Physiological approaches to determining gut endogenous amino acid flows in the mammal

Abstract

Endogenous nitrogen and amino acid losses are associated with the digestion process. Different methods can be used to distinguish between gut endogenous and exogenous amino acid flows. These methods include feeding N-free diets, the regression approach, the use of enzyme hydrolysed proteins coupled with ultrafiltration and the use of markers (e.g., homoarginine, enzyme hydrolysed casein, 15N-labelled protein, 15N-leucine). All of the methods described have their limitations, but they have allowed major advances to be made in the measurement and understanding of endogenous amino acid secretion, reabsorption, flow and excretion.

Studies on N-metabolism in different gastrointestinal sections of sheep using the digesta exchange technique. 2. Passage of endogenous nitrogen

“…The most used and best suited precursor for endogenous N is the TCA soluble fraction of blood plasma (Souffrant et al, 1993;Krawielitzki et al, 1990;Van Leeuwen et al, 1994;Voigt et al, 1996;LammersWienhoven et al, 1998), which was chosen also in the present experiments. This, however, is a simplification, which can lead to endogenous N values being either overestimated (Souffrant et al, 1993;Lien et al, 1997;Leterme et al, 1998) or underestimated (Souffrant et al, 1986;Moughan et al, 1998). Despite these reservations, the 15 N dilution method is potentially useful for studying the factors that influence the secretion of endogenous N (Souffrant et al, 1986;Moughan et al, 1998).…”

Amino acid availability: aspects of chemical analysis and bioassay methodology

“…Over the last decade a considerable amount of research has been undertaken to develop alternative approaches to the protein-free dietary stratagem and to elucidate the effect of protein nutrition on endogenous ileal amino acid losses. The various methods and experimental approaches that have been developed to allow determination of endogenous amino acid losses at the terminal ileum are listed in Table 6 and have been discussed in detail (Lien et al 1997;Nyachoti et al 1997;Fuller & Reeds, 1998;Moughan et al 1998;Hess et al 1998Hess et al , 2000.…”

“…For the amino acid lysine, structurally unaltered molecules can be accurately determined using chemical methods (for example, FDNB-lysine assay; see earlier, p. 130), but there is evidence (Hurrell & Carpenter, 1981) that the unaltered or chemically available molecules may not be fully Table 6. Alternative approaches to the protein-free method, for the determination of endogenous ileal amino acid flows in mammals (from Nyachoti et al 1997;Fuller & Reeds, 1998;Moughan et al 1998; Method Linear regression Synthetic amino acid based diets Protein-free diets with intravenous amino acid infusion Natural proteins devoid of specific amino acids Guanidination of proteins Enzymically hydrolysed protein and ultrafiltration Isotopes (labelling of diet or body) Mathematical estimation based on endogenous or exogenous amino acid patterns Table 7. Amounts of acid-hydrolysed lysine, 1-fluoro-2, 4-dinitrobenzene (FDNB)-lysine, reactive lysine and absorbed reactive lysine in a heated casein-glucose mixture (from AcidAbsorbed hydrolysed* FDNB Reactive † reactive ‡ Lysine (g/100 g) 2·60 1·91 1·98 1·40…”

Modelagem da ingestão, retenção e excreção de nitrogênio e fósforo pela suinocultura gaúcha

“…Os resultados simulados dos fluxos de N e P em condições de média-alta tecnologia são coerentes com aqueles apresentados em situações experimentais (LENIS et al, 1999, NYACHOTI et al, 2000, em modelos de digestão (RIVEST et al, 2000) ou de metabolismo (MOUGHAN et al, 1998). Os ajustes teóricos de ingestão e utilização metabólica do N e P utilizados no MSUINP/RS respondem razoavelmente bem, mas necessitam de uma parametrização mais mecanicista.…”