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

Abstract

1. 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. 2. With glucose (7.5mm) or glutamine (4.5mm) in the lumen, approx. 40% of the substrate taken up appears unchanged on the vascular side. When glutamine (1.5mm) is also added to the vascular perfusate, metabolism of glutamine is increased and there is uptake of glutamine from both the vascular bed and lumen. Orientation of substrate (vascular bed or lumen) influences the value of alanine production/glutamine utilization and lactate production/glucose utilization. 3. Deprivation of food and metabolic acidosis have no effect upon the utilization of glutamine by unit length of jejunum. In fed rats, glutamine utilization is 44% of glucose utilization, but in rats deprived of food it is 112% of glucose utilization. 4. Glucose utilization and lactate production are not significantly altered by the presence of glutamine in the vascular bed or lumen. 5. With glucose only in the vascular perfusate, glucose utilization is the same in jejunum and ileum. Glutamine metabolism in the ileum is 28% lower than in the jejunum. 6. Glutamine utilization is dependent on the concentration of glutamine in the vascular perfusate, but is not significantly affected by the absence of glucose. 7. Results are discussed in relation to the role of intestinal glutamine metabolism and with respect to some problems of the transepithelial movement of substrates that are both transported and metabolized.

Fuel utilization in colonocytes of the rat

“…However, the oxidation of fatty acids did not contribute significantly to energy formation even in the starved state (Hanson & Parsons, 1977Windmueller &Spaeth, 1978Watford et al, 1979;Windmueller, 1984). In a similar manner to other rapidly dividing cells (e.g.…”

“…Themajor end-products of glutamine metabolism in colonocytes are glutamate, aspartate, alanine and ammonia (Table 1). This is in contrast with the cells of the small intestine, which produce alanine rather than aspartate (Hanson & Parsons, 1977;Watford et al, 1979Watford et al, , 1984Porteous, 1980), and lymphocytes or thymocytes, in which aspartate production predominates (Ardawi & Newsholme, 1983a, 1984aBrand et al, 1984). Of the glutamine utilized by colonocytes, ammonia production accounted for 38% of the glutamine nitrogen, which, since the glutaminase reaction produces ammonia, suggests that glutamate is metabolized via transaminase reactions rather than by glutamate dehydrogenase.…”

“…Starvation of the rat is known to decrease by almost 50% the rate of glucose utilization by the small intestine (Hanson & Parsons, 1977); incubated coloncytes isolated from 48 h-starved rats exhibited a decrease in the rates of glucose utilization and lactate production (results not shown), which may be explained in part by decreases in activities of hexokinase and 6-phosphofructokinase and increases in those of glucose-6-phosphatase and fructose bisphosphatase (Table 3).…”

Fuel selection in intestinal cells

“…Calculations from succinate-C02 ratio ( 14C02 from [ 1 ,4-14C]succinate: l4Co2 from [2,3-14C]succinate) or from acetate-C02 ratio (14C02 from [l-14C]acetate: I4CO2 from [2-14C]acetate) in the presence of glutamine predicts that glutamine molecules entering the tricarboxylic acid cycle have a low probability of remaining in the cycle for a complete turn (Mallet et al 1986b;Fleming & Kight, 1994 . Because the addition of 3-mercaptopicolinate, an inhibitor of PEPCK, has no effect on glutamine oxidation, PEPCK plus pyruvate kinase may play only a minor role in the second decarboxylation of glutamine-C and the generation of pyruvate and alanine (Hanson & Parsons, 1977;Watford et al 1979;Watford & Tatro, 1989;Watford, 1994). Similarly, the step catalysed by oxaloacetate decarboxylase probably does not make a significant contribution to the decarboxylation of glutamine.…”

Aerobic Glycolysis: Meeting the Metabolic Requirements of Cell Proliferation

“…In proliferating cells, glutamine carbons are converted to amino acids, TCA cycle intermediates, lactate, and CO 2 (Hanson & Parsons 1977, Lanks 1987, Newsholme et al 1985a, Watford et al 1979. Figure 2 provides an overall schematic for contributions of glucose and glutamine to biomass, lactate, and CO 2 .…”