Influence of bile and pancreatic secretions on the size of the intestinal villi in the rat

The effect of altered luminal nutrition on cellular proliferation and plasma concentrations of enteroglucagon and gastrin after small bowel resection in the rat

Luminal nutrition is known to have a trophic effect on small bowel mucosa after intestinal resection. Humoral agents, however, may also contribute to this process. Two of the proposed humoral agents, enteroglucagon and gastrin, were therefore investigated after intestinal resection and transection in the rat, and changes in their concentration in the plasma were related to cellular proliferation. Forty-eight male Wistar rats had either 75 per cent proximal small bowel resection or jejunal transection. The animals were further divided into three groups, each with a different nutritional intake. The first group were allowed food ad libitum. The second group were kept under hypothermic conditions which resulted in hyperphagia, while the last group were nourished intravenously. A further 8 animals had a laparotomy only (sham operation). All animals were killed 12 days after operation, plasma enteroglucagon and gastrin were measured, while determination of the crypt cell production rate (CCPR) was used to denote cellular proliferation. In each group resected rats had significantly higher crypt cell production rates and greater enteroglucagon levels compared with transected animals. However, only in the normally fed group was plasma gastrin increased in resected animals, there being no significant difference in the plasma concentration of this peptide in transected compared with resected rats, in both the intravenously fed and hyperphagic groups. In the models studied enteroglucagon appears to be a more likely candidate for a humoral trophic agent than gastrin in intestinal adaptation.

Effects of octapeptide-cholecystokinin, secretin, and glucagon on intestinal mucosal growth in parenterally nourished rats

Nutrients in the lumen of the small intestine may cause the release of enteric hormones which directly or indirectly stimulate intestinal mucosal growth. Male Sprague-Dawley rats with either an intact small bowel or following jejunal resection were maintained on total parenteral nutrition (TPN). C-terminal octapeptide-cholecystokinin alone or combined with secretin, or glucagon alone were added to the intravenous nutrient solution and continuously infused. Control rats received only TPN or gastric infusion of isocaloric amounts of TPN solution. After 7 days, intestinal hypoplasia was noted in rats with an intact bowel maintained on TPN alone compared with the gastrically infused group. TPN did not maintain the proximal-distal gradient of mucosal mass. Continuous intravenous infusion of octapeptide-cholecystokinin alone and together with secretin in rats maintained on TPN significantly stimulated small bowel mucosal growth, partially restoring the proximal-distal gradient. Glucagon infusion did not stimulate mucosal growth. Rats with a jejunal resection and maintained on TPN for 7 or 14 days failed to develop mucosal hyperplasia of the ileum in contrast to rats given the TPN solution intragastrically. Continuous intravenous infusion of octapeptide-cholecystokinin in rats maintained on TPN after jejunal resection caused significant mucosal growth in the ileum compared with the rats maintained on TPN alone, but not to the extent seen in gastrically fed animals. Intravenous infusion of octapeptide-cholecystokinin stimulates small-bowel mucosal growth. Secretin appears to have an additional effect when given together with octapeptide-CCK. Although a direct trophic action by these hormones on the intestinal mucosa is possible, this effect is more likely mediated via stimulation of pancreaticobiliary secretions.

Hyperplasia of the exocrine pancreas after small bowel resection in the rat

The effect of a 90% small bowel resection on the exocrine pancreas was investigated over a three month period in adult Wistar rats. Control animals underwent a sham-resection consisting of a transection and reanastomosis of the small intestine. After jejunoileal resection, the wet weight of a gland increased significantly (52%) from the 15th day. The parallel increase in total protein, DNA and RNA content without any modification in the ratios of pancreatic weight, protein, and RNA to DNA suggests that there is cellular hyperplasia but not hypertrophy. Small intestinal resection decreased significantly the amount of amylase when expressed per unit pancreatic weight; it reduced slightly but not significantly that of chymotrypsin, while it did not modify the amount of lipase. However, the total amount of these enzymes in the pancreas remained unaltered when compared with controls. It is concluded that a massive resection of the small bowel induces cellular hyperplasia in the rat exocrine pancreas; this could compensate that reduced level of enzymes in acinar cells.

