VAGOTOMY AND MERCAPTOACETATE INFLUENCE THE EFFECT OF DIETARY-FAT ON MACRONUTRIENT SELECTION BY RATS

We have previously shown that rats fed saturated fat prefer a high pro tein, low carbohydrate diet, whereas animals fed unsaturated fat prefe r a low protein, high carbohydrate diet. The purpose of the present st udy was to determine whether this ''saturated fat effect'' requires 1) the oxidation of the dietary fat and 2) an intact hepatic vagus nerve . Male Sprague-Dawley rats were vagotomized (hepatic branch) or sham-o perated and injected with either mercaptoacetate (fatty acid oxidation inhibitor) or saline. Next, half of each group was given saturated fa t (beef tallow) or unsaturated fat (corn oil) by gastric tube. All ani mals were given a choice between two mixed diets that differed in prot ein and carbohydrate. Sham-operated rats fed saturated fat ate more of the protein diet than did rats fed unsaturated fat. Vagotomy attenuat ed the intake of the protein diet in animals fed saturated fat. Mercap toacetate or vagotomy had no effect on diet selection in rats fed unsa turated fat. These data indicate that the effect of saturated fat on d iet selection requires an intact hepatic vagus and may be modulated by fatty acid oxidation. Furthermore, the mechanism for altering diet se lection can be induced after a single meal.