Amino acid metabolism during platelet storage for transfusion

Previous studies indicated that the concentration of ammonia rises during storage of platelet concentrates (PC) at 22 degrees C for transfusion and that fuels other than glucose are important for metabolism. Therefore, in the current study, we measured the concentrations of 17 plasma amino acids during PC storage; 16 of these either rose or were unchanged while the concentration of glutamine fell to zero by day 4. As the concentration of glutamine fell, the concentration of glutamate rose with a relationship suggesting that 65-75% of the glutamine was metabolized no further than glutamate. Phosphate-dependent glutaminase activity was present in platelets at 22.3 +/- 6.3 nmol/min/mg protein, a level similar to that seen in lymphocytes and macrophages. Leucodepletion studies excluded a significant contribution of contaminating leucocytes to these measurements. Thrombin stimulation did not increase the rate of glutamine metabolism. Analysis of the rates of glutamine metabolism suggests that it accounts for most of the ammonia produced during PC storage. However, it appears to be relatively insignificant as a metabolic fuel. The role of glutamine metabolism for platelets is uncertain. It may be a vestige of a pathway in the megakaryocyte. The ammonia which it produces may be deleterious for platelets and for patients with liver disease who receive PC infusions.