Ultrastructural changes in the rat exocrine pancreas after jejunoileal bypass

The influence of a 90% jejunoileal bypass on the rat exocrine pancreas was studied by morphometrical procedures. In sham-operated animals exocrine acinar cells accounted for 80.3% of the pancreas volume. These cells are composed of 9.9% nuclei, 8.4% mitochondria, 12.2% zymogen granules, 0.3% lipid droplets and 69.2% of a compartment ("ERGLS") composed of endoplasmic reticulum, ribosomes, Golgi areas, lysosomes and the cytoplasmic ground substance. Intestinal bypass did not change the volume density of exocrine cells nor that of nuclei in the cells during the three postoperative months. The means nuclear diameter was approximately the same in both groups. However, the volume density of secretory granules diminished by 50%. This was accompanied by a decrease in mean granular diameter, but not in their numerical density. The volume density of lipid droplets increased 10 fold, that of mitochondria increased slightly from the 15th postoperative day but significantly from the 45th day. The remaining cellular compartment composed of "ERGLS" was not modified by intestinal bypass. These findings suggest that a 90% jejunoileal bypass induces major changes in the composition of pancreatic acinar cells but not in their size.

Effect of perfusion of a jejunal blind loop on intestinal thymidine uptake in the rat

The effect of perfusing a jejunal loop with saline or glucose solution on the thymidine uptake by the intestinal cells was studied in rats. Two weeks after the construction of the loop, it was perfused for 24 h with glucose or saline of either 280 or 450 mOsm/kg. A control group received no perfusion. The weight per unit length, the DNA concentration, and the DNA-specific activity of 3H-labeled thymidine was recorded in the duodenum, the loop, the remaining small intestine and the colon. The thymidine uptake in the perfused loop relative to the unperfused parts of the small intestine was higher in the groups that received glucose or hypertonic saline than in the groups that received isotonic saline and the control group. In the colon, the uptake relative to the uptake in the unperfused small-intestinal segments was reduced in all the perfused groups compared with the controls. The tissue DNA concentration and the weight per unit length of the intestinal segments were not changed by the perfusions. The results are discussed in relation to current hypotheses on the regulation of intestinal cell proliferation.

Differences in the development of jejunum and ileum as observed in fetal rat isografts. Possible implications related to the villus size gradient

Previous studies have shown that villus size in the small intestine decreases from the duodenum toward the ileum. Villus-enlarging and villus-reducing factors have been found in the gastric, pancreatic, and duodenal secretions, and in bile (Altmann and Leblond, '70; Altmann, '74). We here explore the role of intrinsic factors present in the individual sections of the small intestine by following the development of villus height in fetal (21-day old) jejunal and ileal segments implanted under the kidney capsule of syngeneic adult rats. Twenty-eight and 45 days after implantation, the jejunal villi contained significantly more columnar epithelial cells than did the ileal villi, but the jejunoileal gradient was even greater in small intestine of corresponding ages, developing in situ. Our experiments, thus, show that the jejunoileal gradient is already programmed in rats 1 day before birth, while other factors contribute postnatally to regulation of its magnitude.

Small intestinal and colonic changes induced by a chemically defined diet

Three groups of rats were fed, respectively, a chemically defined diet intragastrically (IG), an equivalent diet intravenously (IV) and solid food orally (CH) for 8 days, and their small intestines and colons compared. All received equal calories. The small intestine was divided into equal proximal (A), middle (B), and distal (C) segments for measurements. Mucosal weight per cm in segments A and B of IG were, respectively, 65 and 38% higher than in IV (P less than 0.01), but 27 and 33% lower than in CH (P less than 0.01). However, in the distal segment, C, mucosal weight in IG was similar to IV and CH was 79% higher (P less than 0.01). DNA and protein followed the same pattern. Segment A sucrase activities were similar in CH and IG and were much higher than in IV (P less than 0.01). Sucrase in IG dropped very rapidly distally so that it became much lower than in CH (P less than 0.05) and similar to IV. Mucosal weight, DNA, and protein in the colon were not significantly different in IG and IV, which were both significantly lower than in CH (P less than 0.01). The results indicate that a chemically defined diet maintains intestinal mass well in the proximal small intestine, but the effect diminishes rapidly in a distal direction so that distal small intestine and colon become atrophied and similar to those in intravenous feeding.

Organ culture of adult mouse intestine. II. Mitotic activity, DNA synthesis and cellular migration after 24 and 48 hours of culture

DNA synthesis, mitotic activity and cell migration have been measured in organ culture of adult mouse jejunum during the first 48 hr. Explants cultured in DMEM-HEPES-NCTC-135 medium present a sharp decrease of mitotic activity in the first hours of culture, but mitoses are restored to 80% of the controls between 24 and 48 hr. DNA synthesis follows the same pattern. Cell migration continues during culture.

