l-Arginine supplementation in pigs decreases liver protein turnover and increases hindquarter protein turnover both during and after endotoxemia

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Abstract
Background: Accumulating evidence suggests that l-arginine, under conditions of septicemia, not only enhances immune function but also improves protein metabolism. Objective: Because the effect of l-arginine administration on the protein metabolism of different organs is unknown, the aim of the study was to elucidate the effects of exogenous supplementation of l-arginine during endotoxemia on the in vivo protein metabolism of individual organs and at the whole-body level. Design: Female pigs were cannulated with catheters in the aorta and the splenic, caval, portal, hepatic, and renal veins, enabling measurements across the hindquarter, portal-drained viscera, liver, and kidneys. Endotoxemia was induced by a 24-h continuous intravenous infusion of endotoxin (3 μg·kg body wt−1·h−1). At 8 h, an intravenous infusion of l-arginine was started (n = 8). Control pigs (n = 6) received l-alanine. At 24 h, blood was sampled. After cessation of the endotoxin infusion, l-arginine and l-alanine infusions were continued as a supplement in the enterally infused diet. At 48 h, blood samples were obtained during the postendotoxemic and nutritionally supported conditions. Stable isotopes were used to assess protein metabolism and phenylalanine hydroxylation. Results: Both during and after the endotoxin challenge, l-arginine administration enhanced protein synthesis and degradation across the hindquarter and simultaneously reduced protein synthesis and degradation in the liver at equal rates. Protein turnover across the kidneys and portal-drained viscera remained unaffected. After endotoxemia, l-arginine infusion decreased whole-body protein turnover without affecting the net protein balance. Conclusion:l-Arginine administration affects protein turnover of the muscle area and the liver oppositely.