MACRONUTRIENT TYPE INDEPENDENTLY OF ENERGY-INTAKE MODULATES HYPOTHALAMIC NEUROPEPTIDE-Y IN LONG-EVANS RATS

Neuropeptide Y (NPY) induces a robust feeding response when it is inje cted in the hypothalamus. It stimulates both carbohydrate and fat inta kes. Diets rich in either macronutrient are known to induce obesity an d to modify feeding behavior. The aim of the present study was to dete rmine the effects of long-term ingestion of these diets on hypothalami c NPY in relation with food intake and body weight gain and compositio n. For this purpose, three groups of weanling Long-Evans rats were fed either a well-balanced diet, a high-carbohydrate (HC) diet (high star ch plus 25% sucrose solution), or a high-fat (HF) diet during 14 weeks . Body weight and food intake were recorded during this period. At the end of the experiment, NPY was measured in several microdissected bra in areas, and some adipose tissues (AT) depots were sampled. HF rats w eighed significantly more than the two other groups (p < 0.02). They w ere also fattier (+30-50% in AT weights; p < 0.01). Energy intake (EI) of the HC rats was significantly greater than that of the control (+1 5%; p < 0.02) and HF rats (+34%; p < 0.01) during the week preceding k illing. EI of HF rats over the whole experiment was lower than that of the two other groups (p < 0.01). NPY concentrations were lower in the HF and HC rats than in the control rats in two hypothalamic areas onl y: in the arcuate nucleus (ARC) (-28% (HC vs. control); p < 0.02 and - 54% (HF vs. control); p < 0.001) and in the parvocellular part of the paraventricular nucleus (PVN) (-48% (HF vs. control); p < 0.001). Thes e results indicate that the long-term ingestion of HC and HF diets inf luences NPY in areas where it is synthesized (ARC) and released (PVN), whereas at short term, the PVN was uniquely concerned as shown by a p revious study. These variations in the ARC-PVN axis might be considere d to be counterregulatory mechanisms necessary for limiting overconsum ption of food as well as fat deposition.