COMPARATIVE-EVALUATION OF THE QUANTITATIVE UTILIZATION OF PARENTERALLY AND ENTERALLY ADMINISTERED LEUCINE AND L-[1-13C,15N]LEUCINE WITHIN THE WHOLE-BODY AND THE SPLANCHNIC REGION

Background: The purpose of this study was to quantify the kinetic aspe cts of leucine metabolism in the whole body and within the splanchnic region when an amino acid mixture is administered by the enteral route as compared with administration by the parenteral route. Methods: Sev en chronically catheterized dogs were studied during an intragastric i nfusion of L-[1-C-13,-15-N]leucine with 0.24 g of complete amino acid mixture (kg-1.h-1) for 6 hours. The results are compared with those pr eviously reported for nine dogs studied under essentially identical ex perimental conditions except that the tracer and amino acid mixtures w ere given by vein. Results: At the whole body level, the various param eters of leucine metabolism (flux, oxidation, and disappearance into a nd release from proteins) were not significantly different among anima ls that were infused enterally and those that were infused parenterall y. Leucine metabolism within the splanchnic region and gut was more ex tensive for enteral administration than for parenteral administration. For the splanchnic region, 31.4%, 27.9%, and 6.0% of enterally admini stered leucine was used for protein synthesis, deamination, and oxidiz ation, respectively, compared with respective mean values of 19.5% (p < .001), 13.4% (p < .001), and 4.1% (p < .05) for parenterally adminis tered leucine. For liver, 4.8% of enterally administered leucine was o xidized compared with 2.3% (p < .001) of parenterally administered leu cine. These findings are qualitatively similar to those reported previ ously by us when comparing enteral and parenteral amino acid intakes b ut with an IV tracer infusion. Conclusion: Enteral administration seem s to be more effective than an acute parenteral feeding regimen, at le ast in maintaining leucine (protein) balance in gut tissues.