Organ culture of adult mouse intestine. I. Morphological results after 24 and 48 hours of culture

Explants of adult mouse intestine have been maintained in organ culture for 24 to 48 hr. The best results have been obtained with a mixture of DMEM-HEPES medium and NCTC-135 enriched with 10% fetal bovine serum. The morphology of the mucosa is well preserved at the light and electron microscopic level: absorbing cells exhibit an increase in secondary lysosomes; goblet cells and Paneth cells remain active; numerous mitoses are observed in the crypts; and vigorous re-epithelization takes place on the margin of the explants.

Pituitary hormones and the small bowel: effect of hypophysectomy on intestinal adaptation to small bowel resection in the rat

The influence of pituitary hormones on intestinal adaptation to small bowel resection was studied by examining jejunal and ileal structure and function in control and in sham-operated rats, and in animals with 50% proximal or distal resection which were divided into three main groups: normally-fed, hypophysectomized. and pair-fed. The pituitary was removed 2 weeks before intestinal surgery and gut structure and function were studied 4 weeks later. The effectiveness of hypophysectomy was confirmed by histological examination of the aspirated pituitary, and by showing a significant subsequent reduction in weight of the testes and adrenals. Food intake and body weight fell significantly after removing the pituitary; intestinal surgery caused a transient further decrease in food intake. Measurements of intestinal villus height and crypt depth, indices of mucosal mass (mucosal wet weight, protein and DNA content/cm intestine), measurements of mucosal alpha-glucosidase activity, and in vivo galactose absorption/unit length of intestine all showed comparable results. In rats with an intact intestine, resection resulted in mucosal hyperplasia and increased segmental absorption. Following hypophysectomy, there was marked mucosal hypoplasia and hypofunction which seemed to be due largely to associated hypophagia since comparable changes were found in the pair-fed, sham-operated rats. However following pituitary removal, both distal jejunum and proximal ileum retained their capacity to regenerate though the magnitude of this adaptive change was much greater in the resected, pair-fed rats suggesting that hypophagia alone cannot explain the diminished adaptation to resection after hypophysectomy. By inference, pituitary hormones do influence the adaptive response to resection.

Epithelial cell population kinetics of isolated ileal loops (thirty-vella fistulae) after 40% small in testinal resection. Autoradiographic studies in the rat

The influence of 40% small intestinal resection on epithelial cell population kinetics of isolated ileal loops (Thirty-Vella fistulae) was investigated by autoradiography with H3-thymidine in the rat. Sixty days after resection increases were found in the size of the proliferative (0.05 less than P less than 0.1) and villous (P less than 0.01) zones. In isolated ileal loops of animals not subjected to 40% small bowel resection proliferative and villous zones were reduced in size in comparison to those of ileum in continuity in a group subjected to jejunal transection and anastomosis (P less than 0.002). The findings support the hypothesis that villous size is increased after resection by the action of a systemic factor. However, they provide only limited evidence for the influence of a systemic factor on crypt cell proliferation.

The relationship between the functional and structural alterations in the rat small intestine following proximal resection of varying extents

The functional and structural characteristics of the ileal remnant of rat intestine were examined four weeks after 45%, 70% or 95% proximal resection. The increase in villus height in the ileal remnant had alfread reached its maximum after a resection of 45%, whereas a further increment in the length of the crypts occurred after 70% resection. There was an increase in the number of enterocytes per unit length of villus and a rise in the DNA content per unit weight of mucosal scrapings, which testifies to the development of mucosal hyperplasia in this situation. The specific activities of sucrase, measured biochemically, and of nonspecific esterase, determined histochemically, were reduced in proportion to the extent of the resection. Similarly, the uptakes of L-phenylalanine and of beta-methyl-D-glucoside by intestinal rings in vitro were progressively diminished in the ileal remnant. There was an increase in the rate of disappearance of glucose from a perfused loop in vivo, when expressed in terms of unit intestinal length. Galactose absorption remained unchanged, but when expressed in terms of unit dry tissue, was significantly reduced, in agreement with the diminished transport of both amino-acids and monosaccharides in vitro.

