Effect of intravenous or intragastric nutrients on food intake in rats

A series of experiments were performed to determine which components of total parenteral nutrition (TPN) reduce spontaneous food intake (SFI) and to what degree. In Experiment 1, rats were infused with TPN (15% dextrose + 5% fat + 4.3% amino acid) or with one of its three components given independently at the final concentration of TPN for 3 days via an intravenous (iv) catheter. Each solution, at 3 ml/hr, provided a different amount of calories (TPN = 85, dextrose = 37, fat = 36, and amino acid = 12 kcal/day), representing about 120, 50, 50, and 20% of the rat's spontaneous caloric intake, respectively. TPN, dextrose, and fat significantly reduced SFI compared to the infusion of normal saline; however, amino acid failed to reduce SFI. Experiment 2 was carried out to investigate the relative contributions that pre- and postabsorptive mechanisms make in the regulation of SFI. Each rat in four different groups was infused with one of four isocaloric nutrient solutions through an iv catheter and a gastrostomy (ig) for separated periods of time. Nutrient solutions at 3 ml/hr provided each 32 kcal/day (50% of requirements): 13% dextrose, 4.5% fat, 11.4% amino acid, and a mixture (6.4% dextrose + 1.6% fat + 1.7% amino acid). Each solution, either iv or ig, reduced SFI compared to normal saline infused via the same route. However, neither the route of administration nor the nature of different nutrients caused significant differences in SFI reduction.