Interorgan amino acid exchange in humans: consequences for arginine and citrulline metabolism

M.C. van de Poll, M.P. Siroen, P.A. van Leeuwen, P.B. Soeters, G.C. Melis, P.G. Boelens, N.E. Deutz, C.H. Dejong

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

BACKGROUND: The liver plays a central role in amino acid metabolism. However, because of limited accessibility of the portal vein, human data on this subject are scarce. OBJECTIVE: We studied hepatic amino acid metabolism in noncirrhotic fasting patients undergoing liver surgery. DESIGN: Twenty patients undergoing hepatectomy for colorectal metastases in a normal liver were studied. Before resection, blood was sampled from a radial artery, portal vein, hepatic vein, and renal vein. Organ blood flow was measured by duplex ultrasound scan. RESULTS: The intestine consumed glutamine and released citrulline. Citrulline was taken up by the kidney. This was accompanied by renal arginine release, which supports the view that glutamine is a precursor for arginine synthesis through an intestinal-renal pathway. The liver was found to extract citrulline from this pathway at a rate that was dependent on intestinal citrulline release (P < 0.0001) and hepatic citrulline influx (P = 0.03). Fractional hepatic extractions of citrulline (8.4%) and arginine (11.5%) were not significantly different. Eighty-eight percent of arginine reaching the liver passed it unchanged. Splanchnic citrulline release could account for one-third of renal citrulline uptake. CONCLUSIONS: This is the first study of hepatic and interorgan amino acid metabolism in humans with a normal liver. The data indicate that glutamine is a precursor of ornithine, which can be converted to citrulline by the intestine; citrulline is transformed in the kidneys to arginine. Hepatic citrulline uptake limits the amount of gut-derived citrulline reaching the kidney. These findings may have implications for interventions aimed at increasing systemic arginine concentrations.
Original languageEnglish
Pages (from-to)167-172
JournalAmerican Journal of Clinical Nutrition
Volume85
Issue number1
DOIs
Publication statusPublished - 1 Jan 2007

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