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 injected in the hypothalamus. It stimulates both carbohydrate and fat intakes. Diets rich in either macronutrient are known to induce obesity and to modify feeding behavior. The aim of the present study was to determine the effects of long-term ingestion of these diets on hypothalamic NPY in relation with food intake and body weight gain and composition. For this purpose, three groups of weanling Long-Evans rats were fed either a well-balanced diet, a high-carbohydrate (HC) diet (high starch 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 brain areas, and some adipose tissues (AT) depots were sampled. HF rats weighed significantly more than the two other groups (p < 0.02). They were 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 (+15%; p < 0.02) and HF rats (+34%; p < 0.01) during the week preceding killing. 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 only: 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). These results indicate that the long-term ingestion of HC and HF diets influences NPY in areas where it is synthesized (ARC) and released (PVN), whereas at short term, the PVN was uniquely concerned as shown by a previous study. These variations in the ARC-PVN axis might be considered to be counterregulatory mechanisms necessary for limiting overconsumption of food as well as fat deposition.