Stereological studies on the small intestinal epithelium of the rat. 1. The absorptive cells of the normal duodenum and jejunum

Asymmetric mucosal structure, mesenteric versus antimesenteric, in mouse, rat, and human small intestines

The morphology of the small intestinal mucosa is reflected by the degree of stimuli. Previous studies have come to different conclusion about whether the mucosa is equally symmetrical. The aim of the study is to investigate whether there are structural differences in the mesenteric versus antimesenteric mucosa in mice, rats, and humans. Jejunal biopsies from mice and rats were saved. Samples from human small intestine were obtained from patients undergoing Roux-en-Y gastric bypass surgery. Fixed samples were used to morphologically evaluate villus height and enlargement factor due to villi. The number of goblet cells, mast cells, enteroendocrine cells, and Paneth cells were histologically analyzed in the villus structure. Cell turnover was analyzed by Ki-67 staining. There was a significant increased villi height and villus enlargement factor antimesenterically in mice, rats, and human small intestines. The distribution of goblet cells, mast cells, and Paneth cells were equal while the number of enteroendocrine cells was increased antimesenteric in the human samples. The crypt mitotic activity was almost 20% higher in the antimesenteric part of jejunum. In summary we found longer villi, greater surface enlargement, and increased number of enteroendocrine cells as well as increased cell turnover antimesenterically. These differences may be of importance in understanding normal gastrointestinal physiology in health and disease.

Surface area assessment of the murine intestinal tract as a prerequisite for oral dose translation from mouse to man

In many pharmacological and toxicological studies knowledge about the intestinal absorption, which is dependent upon the surface area of absorptive epithelia, is indispensible. Although mice are often used in such preclinical studies, very few quantitative data about their intestinal surface area are available. Especially for locally acting candidate drugs in development, this information is crucial for dose translation towards humans. Therefore, the surface area of the intestinal tract of CD-1™ IGS mice was assessed in the present study. The intestinal tracts of 12 mice were collected after euthanasia. From six animals, histological sections from the duodenum, jejunum, ileum, caecum and colon-rectum were made according to common stereological principles. Using these sections, the volumes and surface areas of each intestinal segment were estimated applying stereological counting procedures. In the other six animals, the density and surface area of the microvilli present in each intestinal segment were determined by means of scanning and transmission electron microscopy to assess the increase of the intestinal surface area attributable to the presence of microvilli. The mean total volume and surface area of the intestinal tract were 1.34 cm3 and 1.41 m2, respectively. The relative intestinal surface area (intestinal surface area divided by the body surface area) was 119. The relative intestinal surface area of mice is very similar to that of humans. The results of this study are important for the appropriate dose translation of candidate therapeutic compounds in drug development from mouse to humans.

Morphometric study of the guinea pig small intestine during development

The mucosal surface area of the guinea pig duodenum, jejunum, and ileum was determined during development, in three age groups: 1-day-old and 2- and 12-week-old animals. The morphometric analysis was performed at three magnification levels. The nominal surface area was determined at the macroscopic level, from intestinal length and perimeter. Villus and microvillus amplification factors were estimated at light-microscopic and transmission electron-microscopic levels, respectively. We found: (1) an increase in the nominal surface area that is maximal in the ileum (7.7-fold); (2) an increase in the villus amplification factor in the duodenum (1.4-fold) and a decline in the jejunum and ileum (0.8-fold), although in the jejunum villus dimensions rise; and (3) a similar increase in the microvillus amplification factor in the three segments (1.1- to 1.4-fold). In conclusion, the total mucosal surface area increased from day 1 to week 12, by 3-fold in the duodenum and jejunum and by 8-fold in the ileum. Regionally, the jejunum shows the largest mucosal surface area, followed by the ileum, and, finally, the duodenum.

Evaluation of viability of excised rat intestinal segments in the Ussing chamber: investigation of morphology, electrical parameters, and permeability characteristics

PURPOSE

To clarify relations between alterations in electrical and permeability data with time and to elaborate accompanying structural changes of intestinal segments in Ussing chamber experiments.

METHODS

Excised intestinal segments from the rat were studied in a modified Ussing chamber. Experiments were run up to 180 minutes during which the electrical parameters, PD, SCC, and R, were measured and the permeability coefficients (Papp) of mannitol and propranolol were determined. Each segment was observed under the light microscope for morphological evaluation.

RESULTS

PD and SCC values showed a decrease for most segments while the R values remained steady throughout the experiment. The Papp for propranolol increased aborally to the small intestine. For mannitol, the reversed was observed. In some cases, there was a time-dependent change in permeability for these marker molecules. The main morphological changes observed were a decreased nucleo-apical distance, decreased villi amplification factor, initial edema, cell sloughing, and epithelial restitution.

