Glycosylation of lactase-phlorizin hydrolase in rat small intestine during development

Age-specific changes in glycosylation of rat intestinal lactase-phlorizin hydrolase were analyzed using enzyme immunoprecipitated from microvillus membranes of suckling, weaning, and adult rats, and carbohydrate moieties were examined by lectin affinity binding, metabolic labeling, and neuraminidase treatment. Lectin binding indicated the presence of N-linked and O-linked oligosaccharide chains containing mannose and galactose throughout development. An age-dependent shift in sialic acid and fucose was seen during the period of weaning; no fucose was detectable in lactase-phlorizin hydrolase until after the rats were 20 days of age, whereas sialic acid was reduced in adult lactase-phlorizin hydrolase. The presence of sialic acid in suckling intestines and fucose in adult was confirmed by metabolic labeling with appropriate radioactive precursors. Sodium dodecyl phosphate-polyacrylamide gel electrophoresis analysis of immunoprecipitated lactase-phlorizin hydrolase from the proximal and mid small intestine showed two bands of approximately 220 and 130 kilodaltons in all age groups. In the distal part of the adult small intestine, lactase-phlorizin hydrolase appeared as two bands of similar size to those found in the proximal and mid portions. In contrast, during the suckling and weaning periods, these distal bands were approximately 225 and 135 kilodaltons. [35S]-methionine labeling and fluorography of neonatal intestines confirmed these observations. The size difference between proximal and distal small intestines was virtually eliminated by neuraminidase treatment. These data indicate that the core structure of microvillus membrane lactase-phlorizin hydrolase, consisting of both N-linked and O-linked oligosaccharides, remains constant during development, although terminal sugars shift from predominantly sialic acid during the suckling period to fucose in adulthood. This alteration in glycosylation of the protein occurs in a different pattern from the postweaning decline in lactase specific activity. Consequently, age-dependent changes in glycosylation cannot account for the decrease in lactase-phlorizin hydrolase-specific activity observed during development.     

Retinoid metabolism in the small intestine during development of liver cirrhosis

Background and Aims:  Retinoids are important mediators of cellular differentiation and proliferation in various epithelia of the body including the small intestine. Though alterations in intestinal epithelial cell proliferation have been noted in liver cirrhosis, mechanisms involved in the process are not well understood. This study examined the levels of various retinoids and retinoid-metabolizing enzymes in the small intestine during development of liver cirrhosis.
Methods:  Four groups of animals were used (control, phenobarbitone control, thioacetamide and carbon tetrachloride treatment). Twice-weekly intragastric or i.p. administration of carbon tetrachloride or thioacetamide, respectively, produced liver cirrhosis after 3 months, which was confirmed through histology and serum markers. Retinoid levels were measured by high-performance liquid chromatography.
Results:  A decrease in the levels of retinal, retinoic acid and retinol was evident in the intestine by 3 months, when cirrhosis was evident histologically, and these remained low until 6 months. A decrease in the activities of retinaldehyde oxidase, retinaldehyde reductase and retinol dehydrogenase was also seen in intestine from cirrhotic rats.
Conclusion:  These results suggest that altered retinoid metabolism in the intestine of cirrhotic rats might have an influence on changes in intestinal epithelial cell differentiation, seen in liver cirrhosis.     

Distribution of disaccharidases, alkaline phosphatase, and some intracellular enzymes along the human small intestine.

The longitudinal distribution of various enzymes along the human small intestine was studied by analysis of biopsies from different parts of the small intestine, obtained from 13 patients during shunt-operation for severe obesity. Alkaline phosphatase and 3 glycolytic enzyme activities studied were rather uniformly distributed along the small intestine. Acid beta-galactosidase and hetero beta-galactosidase activities were highest in the proximal small intestine with a gradual decline throughout the intestine. The activity in the distal ileum was about half of the maximum activity. Maltase, isomaltase, sucrase, and trehalase activity had a broad maximum in the proximal and middle small intestine with a rather sharp decrease in the distal ileum. Lactase activity had a more pronounced maximum in the middle intestine with a pronounced decrease towards the proximal and distal ends. The disaccharidase activities in surgical biopsies taken 5 cm distal to the ligament of Treitz were about 10% higher than in peroral biopsies taken just at the ligament.     

