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This Article Full Text (PDF) All Versions of this Article: jas.2008-1495v1 87/5/1747    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kraft, G. Articles by Savary-Auzeloux, I. Search for Related Content PubMed PubMed Citation Articles by Kraft, G. Articles by Savary-Auzeloux, I.

Nitrogen- and energy-imbalanced diets affect hepatic protein synthesis and gluconeogenesis differently in growing lambs

G. Kraft^*, D. Gruffat^*, D. Dardevet, D. Rémond, I. Ortigues-Marty^* and I. Savary-Auzeloux^*

^* INRA Theix, Herbivores Research Unit, UR 1213 F63122 Saint-Genès-Champanelle INRA Theix, Human Nutrition Unit UMR 1019 F63122 Saint-Genès-Champanelle

Savary{at}clermont.inra.fr

Abstract

The aim of this study was to assess the metabolic fate of AA (endogenous or export protein synthesis, gluconeogenesis, or oxidation) after an imbalanced supply of energy and N in the diet of growing lambs. Eighteen INRA 401 lambs (3 mo old, 29.7 ± 0.45 kg BW) were fed 3 experimental diets, one providing a N and energy supply according to recommended allowances (CON), one with 23% lower N supply relative to energy (LN) , and one with 19% lower ME supply relative to N (LE). Animals were assigned to 6 blocks of 3, each animal receiving 1 of the 3 diets, and the animals from each block were slaughtered on the same day. Liver slices from these lambs were incubated in a minimum salt medium (Krebs-Henseleit) containing physiological concentrations of propionate and AA as energy and N sources, similar across all 3 treatments. Protein synthesis (endogenous and export) using [U-¹⁴C]valine and [³⁵S]methionine, gluconeogenesis from [1-¹⁴C]propionate and [U-¹⁴C]alanine, and oxidation were measured. A relative sparing of AA at the liver level was observed with the LN diet due to reduced urinary N (-42%, LN vs. CON, P < 0.001). The AA were also directed towards anabolic purposes in the LN diet via an increased endogenous and total export protein synthesis (+51%, LN vs. CON, P = 0.01) (also observed for fibrinogen synthesis but not for albumin or transferrin) associated with a tendency for increased gluconeogenesis from alanine (+58%, LN vs. LE, P = 0.08). On the other hand, the LE diet resulted in a marked loss of N in urine (+24%, LE vs. CON, P < 0.05), but no notable effect of the LE diet was demonstrated for protein synthesis or gluconeogenesis ex vivo. These data demonstrate a more efficient utilization of AA for anabolic purposes in the lambs fed LN, probably via an activation of some AA-transport systems, to address the shortage of nitrogenous nutrients in the LN diet. By contrast, no such adaptation occurs in the LE lambs, probably because the regulatory mechanisms that prevail in this case are the nutrient supply or hormones that are not altered in our ex vivo experimental model.

Key Words: amino acid • ex vivo • gluconeogenesis • lamb • liver • protein synthesis