Metabolism and transport of glutamine and glucose in vascularly perfused small intestine of the rat

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Abstract
The metabolism and transport of glutamine and glucose were investigated in a preparation of rat small intestine perfused through the vascular bed in vitro and in situ. With glucose (7.5 mM) or glutamine (4.5 mM) in the lumen, .apprx. 40% of the substrate taken up appeared unchanged on the vascular side. When glutamine (1.5 mM) was also added to the vascular perfusate, metabolism of glutamine was increased and there was uptake of glutamine from both the vascular bed and lumen. Orientation of substrate (vascular bed or lumen) influenced the value of alanine production/glutamine utilization and lactate production/glucose utilization. Deprivation of food and metabolic acidosis had no effect upon the utilization of glutamine by unit length of jejunum. In fed rats, glutamine utilization was 44% of glucose utilization, but in rats deprived of food it was 112% of glucose utilization. Glucose utilization and lactate production were not significantly altered by the presence of glutamine in the vascular bed or lumen. With glucose only in the vascular perfusate, glucose utilization was the same in jejunum and ileu. Glutamine metabolism in the ileum was 28% lower than in the jejunum. Glutamine utilization was dependent on the concentration of glutamine in the vascular perfusate, but was not significantly affected by the absence of glucose. Results were discussed in relation to the role of intestinal glutamine metabolism and with respect to some problems of the transepithelial movement of substrates that were both transported and metabolized.