Influence of remote cancer and obesity on, and distribution of mucosal enzymes in, the upper small intestine

A series of mucosal enzymes were estimated by analysis of homogenized biopsy specimens from the lower duodenal flexure, obtained from 10 large-bowel carcinoma patients, 15 patients with morbid obesity, and 15 controls. In 11 subjects the distribution along the upper small intestine was determined. The activities of the brush border enzymes lactase (p less than 0.01), neutral-alpha-glucosidase (p less than 0.01), and alkaline phosphatase (p less than 0.05) were significantly lower in the large-bowel carcinoma patients than in the controls. In obese subjects significantly lower activities (p less than 0.05) were demonstrated for the basolateral membrane enzyme 5'-nucleotidase and the lysosomal enzymes N-acetyl-beta-D-glucosaminidase and acid beta-glucuronidase, when compared with those in controls. Compared with the enzyme levels of the duodenal bulb, significantly higher activities of a series of enzymes were demonstrated at both the lower duodenal flexure and the angle of Treitz.     

Effect of thyroidectomy on the activity of alpha-glucosidases and acid hydrolases in the small intestine of rats during weaning.

Adrenalectomy performed on 14-day-old rats delayed the usual increase of sucrase and maltase activity as well as the decrease of acid beta-galactosidase, beta-glucuroindase and N-acetyl-beta-glucosaminidase activity during the third postnatal week. Since these changes were only delayed, the role of the thyroid was explored. Thyroidectomy performed simultaneously with adrenalectomy on 14-day-old rats did not influence the increase in body weight and growth of the small intestine (already slowed down by adrenalectomy), but caused a further substantial delay in the maturation of the enzyme profile of the small intestine. Our results indicate that the thyroid is involved in regulation of the hydrolases studied.     

Morphological properties and residual strain along the small intestine in rats

AIM: Residual stress and strain are important for gastrointestinal function and relate to the geometric configuration, the loading conditions and the zero-stress state of the gastrointestinal tract. The purpose of this project is to provide morphometric data and residual strains for the rat small intestine ( n =11). METHODS: To approach the no-load state, the intestine was surgically excised, transferred to an organ bath and cut transversely into short ring-shaped segments. Each ring was cut radially for obtaining the zero-stress state. The residual stress can be characterised by an opening angle. The strain difference between the zero-stress state and the no-load state is called residual strain. RESULTS: Large morphometric variations were found along the small intestine. The wall thickness was highest in the proximal duodenum and decreased in distal direction along the axis of the small intestine (P<0.001). The circumferential length of the inner and outer surfaces decreased rapidly along the length of duodenum by 30-50% (P<0.001). The wall area and lumen area showed a similar pattern (P<0.001). In zero-stress state the rings always opened up after making the cut. The experiments resulted in larger inner circumferential length and smaller outer circumferential length when compared to the no-load state. The wall thickness and wall area did not differ between the no-load and zero-stress state. The opening angle and tangent rotation angle increased along the length of the duodenum and had its highest value 30% down the intestine. Further down the intestine it decreased again (P<0.001). The serosal residual strain was tensile with the highest value close to the ligament of Treitz (P<0.001). The mucosal residual strain was compressive in all segments of the small intestine with average values between -0.25 and -0.4 and with the lowest values close to the ligament of Treitz (P<0.001). CONCLUSION: Axial variation in morphometric properties and residual strains were found in the small intestine. Existence of large residual strains indicates that the zero-stress state must be considered in future biomechanical studies in the gastrointestinal tract.     

Effect of dietary fat on the distribution of mucosal mass and cell proliferation along the small intestine.

This study investigated how substitution of long chain triglycerides for glucose in a mixed diet affects the overall small intestinal mucosal mass and the distribution of mucosal mass and cell proliferation along the small intestine. Four groups of eight female Wistar rats (180-200 g) were isocalorically fed mixed diets containing the essential fatty acid rich oil Efamol substituted for glucose at concentrations of 1.2%, 10%, 25%, and 50% total calories for 20 to 23 days. The small intestine was divided into three equal length segments and whole gut weights, mucosal weights, protein and DNA determined. Cell proliferation was estimated from the two hour accumulation of vincristine arrested metaphases in microdissected crypts at points 0%, 17%, 33%, 50%, 66%, and 100% small intestinal length. There were no differences between groups in parameters of overall small intestinal or distal segment mucosal mass. With increasing levels of fat, however, there was a significant trend for the mucosal mass of the proximal segment to fall and that of the middle segment to rise. The pattern of two hour metaphase accumulation reflected these changes. These regional changes in mucosal mass and cell proliferation may reflect differences in the sites of absorption of fat and glucose.     

