THE ROLE OF GLUTAMINE IN THE IMMUNE-SYSTEM AND IN INTESTINAL FUNCTIONIN CATABOLIC STATES

Glutamine is designated a non-essential amino acid: however, evidence is accumulating that glutamine becomes essential when catabolic condit ions prevail. It has been established that glutamine is an important f uel for lymphocytes and macrophages, even when resting. Plasma and mus cle glutamine concentrations are decreased after trauma such as burns, major surgery, and in sepsis. The effectiveness of the immune system is decreased after trauma: this may be due, in part, to the decrease i n plasma glutamine concentrations. Most studies on sepsis in humans ha ve shown plasma glutamine concentrations to be decreased: this may be due to an increased rate of utilization of glutamine by lymphocytes an d macrophages during proliferation or phagocytosis. In contrast, sever al studies on rats show increased plasma glutamine levels in sepsis. A species difference in the way in which glutamine is metabolised could be the main reason for the conflicting results. Other contributory fa ctors could be diurnal variation and timing of sample collection. A su bstantial amount of dietary glutamine is taken up by intestinal cells. When the supply of glutamine via the diet is decreased, glutamine is taken up from the circulation by the intestine. In total parenteral nu trition (TPN) sepsis can sometimes occur because the gut is ''rested'' , leading to villous atrophy and increased gut mucosal barrier permeab ility. There is now a move towards the use of enteral nutrition in pre ference to TPN. Provision of exogenous glutamine has had beneficial ef fects in humans and animals, particularly in improving intestinal func tion. The safety and efficacy of glutamine administration to humans is discussed in detail.