances in this homeostatic process, associated with hyperinsulinemia an d higher levels of NPY, become evident with only a moderate rise in bo dy fat on a high-carbohydrate as well as high-fat diet. (C) 1998 Elsev ier Science B.V. All rights reserved.