Effect of breast milk and weaning on epithelial growth of the small intestine in humans

Breast feeding and weaning are important physiologically significant luminal events that influence the growth of the small intestine in humans. A variety of factors including genetic preprogramming, systemic and local hormones, and permissive factors contribute and modulate intestinal growth. Here, we offer a view that integrates some of these factors, especially those relating to breast feeding and weaning.     

Accumulation of abundant messenger ribonucleic acids during postnatal development of mouse small intestine

To describe the differentiation of the small bowel at the molecular level, intestinal messenger ribonucleic acids (mRNAs) from mice at different stages of fetal and postnatal development were investigated. On the basis of cell-free translation and complementary deoxyribonucleic acid cloning experiments, abundant mRNAs coding for small polypeptides of 6-12 kilodaltons (low-molecular-weight mRNAs) were found in adult small intestine but not in the fetal gut. These developmentally regulated low-molecular-weight mRNAs are uniquely abundant in jejunum and ileum of adult mice, but they are absent or occur only at low levels in the duodenum, colon, stomach, and all other mouse organs examined. Low-molecular-weight mRNAs begin accumulating in the small bowel at approximately 3 wk of age, coinciding with weaning and with profound changes in intestinal differentiation. One complementary deoxyribonucleic acid clone of a low-molecular-weight mRNA (asb4/134) is specific to the distal small bowel, specifically accumulates at weaning, and hybridizes to RNA from mouse testis and brain at approximately 2%-5% of the intestinal level. Low-molecular-weight mRNA sequences may provide important markers of intestinal differentiation at the genetic level, leading to a better understanding of the factors that contribute to its postnatal maturation.     

Pyrimidine biosynthetic enzymes in rat intestine after small bowel resection.

After small bowel resection in the rat, mucosal hyperplasia and an increase in nucleic acid synthesis and cell proliferation occur in remaining small intestine. Male Sprague-Dawley rate underwent resection of 50 cm of proximal or distal intestine or sham operation. One month and 6 months after surgery, aspartate transcarbamylase, dihydroorotase, and uridine kinase were assayed in whole mucosa, and in some instances, in crypt mucosa ffrom the remaining intestinal segment. In control bowel, enzyme activity was significantly greater proximal compared with distal segments. One month after proximal or distal resection, mucosal enzyme activity per cm of gut was greater in the remnant bowel compared with controls. There was no such difference at 6 months. Specific enzyme activity of whole mucosa did not increase after resection because the assay was influenced by the disproportionately large contribution of villous protein. Specific enzyme activity (including thymidine kinase) of isolated crypt mucosa was significantly increased 1 month after distal resection. In addition, [3H]thymidine uptake into DNA of crypt mucosa from proximal remnants was also significantly increased. These results indicate that after small bowel resection, the enzymes of pryimidine biosynthesis increase in remaining bowel and parallel the accelerated rate of cell proliferation.     

Intestinal slow waves: Decrease in propagation velocity along upper small intestine

Electrical activity was recorded from platinum electrodes permanently implanted on dog small intestine. Dogs were unanesthetized, healthy, and cooperative when studied. Slow waves appeared to decelerate as they passed along the upper small intestine. Their velocity was about 15 cm./sec., 24 cm. above the ligament of Treitz, but only 3 cm./sec., 24 cm. below the ligament of Treitz. This decrease in velocity occurred over a region of upper small intestine in which the frequency of slow waves remained essentially constant.This paper includes a portion of the work presented in the Doctoral Dissertation of Doctor McCoy, entitled Studies of Electrical Activity in the Small Intestine of the Dog.     

Immunoglobulin-containing cells in the small intestine during acute enteritis

Jejunal mucosal biopsies were obtained from 13 patients with acute enteritis. Ten patients were examined again after recovery. Quantitative analysis of the findings in immunofluorescence microscopy showed a significant increase of IgA- and IgM-containing cells during acute enteritis. After recovery the number of immunoglobulin-containing cells and their distribution within the different immunoglobulin classes were within normal limits.