Protein restriction and dexamethasone as a model of protein hypercatabolism in dogs: Effect of glutamine on leucine turnover

To determine (1) whether protein restriction, combined with glucocorticoste roid treatment, can be used as a hypercatabolic model and (2) if so, whethe r glutamine attenuates protein wasting in this model, the effects of protei n restriction, dexamethasone, and glutamine on leucine metabolism were asse ssed in dogs. A control group (n = 8) received a maintenance diet; another group (n = 8) received a protein-restricted diet either (1) alone; (2) alon g with a jr-day corticoid treatment; or (3) along with a 7-day corticoid tr eatment and a ir-hour intravenous (IV) glutamine infusion. The last day of each regimen, dogs underwent an IV isotope infusion in the fasting state, w ith a B-hour (NaHCO3)-C-13 infusion to assess CO2 production, and immediate ly thereafter, a I-hour C-13-leucine infusion to assess leucine appearance rate (Ra), oxidation (Ox), and nonoxidative leucine disposal (NOLD), expres sed as mu mol.kg(-1).h(-1). Protein restriction was associated with a 24% d ecline in leucine Ra (223 +/- 16 v 298 +/- 17; P < .01), an index of whole body proteolysis, and a 29% decline in NOLD (180 +/- 15 v 223 +/- 13; P < . 01), an index of whole body protein synthesis. In the protein-restricted gr oup, dexamethasone treatment was associated with a 32% increase in Ra, (295 +/- 28 v 223 +/- 16; P < .05), a 186% increase in Ox (120 +/- 14 v 43 +/- 4; P < .001), with no change in NOLD, when compared with the protein-restri cted alone. After protein restriction + dexamethasone, glutamine infusion i nduced a 40% increase in plasma glutamine (1,090 +/- 70 v 780 +/- 29 mu mol .L-1; P < .01), but failed to after Ra, Ox, or NOLD. These results suggest that (1) in dogs, protein restriction combined with a 7-day course of dexam ethasone results in alterations in leucine kinetics similar to those observ ed in stress-induced protein wasting in humans, and (2) in that model, a ir -hour IV glutamine infusion in the fasting state does not significantly att enuate protein wasting. Copyright (C) 2001 by W.B. Saunders Company.