Regulation of rat proximal intestinal glycolytic enzyme activity by ileal perfusion with glucose.

Specific activities of the glycolytic enzymes fructose-1-phosphate aldolase, fructose-1,6-diphophate aldolase, and pyruvate kinase, are higher in rat duodenum and jejunum than in ileum. Whether this gradient reflects the failure of dietary sugars to reach the ileum in high concentrations is unknown. Rats were first fed a carbohydrate-free diet for 3 days, which virtually removed the proximal-distal gradient of enzyme specific activities. Twenty percent glucose was then perfused directly into either the duodenum or the ileum for 3 days. Both proximal and distal glucose perfusion restored the normal gradient of all three enzymes. Ileal pyruvate kinase was also increased by ileal glucose perfusion, but ileal aldolases were no higher after distal perfusion than after duodenal perfusion. The low ileal aldolase levels normally found in fed rats therefore are an intrinsic property of distal intestine and are not due to failure of dietary sugar to reach this portion of the gut. Furthermore, adaptation of duodenal and jejunal glycolytic enzymes to ileal glucose perfusion suggests a humoral and/or neural mechanism rather than a direct local luminal effect of the sugar itself.

Regional variation in glycolytic enzyme adaptation to dietary sugars in rat small intestine.

This investigation evaluated the adaptive response of the glycolytic enzymes, fructose-1-phosphate aldolase, fructose-1, 6-diphosphate aldolase, and pyruvate kinase, to dietary sugars throughout the small intestine. In addition, the effect of prior diet on this adaptive response and on the enzyme distribution pattern along the small intestine was studied. Rats were fed 40% glucose, 68% sucrose or carbohydrate-free diets for 6 days (baseline diet), followed by one of three isocaloric test diets (40% glucose, 68% sucrose or carbohydrate-free for 3 days. In other groups of tats isocaloric diets of 68% glucose, 68% fructose or 34% glucose + 34% fructose, fed for 4 days, were compared. Enzymes were assayed in the mucosa of the duodenum (D),and in 5 equal (by length) segments from the Ligament of Treitz to the ileocecal valve (J1, J2, J3, I1 and I2). Enzyme specific activities were significantly higher in the proximal (D-J1-J2) than distal segments (J3-I1-I2) on all diets (P smaller than 0.001). Enzyme activities after test diet periods were determined only by the test diet, and were independent of the baseline diet for all segments. The 68% carbohydrate diets increased enzyme activities significantly more (P smaller than 0.001) than the 40% glucose or carbohydrate free diets, in all segments. On the 40% glucose diet, activities were significantly higher (P smaller than 0.05) than on the carbohydrate free diet in D and J1, but not distally. The data suggest that there is an intrinsic gradient of enzyme activity from the proximal to the distal small intestine which persists despite dietary manipulation, and that all segments of the small bowel show adaptive increases to dietary sugars.