Non-protein energy source in parenterally fed weanling rats influences growth, body composition and skeletal muscle protein turnover

Abstract Comparison was made between three total parenteral nutrition (TPN) regimens given to young, weanling rats for 5 days. The three isoenergetic and isonitrogenous regimens contained different ratios of glucose to lipid as non-protein energy sources, being composed of 100% glucose; 67% glucose/33% fat; and 50% glucose/50% fat respectively. Amino acid content was identical for each regimen. Body weight gain, carcass water and energy content, and in vitro skeletal muscle protein synthesis and degradation rates, were measured. All rats gained weight, but those receiving TPN with 100% of non-protein energy as glucose gained the most wet (live) and dry weight. Energetic efficiency was also significantly higher in this group. However, carcass analysis showed that much of the weight gain in this group was probably due to fat deposition. Although the two TPN groups receiving fat emulsion in addition to glucose gained less weight and had lower energetic efficiencies, weight gain was achieved with a comparatively smaller increase in fat deposition compared to the glucose-only group. In vitro rates of protein synthesis in skeletal muscle were significantly higher in the group receiving 100% glucose, but protein degradation rates in this group were grossly elevated. Protein synthesis rates in the groups receiving lipid were less, but degradation rates were also lower. The results suggest that optimal net protein balance in skeletal muscle was achieved in the group receiving 67% glucose: 33% lipid as the non-protein energy source.