Adaptative response of alpha- and beta-glucosidase kinetics along the villi of rat self-filling jejunal blind loops

Pathogenesis of the mucosal hyperplasia in self-filling blind loops of rat jejunum: a morphometric study in germ free animals

Bacterial overgrowth and high intraluminal concentrations of deconjugated bile acids are thought to be responsible for mucosal hyperplasia in self-filling blind loops of rat jejunum. To investigate this hypothesis further we have assessed the three dimensional architecture of these loops created in germ free animals without or with di- or mono-association of different bacterial species. It was found that mucosal hyperplasia develops in the absence of any bacterial contamination and that bacterial association does not lead to a more pronounced mucosal proliferation. This implies that other mechanisms provoke this morphological phenomenon. Increased bulk contents in these loops or immunological events are probably the most likely explanation.

Segmental variations in the surface architecture of the normal rat colonic mucosa

A microdissection technique used previously in the small intestine has been adapted for the rat colon in order to determine morphometric data and to calculate surface parameters in various proximal and distal segments (caecum, ascending and descending colon, rectum) of normal colonic mucosa. From the caecum to the rectum there was a gradual significant decrease in the diameter of the middle portions of the crypts, in the number of crypts per unit area and the inner intestinal circumference, as well as in the total mucosal surface per mm intestinal length and the surface of all crypts per unit area. However, there was an increase in the surface of the lining epithelium between the crypts from the caecum to the rectum. These findings are of importance when interpreting alterations in colonic function in terms of segmental changes in the mucosal architecture.

The adaptive response of disaccharidase activities at different sites along the villus epithelium after proximal intestinal resection in the rat. A microdensitometric study of enzyme kinetics

The "in situ" kinetic constants (app. Km and Vmax) of brush border neutral alpha-glucosidase (EC 3.2.1.20) and lactase/beta-glucosidase (EC 3.2.1.21) were determined 4,6 (only alpha-glucosidase), and 12 days after 60% proximal intestinal resection in rat ileum at the villus base and the transition zone between middle and upper villus third by use of a quantitative biochemical analysis of enzymes in tissue sections (section biochemistry). Sham-operated rats served as controls, and the kinetic data (means per rat, time and villus position) were compared (n = 4 animals in each experimental group) first by an overall factorial analysis of variance and thereafter in detail using nonparametric test procedures. Both enzyme activities exhibited a differential response: No changes of lactase/beta-glucosidase kinetics, but a significant decrease in both Vmax- and Km-values of neutral alpha-glucosidase, which was already fully expressed on day 4 after resection and confined to the apical villus region still implying a basoapical increase of Vmax and thus maintaining the normal activity gradient on a lower level. In conclusion, a complex pattern of enzymatic adaptation to proximal intestinal resection ensues in the hyperplastic ileal mucosa which cannot be explained simply in terms of the hypothesis of cellular immaturity.

"In situ"--measurements of protein contents in the brush border region along rat jejunal villi and their correlations with four enzyme activities

In order to quantify the amount of protein in the small intestinal brush border region at different villus sites, cryostat sections of adult rat jejunum were stained with Naphthol Yellow S, Dinitrofluorobenzene and Coomassie Brilliant Blue and the dye deposits were evaluated cytophotometrically. Judged by the absorbance spectra in the tissue sections and the increase in absorbance as a function of the optical pathway (section thickness), Naphthol Yellow S proved to be the most suitable quantitative protein stain. By continuously measuring the absorbance of this dye at lambda 440 nm rectangular to the villus in the longitudinal axis of the enterocytes, a peak was registered in the brush border region which clearly could be differentiated from the apical cytoplasm. The amount of protein in the brush border region was determined at six different positions equally distributed along the villus. In parallel four brush border enzymes (neutral alpha and beta-glucosidase, unspecific alkaline phosphatase and dipeptidylpeptidase IV) were quantified by the same measuring technique in the Vmax-range of their substrate hydrolysis at equivalent villus positions. Their activities were correlated to the amount of protein. The absorbance data both for protein and for enzyme activities were significantly influenced by the villus position. They revealed an increasing gradient from the basal to the apical villus. In an additional analysis of the breadth of the dye deposits at the different measuring positions on the villus, it was shown that this parameter also ran parallel with the absorbance values.

Early changes in brush border disaccharidase kinetics in rat jejunum following subcutaneous administration of tetraiodothyronine: a quantitative histochemical study on villi revealing normal morphology

In order to test the influence of thyroid hormones on small intestine function, adult female Wistar rats were injected daily with either 100 microgram/100 g body weight tetraiodothyronine or placebo. After 12 days, jejunal segments were removed and processed for morphometric analysis of mucosal architecture and quantitative histochemical determinations of the apparent Km- and Vmax-values of lactase/beta-glucosidase and neutral alpha-glucosidase at constant basal and apical measuring positions along the villi. The villus-crypt-architecture was the same in both experimental groups. At the cellular level, however, application of tetraiodothyronine resulted in a marked decrease in the apparent Vmax of lactase/beta-glucosidase at both villus positions, maintaining the normal activity gradient along the villi. In comparison with the controls, a less pronounced but significant reduction in activity was also demonstrated for the neutral alpha-glucosidase. Substrate affinity, however, was only increased for this enzyme, the apparent Km of lactase/beta-glucosidase not being affected by the hormone. The results indicate a direct effect of tetraiodothyronine on jejunal brush border disaccharidases of the rat. The alternative mechanism, an effect mediated by an altered enterocyte turnover is unlikely to occur.