CONCLUSIONS

The time-dependent changes in permeability coefficients of mannitol and propranolol are suggested to be related to changes in electrical parameters and morphological alterations. Presented data illustrates the importance of information regarding time-dependent structural changes for correct interpretation of permeability data.

Epidermal growth factor and human growth hormone accelerate adaptation after massive enterectomy in an additive, nutrient-dependent, and site-specific fashion

BACKGROUND

After massive enterectomy (ME), remnant intestine undergoes compensatory adaptation. Epidermal growth factor (EGF) and human growth hormone (hGH) have each been shown to enhance total length small intestine nutrient transport after ME. This study aims to determine the differential effects of EGF and hGH on proximal and distal small intestinal remnants after ME.

METHODS

New Zealand white rabbits underwent 70% mid-jejunoileal resection. After 1 week, animals received hGH (0.2 mg/kg/day), EGF (1.5 micrograms/kg/hr), hGH + EGF, or vehicle (equal volume) for 7 days. Sodium-dependent uptake of glucose, glutamine, alanine, leucine, and arginine into brush border membrane vesicles was quantitated. Serum insulin-like growth factor-I concentrations as well as proximal and distal villus and microvillus heights were measured. IGF binding protein-3 and -4 mRNA expression was determined in full-thickness proximal and distal gut remnants.

RESULTS

Concomitant hGH and EGF treatment up-regulates glucose (100%), glutamine (80%), and leucine (60%) transport in the proximal remnant; alanine (150%) and arginine (400%) transport in the distal remnant; and microvillus height (25% to 35%) both proximally and distally. Serum IGF-I levels and gross villus heights were not different among groups.

CONCLUSIONS

Co-infusion of hGH and EGF accelerates intestinal adaptation after ME in an additive, nutrient-dependent, and site-specific fashion via enhanced nutrient transport as well as microvillus hypertrophy.

Cell apical surface area in enterocytes from chicken small and large intestine during development

The absorptive surface of epithelial cells from chicken small and large intestine was studied at the day of hatch (1 d group) and at 2 and 6 wk after hatch. The segments considered were duodenum, jejunum, ileum, cecum (proximal, medial, and distal regions), and rectum. The length, diameter, and density of microvilli as well as cell apical diameter were measured in tip-villous enterocytes by transmission electron microscopy. The results obtained showed that during development: 1) microvillus length remained constant in duodenum and jejunum and decreased in the other segments; 2) microvillus diameter increased only in the jejunum and the rectum; 3) microvillus density increased in duodenum, ileum, distal cecum, and rectum (especially from 1 d to 2 wk) and did not change in the other segments; 4) cell apical diameter did not change; 5) apical surface area increased both in the duodenum (2nd to 6th wk) and in the jejunum (1 d to 2 wk) but did not change in the ileum. In the proximal-medial cecum and in the rectum there was a decrease in apical surface, whereas no changes were observed in distal cecum. Results indicated that microvillus length and density are the variables that best explain the changes observed in apical surface that occurred during development.

Oat bran, rye bran, and soybean hull increase goblet cell volume density in the small intestine of the golden hamster. A histochemical and stereologic light-microscopic study

Small-intestinal morphology, particularly the amount of goblet cells, was studied in Syrian golden hamsters fed either a low-fibre (0.5% fibre) diet or the same diet supplemented with oat bran, rye bran, or soybean hull (12% fibre) during 6 weeks. All fibre diets increased the density of goblet cell volume to epithelial volume and to villus volume in the ileum and to some extent in the jejunum and also the number of goblet cells related to surface traces of villi both in the proximal and distal small intestine. The weight of the small intestine and the circumference and the volume of the intestinal wall in the ileum were greater in the rye bran diet group as compared with all the other groups, suggesting hyperplasia. These results suggest that oat bran, rye bran, and soybean hull supplementation might result in higher goblet cell secretory activity in both the proximal and distal small intestine of hamsters. The various fibre sources influenced the small-intestinal wall differently.

Morphometric analysis of the effects of antineoplastic drugs on mucosa of normal ileum and ileal anastomoses in rats

Antineoplastic agents affect the healing of intestinal anastomoses. They often induce anorexia and diarrhea, possibly caused by morphological changes in the small intestinal mucosa. These changes were evaluated in the rat ileum. Animals in group I underwent only intestinal surgery while those in groups II and III underwent surgery on the third day of a 5-day course with cisplatin (in two different doses), bleomycin, and 5-fluorouracil. The parameters were: number of mitoses in crypts, crypt depth, villus height, width, and contour length, measured in the mucosa of primarily resected segments of the ileum and of the anastomotic area. Surgery yields an increased crypt depth and villus length in the anastomotic area without changing villus width. The changes in intestinal crypts precede those in villi. Antineoplastic drugs decrease crypt mitotic rate, villus height, width, and contour length. After cessation of antineoplastic chemotherapy mitotic activity increases. The shallower and shorter villi increase in width and length resulting in an increased villus contour length and area. A linear relation exists between villus contour length and villus height and width. Thus, antineoplastic polychemotherapy, dose-dependently, reduces and surgical trauma increases intestinal proliferative activity. However, the morphologic changes do not unequivocally explain possible metabolic disturbances causing retarded intestinal wound healing.

