Splanchnic and whole body L-[1-13C,15N]leucine kinetics in relation to enteral and parenteral amino acid supply.

Abstract

The effect of the route of administration of a complete amino acid solution (0.24 g.kg-1.h-1) on leucine (Leu) and alpha-ketoisocaproate (KIC) metabolism in the splanchnic region (Sp) was assessed in nine chronically catherized mongrel dogs receiving, for 6 h, amino acids by jugular vein (PN feeding). Results were compared with those obtained previously [Y. M. Yu, D. A. Wagner, E. E. Tredget, J.A. Waleszewski, J. F. Burke, and V. R. Young. Am. J. Physiol. 259 (Endocrinol. Metab. 22): E36-E51, 1990] in eight dogs similarly studied but given amino acids by constant enteral feeding (EN). We used primed continuous intravenous infusions of L-[1-13C,15N]Leu and measurements of arteriovenous isotope and Leu balance across the gut, liver, and Sp to estimate parameters of whole body and organ Leu metabolism [Leu-N and Leu-C flux, Leu----KIC; KIC----Leu, Leu oxidation and rates of Leu appearance (B) from and disappearance (S) into proteins]. Whole body Leu kinetics were the same for both routes of amino acid administration. With PN, KIC----Leu, Leu----KIC, and total metabolic processing were lower than for EN in Sp, and overall Leu balance (S - B) was higher in Sp for EN. Leu appearance from protein breakdown in gut was higher with PN. The rate of KIC----Leu was higher in liver for EN. These findings reveal that route of amino acid (Leu) administration, under these acute feeding conditions, alters the processing and metabolic fate of Leu in Sp but that whole body parameters of Leu metabolism are stable. The implications of these metabolic findings in relation to the maintenance of intestinal function and integrity are discussed.