Immune response and leucine oxidation in oral and intravenous fed rats.

A comparison was made between oral and intravenous nutrition with respect to the route of nutrient administration on leucine oxidation and the immune response. Rats were either fed an oral liquid diet or a comparable amount of energy and amino acids by vein. Groups of rats were used daily for 7 days to determine the percentage of L-[1-14C]-leucine oxidized and the ability of the lymphocytes to respond to stimulation. The intravenous fed rats continually lost 60 to 80 mg more of nitrogen per day in the urine than oral fed rats. The percentage of C-14 from leucine found in breath in 4 h was 13 to 15% of the dose for the oral rats and 25 to 27% for the parenteral fed rats. Lymphocytes reactivity remained unchanged over 7 days for the oral fed rats while the intravenous fed rats were depressed by day 2 to 3 and remained depressed through day 7. These data indicate that nitrogen provided by vein is not handled efficiently as that taken per os, and the requirements for intravenous nutrition are different than those needed for oral food intake.