Striated brush border of intestinal absorptive epithelial cells: stereological studies on microvillous morphology in different adaptive states

Different regions of small bowel were examined in five groups of rats in three separate experiments. The effects on mucosal morphology of position along the bowel, induced hypoproliferation (due to fasting), and induced hyperproliferation (due to streptozotocin diabetes) were investigated. Intestines fixed by in situ perfusion with buffered glutaraldehyde were sampled by strictly randomised procedures. Pieces of tissue from segments of roughly equal length were processed for electron microscopy and embedded in resin. Complete transverse sections were cut for light microscopy and estimates of villous surface areas were obtained by stereological methods devised for the purpose. Ultrathin sections from random sectors of the same tissue blocks were sampled systematically to obtain micrographs of the villous surface. These were analysed for quantitative information about microvilli (length, diameter, surface area, and number). Structural quantities from individual segments were pooled to provide values for the entire small bowel. Significant regional differences in villous and microvillous dimensions were found in all groups. The numbers of microvilli per bowel were remarkably constant in all control groups. Other variables were estimated reproducibly in rats of the same sex, strain, and average body weight. Effective absorptive surfaces did not show a linear gradient but tended to peak in middle segments. Neither fasting nor induced diabetes altered the mean length, diameter, or packing density of microvilli. However, surfaces due to villi and microvilli altered commensurately during fasting and induced diabetes. Therefore cell number seems to be the key quantity for determining villous and microvillous surface areas. The findings are discussed in the context of kinetic, biochemical, and physiological changes found in different adaptive states.

The development of the fetal rat intestine and its reaction to maternal diabetes. I. Morphometrical analysis in normal conditions

In rodents, the fetal intestine develops rapidly during the last 5 days of gestation. The present investigation describes the events which occur in the duodenum, jejunum and ileum of fetal Wistar rat from day 16.5 to 21.5. The first villi and microvilli as well as endocrine cells already appear at 17.5 days in the duodenal mucosae. Goblet cells are detected at 18.5 days. The structure of the intestinal mucosa at 21.5 days is similar to that of adults. The evolution was quantified by morphometric analysis. The external and inner circumference, the length of the villi profile and the increased absorption area due to the villi profile were measured. We demonstrated that the total enlargement of the luminal surface area due to the villi and the microvilli in the duodenum of the fetus at 21.5 days is similar to that in the adult duodenum. This morphometric analysis could be used to detect possible disturbances in the development of the fetal intestine.

Adaptation of intestinal morphology in the temperature-acclimated carp, Cyprinus carpio L

The effects of temperature and photoperiod acclimation upon the morphology of carp intestinal mucosa have been studied using morphometric techniques. Carp intestine showed an absence of anatomical regionalisation. There was a gradual reduction in the dimensions of villi along the tract. The decrease in the dimensions of the villi was greatest in the anterior half. Temperature acclimation had no effect on intestinal-somatic indices. Acclimation to 10 degrees C or 30 degrees C resulted in large differences in the dimensions of villi. Cold acclimation produced significant increases in mean villus height and breadth along the entire intestine. These villus shape changes resulted in a 58% increase in total mucosal surface area and a 102% increase in total volume of villi in cold-acclimated fish relative to warm-acclimated fish. Surface area of the unmodified intestinal tube increased with cold acclimation by 28%. The total number of villi remained unchanged by thermal acclimation. Because normalisation to a nominal surface area does not take account of the possibility of differentially developed mucosal surfaces in differently acclimated animals, experiments comparing transepithelial transport rates of differently-acclimated fish, using unstripped preparations, overestimates the differences in area-specific transport capacity.

