Dietary CHO and stimulation of carbohydrases along villus column of fasted rat jejunum.

Adult rats when fed a high carbohydrate diet of 70% sucrose or glucose for 24 h following a 4-day fast showed increased concentrations of intestinal sucrase-isomaltase (EC 3.2.1.48, EC 3.2.1.10) and maltase-glucoamylase (EC 3.2.1.20) but not lactase-phlorizin hydrolase (EC 3.2.1.23, EC 3.2.1.62). The concentration increases of these enzymes were accompanied by corresponding acceleration of their synthesis rates. Contrary to earlier studies by others, suggesting that upper villus cells in the fasted intestine are unresponsive to stimulation of sucrase activity by refeeding a high-sucrose diet, the concentration increases of both sucrase-isomaltase and maltase-glucoamylase were seen to occur in cells all along the length of the villus column. The earlier studies differed from the present study by basing enzyme assays relative to protein rather than the DNA content of villus cell fractions. We have shown that villus cells increase their protein content severalfold while migrating to villus tip, providing the basis for the difference between earlier and the present findings. Further evidence that stimulation of sucrase-isomaltase and maltase-glucoamylase by high carbohydrate is not restricted to the crypt and lower villus region was obtained by the finding that their synthesis rates appeared to be equally stimulated along the length of the villus column.

Growth and differentiative maturation of the rat enterocyte.

Cells of the intestinal mucosa of the infant and adult rat maintain a pattern of continuous growth, accumulating structural and functional proteins and lipids while migrating the length of the villus column. Cells of jejunal and ileal segments were fractionated sequentially from villus tip to inner crypt and distribution patterns were determined for DNA, total protein, cholesterol, phospholipid, and disaccharidases. Patterns of increasing ratios of protein, lipids, and disaccharidases to DNA were maintained to villus tips, with only slight fall-off of enzymes observed. Distribution profiles of disaccharidases, when computed relative to protein (as seen in previous reports), show distortion of the true cellular distribution pattern of these enzymes as determined by the DNA content of the fractions. Wide variation in cell protein concentrations was evident between jejunal and ileal segments in pre- and postweaned rats. Ileal cells of the suckling rat contained particularly high protein concentrations, which appeared to be largely transitory in nature and related to food intake. Cholesterol and phospholipids were found to be concentrated in the microvillus membrane and account for a significantly large fraction of the cellular content of these lipids.

Hydrogen gas excretion after sucrose gavage in the fasted rat.

The effect of a 3-day fast on the functional ability of the adult rat to hydrolyze and absorb sucrose was determined. The evaluation was based on previous studies which have shown the total amount of hydrogen gas (H2) excreted by the animal to reflect the extent of undigested carbohydrate entering the colon from the small intestine. H2 excretion was measured using a gas chromatographic technique in experimental (72 h fasted) and control (12 h fasted) animals after administration of sucrose by gastric gavage. Total H2 excretion was 3-fold higher in the experimental animals (n = 5) than in the controls (n = 5) (p less than 0.005) indicating a significant increase of sucrose malabsorption in the experimental animals. Administration of a second dose of sucrose 8 to 9 h after the first dose (refeeding) resulted in markedly decreased malabsorption relative to the first administration in both experimental (n = 2) and control (n = 2) animals. These results suggest that a 3-day fast markedly impairs the ability of the intestine to hydrolyze and absorb sucrose and that refeeding rapidly restores the ability to utilize this substrate. H2 excretion was similar between experimental and control animals after the administration of lactulose, a nonabsorbed and nondigested carbohydrate, suggesting that the observed results of the sucrose studies were independent of any possible changes in the intestinal microflora.