Glutamine and alanine metabolism in lungs of septic rats

Abstract

1. The metabolism of glutamine and alanine in the lung was studied in rats made septic by a caecal ligation and puncture technique. 2. The blood glucose concentration was not significantly different in septic rats, but blood pyruvate, lactate, glutamine and alanine concentrations were markedly increased as compared with sham-operated rats. Conversely, blood ketone body and plasma cholesterol concentrations were significantly decreased in septic rats. Both plasma insulin and plasma glucagon concentrations were markedly elevated in response to sepsis. Sepsis resulted in a negative nitrogen balance. 3. Sepsis increased the rates of production of glutamine (52.5%, P <0.001), alanine (38.9%, P <0.001) and glutamate (48.6%, P <0.001) by lung slices incubated in vitro. 4. Sepsis increased lung blood flow by 27.6% (P <0.05). Blood flow and arteriovenous concentration difference measurement across the lung of septic rats showed an increase in the net exchange rates of glutamine (142.5%, P <0.001), alanine (129.4%, P <0.001), glutamate (100.9%, P <0.001) and ammonia (138.0%, P <0.001) as compared with sham-operated control rats. 5. Sepsis produced significant decreases in the lung concentrations of glutamine (36.8%), glutamate (20.8%), 2-oxoglutarate (64.8%) and AMP (18.3%). The lung concentrations of alanine (95.9%), ammonia (67.7%) and pyruvate (89.7%) were increased. 6. The maximal activities of glutamine synthetase (20.4%, P <0.05), phosphate-dependent glutaminase (18.9%, P <0.05) and alanine aminotransferase (25.5%, P <0.05) were increased, but there was no marked change in that of glutamate dehydrogenase, in the lungs of septic rats. 7. It is concluded that there are enhanced rates of production of glutamine and alanine from lungs of septic rats (both in vitro and in vivo). This may be due to changes in efflux and/or increased intracellular biosynthesis of both glutamine and alanine; these suggestions are discussed.