Quantitative alterations in the structural development of jejunal absorptive epithelial cells and their subcellular organelles in protein-energy-malnourished rats: a stereologic analysis

The effect of protein-energy malnutrition (PEM) on the structural development of rat jejunal absorptive epithelial cells was evaluated. Stereologic characteristics of jejunal histologic subcompartments, epithelial cell surfaces and volumes, and volumes of key subcellular organelles (nuclei, mitochondria, Golgi apparatus, lysosomes) in crypt and villus mid and tip cells were determined by morphometric analysis of light and electron micrographs in well-nourished rats and rats with PEM. In rats with PEM there were developmental alterations in cells migrating on villi that were not seen in crypt cells. The amplification of the apical microvillus surface between mid and tip levels in well-nourished rats (679-1085 micron2/cell) failed to occur in rats with PEM (807-729 micron2/cell). This resulted in an estimated 60% reduction of total jejunal absorptive surface, from 10,070 cm2 in well-nourished rats to 3975 cm2 in rats with PEM. In contrast, the development of the basolateral surface, which requires much less membrane accrual, was unaffected by PEM. Villus mid and tip cells of rats with PEM also had increased cell volume and mitochondrial volumes. Microvillus surface area per cell appears dependent on the number of microvilli per cell, which equals the cell flat surface times the microvillus numerical density (number of microvilli per square micrometer) in well-nourished rats. However, this relationship was not demonstrable in rats with PEM.

Quantitative morphological methods in intestinal research

Measurements of intestinal length suffer from considerable errors, because of variable degrees of contraction in the longitudinal muscles. In vitro organ bath techniques may solve these problems. Villi and microvilli amplify the internal surface area; measurements of the amplification factors should be based on stereological methods. Villus height and crypt length provide information on mucosal net growth; such data might be useful when studying hypertrophic and hypotrophic conditions. More precise knowledge on cell turn-over requires autoradiographic studies of 3H-thymidine incorporation into nuclei cell. Ultimately, stereological analyses of mucosal components and cell structures will supply detailed information needed for cell biological research.

Stereological studies on the rat small intestinal epithelium. III. Effects of short-term alloxan diabetes

Short-term experimental diabetes was used to explore the effect of hyperplastic adaption of the small intestine mucosa on the structure of its absorptive cells. Diabetes was induced in adult female rats by intravenous alloxan administration under kidney protection; similar rats, injected with physiological saline, served as controls. Quantitative light microscopy, performed after 1 month of diabetes, revealed structural changes in the jejunal mucosa consistent with hyperplasia. These changes comprised increased height of the villi (31%) and increased depth of the crypts (34%) in comparison with the control rats. At the electron microscopical level, stereological measurements of the jejunal absorptive cells revealed a decrease in their apical surface area, both for the apical surface density (24%) and for the enlargement factor due to the microvilli (12%). In the duodenal mucosa, this kind of experimental diabetes did not induce any significant light microscopical or electron microscopical changes of the villi, the crypts, or the absorptive cells. It was concluded that the adaptive capacity of the structure of the small intestine mucosa to short term experimental diabetes is more pronounced in the jejunum than in the duodenum, and that the adaptive response also includes alterations in the structure of the absorptive cells.

Geometric model of the rat intestinal mucosa for stereological evaluation of villus amplification factors

This study was prompted by a desire to compare villus amplification factors at various sites along the small intestine of the laboratory rat. The paper describes a precise and efficient stereological method for achieving this objective. The method relies on conventional intersection counts performed exclusively on transverse sections. Analyses are based on six adult rats. Pieces of small bowel fixed by in situ perfusion were taken from proximal, middle and distal regions. Intersection counts on villus and primary mucosal surfaces were performed on transverse and longitudinal sections through the same regions. These counts revealed that intestinal architecture can be reasonably approximated by the simple geometric model of an isotropic villus surface on an anisotropic (cylindrical) primary mucosal surface. As a result, intersection counts may be confined to transverse sections (to reduce sampling variance) and the appropriate ratio estimator multiplied by the numerical coefficient 4/pi (to obtain an estimate of surface amplification due to villi).

Effects of fasting on villi along the small intestine: a stereological approach to the problem of quantifying villus 'shape'

We present stereological methods for establishing the shapes of villi from simple measurements on histological sections. Villi at different intestinal locations are analyzed in control and fasted rats. Villus shape factors are sensitive indicators of the effects of fasting but estimates of villus height alone are not.

Morphometry of the small intestinal enterocytes of the fasted rat and the effects of colchicine

The function of the microtubules that are present in the villus enterocytes of the mammalian small intestine is virtually unknown. In order to advance our knowledge about enterocyte microtubules, a quantitative ultrastructural comparison was carried out on enterocytes from rats injected intraperitoneally with colchicine (0.5 mg/100 g body weight) in saline and from rats injected with saline alone. Our morphometric and stereologic study demonstrates that colchicine treatment results in 1) an absolute decrease in microtubules, 2) a reduction in microvilli, essentially in length, 3) an increased thickness of the terminal web, 4) an increase in total lysosomal volume, apparently by an increased number of smaller lysosomes, and 5) a decrease in the number of Golgi lamellae. These results along with those from other studies suggest to us that enterocyte microtubules are involved in the biogenesis of microvillus plasma membrane. Our morphometric data from the saline-treated rats essentially agree with comparable data from other studies. However, comparison with comparable data from hamster enterocytes demonstrates species differences.