Alcohol ingestion-induced changes in the human rectal mucosa: light and electron microscopic studies

Histologic and ultrastructural examination of specimens of rectal mucosa from 11 patients who had recently consumed excessive quantities of alcohol revealed marked pathologic changes. Goblet cells were decreased and a dense mononuclear cell infiltrate was seen on light microscopic study. Electron microscopy revealed swollen, distorted mitochondria and dilated and vesicular endoplasmic reticulum. These abnormalities disappeared after two weeks' abstinence. It is suggested that disordered organelle structure and function might contribute to the diarrhea frequently observed following excessive alcohol intake.

Enterocyte turnover and content in fat-fed hamsters

Cryptal lecithin-synthesizing enzyme specific activities have been previously demonstrated to be increased by feeding a fat-supplemented diet to hamsters. To determine if a physiological basis exists for such changes [3H]thymidine incorporation, cellular migration rate, and mucosal concentration of DNA, protein, and lecithin were measured. Radioautographic studies showed that the labeling index and cell migration rate throughout the intestine in the fat-fed hamsters and in the proximal three-quarters of the intestine of the control group were the same. Both parameters were reduced in the distal quarter of the control intestine. The protein/DNA ratio was significantly increased in the proximal three-quarters and modestly in the distal quarter of the intestine of the fat-fed group as compared to controls, suggesting cellular hypertrophy. The lecithin content of the proximal three-quarters of intestine was the same in both groups but reduced in the distal quarter of the gut of the fat-fed group. These studies suggest that lipid feeding in the hamster can have profound effects on intestinal cellular content and turnover.

Ileal epithelial cell migration after 40% small-bowel resection. Autoradiographic studies in the rat

Adaptation in the small bowel after resection is associated with increases in crypt cell proliferation and villus height. This paper gives the results of an autoradiographic investigation with [3H]thymidine of epithelial cell migration 60 days after 40% small-bowel resection in the rat. The mean number of cell positions between the crypt--villus junction and the leading labeled cell 30 hr after injection was increased by 19.4% in the resected group (P less than 0.02). The mean total number of cells per villus column was increased by 27.8% (P less than 0.002). Migration rate estimated in cell positions per hour was accelerated by 18.9% (P less than 0.001) after resection. The 8.1% lengthened life span of villus cells was not statistically significant. The increased number of cells per villus column and unaltered life span of villus cells would facilitate functional adaptation. The causal relationship between the larger villus cell population and accelerated migration after resection and increased crypt cell proliferation is unknown.

The effect of transposition to jejunum on epithelial cell kinetics in an ileal segment

Epithelial cell kinetics were studied in an ileal segment after transposition to proximal jejunum. The number of cells per villus column in the transposed ileum increased after 4--7 days to reach values normal for jejunum after 14--30 days. This increase was accompanied by a simultaneous increase in the number of cells per crypt column up to 130% of values in jejunum and ileum in situ. The percentage of labelled crypt cells, after labelling with 3H-thymidine, and the relative size of the proliferative cell compartment in the crypt in the transposed ileum did not differ from values in the ileum in situ at any time interval after surgery. The total proliferative activity per crypt, which was determined by scintillation counting of isolated crypts after 3H-thymidine labelling, increased two-fold from 7 days after surgery. Cell migration studies showed that the increase in the number of villus cells was probably not caused by a change in the life span of the epithelial cells. It seems that the increase in the number of villus cells in ileal epithelium after transposition to proximal jejunum is brought about by an enlargement of the crypt, while the relative size of the proliferative cell compartment in the crypt remains unchanged.

An experimental model for studies on the effects of food and digestive secretions on the digestive-absorptive capacity of rat small intestine

At an average of 32 days after a modified Roux-en-y repositioning of rat small intestine, the mucosal mass, mucosal composition, in vivo absorption of galactose and the activity of maltase, sucrase and alkaline phosphatase were measured. In the gut segment with digestive secretions but without food (A) the only change was a decrease of sucrase activity which occurred most probably at the cellular level. In the gut segment with food and gastric juice and a reflux of digestive secretions (B) complex changes took place. An increase in mucosal mass was not accompanied by an increase in galactose absorption. There was a high increase of sucrase activity, a moderate increase of maltase activity and a tendency of the alkaline phosphatase activity to decrease. The changes (increase in mucosal mass and total enzyme activity, but no changes in activity at the cellular level) in the segment exposed to both digestive secretions and food (C) were compatible with a more proximal promotion of a distal gut segment.

