Effects of dietary macronutrient composition on exogenous neuropeptide Y’s stimulation of food intake in chicks

Abstract

In mammalian models it is well documented that the potent orexigenic factor, neuropeptide Y (NPY) causes preferential intake of high carbohydrate and fat diets; however, information on this is limited in non-mammalian species. The purpose of this study was to determine the influence of dietary macronutrient composition on NPY’s orexigenic effect in chicks. Three isocaloric diets were formulated: high carbohydrate, fat and protein. In Experiment 1, chicks were fed the three diets and received intracerebroventricular injections of 0.2 or 2.0nmol NPY. Chicks that consumed the high carbohydrate and protein diets had a non-dose dependent similar magnitude of increased food intake after NPY injection, but those on the high fat diet had a dose dependent food intake increase. In Experiment 2, when chicks were given free access to all three diets, injection of 0.2nmol NPY caused preferential increase in intake of only the high protein diet whereas 2.0nmol NPY caused preferential increases in of both high carbohydrate and protein diets. Neither dose affected high fat diet intake. In Experiment 3, chicks were raised on one of the three diets and then switched to the others. When chicks were raised on the high fat and protein diets and then switched to the other diets, stimulation of food intake occurred for the same duration, 180min. However, when chicks were raised on the high carbohydrate and then switched to high fat, NPY injection caused a sustaining increase in cumulative food intake that lasted the entire observation period. These results suggest that NPY has selective effects on consumption of carbohydrate, fat and protein in chicks, and that diet in turn affects the NPY-mediated response in food intake, with a high fat diet enhancing NPY sensitivity that is associated with a greater magnitude and duration of feeding response. In turn, NPY caused preferential protein and carbohydrate intake instead of fat intake (in this order of preference), when chicks had the opportunity to select their diet. Finally, these results reinforce that NPY increases food intake independent of diet.