Preference and diet type affect macronutrient selection after morphine, NPY, norepinephrine, and deprivation

Abstract

The orexigenic agents morphine, neuropeptide Y (NPY), and norepinephrine (NE) and deprivation have been reported to induce selection of specific macronutrients: fat, carbohydrate (CHO), CHO, and fat, respectively. We utilized analysis of covariance to compensate for the influence of baseline preference on feeding induced by six experimental procedures: morphine, NPY, NE, 24 and 48 h food deprivation, and chronic dietary restriction. Rats received one of two dietary regimens: three macronutrient diets containing CHO, protein, or fat (regimen I) and two nutritionally complete diets that were high CHO or high fat (regimen II). Baseline preference significantly influenced dietary selection after all six experimental procedures studied in regimen I and after NPY, NE, 48 h food deprivation, and chronic dietary restriction in regimen II (covariate P < 0.05). In both dietary regimens, morphine (5 mg/kg) increased consumption of fat, NPY (5 micrograms icv) increased selection of CHO, and consumption of all diets was induced equally after NE injections (20 micrograms icv). After 24 or 48 h food deprivation, animals consumed more fat in regimen I and more CHO diet in regimen II. Restricting food intake by 20% increased fat and protein consumption in regimen I but had no effect in regimen II. Diet selection is affected by prior preference, feeding stimulus, and type of diet choice presented.