Quantitative role of splanchnic region in leucine metabolism: L-[1-13C,15N]leucine and substrate balance studies

Abstract

The role of the splanchnic region (Sp) in whole body leucine metabolism was assessed in six chronically catheterized fasting mongrel dogs and in eight dogs during constant enteral feeding of a complete amino acid solution (0.24 g.kg-1.h-1). We used primed continuous intravenous infusions of L-[1-13C,15N]leucine and L-[1-14C]leucine and measurements of arteriovenous isotope and leucine balance across the gut, liver, and Sp. In the fasted condition, 3.5% of arterial leucine supply was oxidized in the Sp, accounting for 13% of total body leucine oxidation, with 10% by liver. With amino acid feeding 1) leucine carbon and nitrogen fluxes and oxidation were increased (P less than 0.01) at the whole body level; 2) the percent of whole body leucine oxidation occurring in the Sp and liver increased (P less than 0.01) to 41 and 27%, respectively; 3) fractional metabolic utilization of leucine delivered to the Sp was reduced (P less than 0.01) from 47 to 35%; 4) the deamination rate of leucine in the gut was increased (P less than 0.05), along with an increased reamination rate of alpha-ketoisocaproic acid in the Sp (P less than 0.05). These findings reveal that the Sp accounts for a small fraction of whole body leucine oxidation during the fasting condition, but it plays a quantitatively important role in total body leucine oxidation during amino acid feeding; the gut and liver play cooperative roles in controlling leucine supply to peripheral tissues.

Adult Trichostrongylus colubriformis infection did not affect protein synthesis rate in whole-body, intestinal, hepatic and skeletal muscle tissues of lambs fed fresh Lucerne (Medicago sativa)

“…This was also observed in a previous study (Bermingham et al 2006). Additionally, differences in whole-body estimates of AA ILR due to differences in the metabolism of the labeled isotope have been observed previously (Krempf et al 1990;Yu et al 1990). …”

Tracking the oxidative kinetics of carbohydrates, amino acids and fatty acids in the house sparrow using exhaled 13CO2

“…Several studies of mammals have compared the fates of intravenous and oral doses of leucine, permitting researchers to estimate that between 17-41% of exogenous leucine is oxidized immediately (i.e. first-pass oxidation) upon absorption by splanchnic tissues (Cortiella et al, 1988;Crenn et al, 2000;Hoerr et al, 1991;Istfan et al, 1988;Luiking et al, 2005;Metges et al, 2000;Stoll et al, 1998;Yu et al, 1990). Although less is known about rates of first-pass glycine oxidation by splanchnic tissues, Daenzer et al (Daenzer et al, 2001) suggested that in humans, as much as half the exogenous glycine may be lost to first-pass oxidation.…”

Enteral Tryptophan Requirement Determined by Oxidation of Gastrically or Intravenously Infused Phenylalanine Is Not Different from the Parenteral Requirement in Neonatal Piglets

“…Therefore, because amino acid kinetic measurements are affected by route of isotope infusion, requirement estimates determined using oral versus IV infusion may be different. Although several investigators have studied the effect of the route of tracer administration on amino acid kinetics (11)(12)(13)(14)(15)(16)(17), only our group (10) has examined the effect of the route of isotope administration on amino acid requirement estimates. In that study, we determined that route of isotope infusion had no effect on oral lysine requirements in healthy human adults.…”