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Glutamine degradation in the gut of conventional and germ-free rats
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PROTEIN SYNTHESIS IN RAT JEJUNUM:- PRECURSOR POOLS AND ADAPTATION TO PROTEIN/ENERGY RESTRICTION. C J Egan, M J Rennie. Dept of Physiology, University of Dundee, Scotland. We have investigated i) the relative importance of luminal and vascular amino acids as protein synthetic precursors and ii) alterations of dietary protein/energy on protein turnover of jejunal mucosa. In Wistar rats (230 ?1 log) studied postabsorptively and after 72 h fasting, protein synthesis (ks) was measured in jejunal mucosa 10 mins after flooding injection of 150 mM L-3H-Phenylalanine (PHE) into the bloodstream and 150 mM L-14C-PHE into the lumen. In fed and fasted rats, incorporation of 3H:14C was 15:l suggesting that the blood is the major precursor pool for mucosal kS. In isolated vascularly and luminally perfused jejunum the maximum first pass incorporation of luminal amino acids into mucosa was 15% of total synthesis. A 50% fall in mucosal protein mass occurred after 72 h fasting but ks was normal at 132 + 8%/day indicating an increase in protein breakdown (kb) or cell loss. k, was also measured using vascular 3H-PHE after 12 d of diets containing 0, 8, 27(control) and 64% protein. Mucosal protein was lost on the 0% diet; since ks was unchanged, kb or cell loss must have increased. On tlhe8% protein diet villus height increased from 406 + 37 urn to 657 + 70 urn after 2d and continued to increase to a plateau of 825 ? 56 vrnafter 8d, when body growth resumed; there was also a 50% rise in mucosal protein mass by 12d and, although ks rose by 24% (to 165 Z! 20%/d), kb must also have increased. Uniquely, in rats on the 8% diet, the gut extracted more amino acids from arterial blood, presumably allowing mucosal growth, than it lost to the portal vein. There were no effects on protein mass or ks of the 64% diet. The results indicate the capacity of the mucosa to maintain (during fasting and zero protein intake) or adaptively increase (during low protein intake) protein synthesis, presumably with the result of preserving/enhancing absorptive function. Furthermore, the mucosal atrophy observed during TPN is unlikely to be due to lack of precursor luminal amino acids. Supported by the Joint Consultative Committee of the Milk Marketing Board, Dundee University, MRC and the Wellcome Trust.
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GLUTAMINE DEGRADATION IN THE GUT OF CONVENTIONAL AND tiERM-FREE RATS. P.A.M. van LeeuwH. de Jonge*, P.B. Soeters (Dept. of Surgery, University Hospital M aastricht, $pt. of Biochemistry, Erasmus University, Rotterdam, The Netherlands). Introduction. There is an increasing interest in glutamine metabolism since sepsis and catabolism are associated with intra- and extracellular glutamine depletion. Ninety percent of all nitrogen resulting from muscle proteolysis is released into the systemic circulation, not as the constituting amino acids, but as glutamine and alanine. Glutamine, acting as a non-toxic nitrogen carrier is therefore mostly degraded in the gut, although the exact site and pathways of this process have not been subject of study. Methods. We therefore harvested enterocytes (villous and crypt cells) from conventional and germ-free rats and incubated them in a Krebs-Ringer buffer solution, with and without addition of glutamine (1OmM) for 30 min. Ammonia, glutamine, alanine, ornithine and citrulline were determined. Results of incubation without (-) and with (+) glutamine are expressed as umol/mg DNA/30min (*=p
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PROTEIN SYNTHESIS IN RAT JEJUNUM:- PRECURSOR POOLS AND ADAPTATION TO PROTEIN/ENERGY RESTRICTION. C J Egan, M J Rennie. Dept of Physiology, University of Dundee, Scotland. We have investigated i) the relative importance of luminal and vascular amino acids as protein synthetic precursors and ii) alterations of dietary protein/energy on protein turnover of jejunal mucosa. In Wistar rats (230 ?1 log) studied postabsorptively and after 72 h fasting, protein synthesis (ks) was measured in jejunal mucosa 10 mins after flooding injection of 150 mM L-3H-Phenylalanine (PHE) into the bloodstream and 150 mM L-14C-PHE into the lumen. In fed and fasted rats, incorporation of 3H:14C was 15:l suggesting that the blood is the major precursor pool for mucosal kS. In isolated vascularly and luminally perfused jejunum the maximum first pass incorporation of luminal amino acids into mucosa was 15% of total synthesis. A 50% fall in mucosal protein mass occurred after 72 h fasting but ks was normal at 132 + 8%/day indicating an increase in protein breakdown (kb) or cell loss. k, was also measured using vascular 3H-PHE after 12 d of diets containing 0, 8, 27(control) and 64% protein. Mucosal protein was lost on the 0% diet; since ks was unchanged, kb or cell loss must have increased. On tlhe8% protein diet villus height increased from 406 + 37 urn to 657 + 70 urn after 2d and continued to increase to a plateau of 825 ? 56 vrnafter 8d, when body growth resumed; there was also a 50% rise in mucosal protein mass by 12d and, although ks rose by 24% (to 165 Z! 20%/d), kb must also have increased. Uniquely, in rats on the 8% diet, the gut extracted more amino acids from arterial blood, presumably allowing mucosal growth, than it lost to the portal vein. There were no effects on protein mass or ks of the 64% diet. The results indicate the capacity of the mucosa to maintain (during fasting and zero protein intake) or adaptively increase (during low protein intake) protein synthesis, presumably with the result of preserving/enhancing absorptive function. Furthermore, the mucosal atrophy observed during TPN is unlikely to be due to lack of precursor luminal amino acids. Supported by the Joint Consultative Committee of the Milk Marketing Board, Dundee University, MRC and the Wellcome Trust.
0.55
GLUTAMINE DEGRADATION IN THE GUT OF CONVENTIONAL AND tiERM-FREE RATS. P.A.M. van LeeuwH. de Jonge*, P.B. Soeters (Dept. of Surgery, University Hospital M aastricht, $pt. of Biochemistry, Erasmus University, Rotterdam, The Netherlands). Introduction. There is an increasing interest in glutamine metabolism since sepsis and catabolism are associated with intra- and extracellular glutamine depletion. Ninety percent of all nitrogen resulting from muscle proteolysis is released into the systemic circulation, not as the constituting amino acids, but as glutamine and alanine. Glutamine, acting as a non-toxic nitrogen carrier is therefore mostly degraded in the gut, although the exact site and pathways of this process have not been subject of study. Methods. We therefore harvested enterocytes (villous and crypt cells) from conventional and germ-free rats and incubated them in a Krebs-Ringer buffer solution, with and without addition of glutamine (1OmM) for 30 min. Ammonia, glutamine, alanine, ornithine and citrulline were determined. Results of incubation without (-) and with (+) glutamine are expressed as umol/mg DNA/30min (*=p
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