Gastrointestinal adaptation following small bowel bypass for obesity

Small intestinal morphologic and biochemical changes were studied following jejuno-ileal bypass for obesity after body weight stabilization had occurred. Four patients underwent biopsy of in-continuity and bypassed jejunal and ileal segments of the small intestine 11 to 22 months after the bypass operation. Microscopically, marked mucosal villus hypertrophy of the in-continuity bowel was observed, especially in the ileum. Bypassed jejunal mucosa underwent atrophy compared with pre-bypass jejunum, whereas bypassed ileum appeared similar microscopically to pre-bypass ileum. The specific activities of mucosal disaccharidase enzymes (maltase, sucrase, lactase and trehalase) in units per mg protein remained similar to pre-bypass levels in segments of the in-continuity jejunum and the bypassed jejunum and ileum. On the other hand, elevated mucosal disaccharidase levels were measured in biopsy specimens of the in-continuity ileum. Total enzyme activity per unit length of intestine, however, was estimated to be elevated in both in-continuity jejunum and ileum secondary to mucosal villus hypertrophy. These data indicate that following small bowel bypass: (1) the in-continuity ileum undergoes greater biochemical and morphologic adaptation than the jejunum; and (2) intraluminal nutrients and chyme appear to be essential to maximal intestinal adaptation.

Colonic epithelial cell proliferation after 40 percent intestinal resection. Autoradiographic studies in the rat

Colonic crypt cell population kinetics were investigated by autoradiography with tritiated thymidine in rats 60 days after resection of a jejunal segment equivalent to 40% of the length of the small intestine. Controls were subjected to transection and anastomosis. The mean total number of cells and the mean number of labelled cells per crypt cell column were estimated. The distribution of the proliferative and mature cell zones was obtained by determing the percentage of labelled cells at each cell position in the crypt cell columns. The mean total number of cells, mean number of labelled cells per crypt cell column and sizes of the proliferative and mature cell zones were unchanged (P less than 0.1). It is concluded that 40% small intestine resection does not influence the cell population kinetics of the colonic crypts of Lieberkühn.

Relationship between the changes in gastrin levels and intestinal properties in the starved rat

Intestinal DNA, RNA, and protein content were decreased to a greater extent than was body weight when rats were starved for 3 days. Specific lactase and maltase activity increased with progressively longer periods of starvation. Antral and serum gastrin concentration significantly decreased during the 3 days of starvation. Pentagastrin (250 mug/kg 3 times daily) was injected into a group of rats for the duration of a 3-day starvation period and caused a small but significant increase in the relative intestinal RNA and protein content and decreased lactase and maltase specific activities in comparison with the levels of 3-day starved controls. Pentagastrin thus partially reversed some of the starvation-induced changes toward fed levels. Thus, a deficiency in the trophic hormone gastrin may be partially responsible for the disproportionate changes in intestinal tissue during starvation.

A region of mitochondrial division in the epithelium of the small intestine of the rat

Electron microscopic examination of samples from various regions of the rat small intestine was carried out. The number of mitochondria in the epithelial cells was estimated. The counts were made in sections of cells cut along their longitudinal central plane. The errors involved in extrapolating these counts to the whole cells were also estimated. The average mitochondrial number per cell section was 21 in the lower third of the crypts, it gradually increased in the mid and upper thirds and reached about double, 42, at the villus base. The known forms of dividing mitochondria were identified in the mid and upper third of the crypts. The counts remained around 42 along the epithelium of the villi. Crypt cells are continually produced in the lower crypt; these cells migrate to the villi while differentiating into nonproliferative absorptive cells. After inhibiting mitosis by methotrexate, this migration continued (Altmann, '74) and mitochondrial division persisted. In segments of the jejunum isolated surgically from the functional intestine for three weeks, mitosis and cell migration continued, but no evidence of mitochondrial duplication was found. Each mitochondrion probably undergoes a division as the crypt cells migrate from the mid-crypts to the villus. As a result, the villus epithelial cells contain double numbers of mitochondria. It appears that the mitochondrial division is not directly related to mitosis and is elicited by a stimulus present only in the functional intestine.

Morphological effects of a large single dose of cycloheximide on the intestinal epithelium of the rat

Adult male rats received 15 mg/kg cycloheximide and the subsequent morphological effects at three and six hours after injection were evaluated using histometry, light and electron microscopy, histological demonstration of terminal web and acid phosphatase, and radioautography with tritiated thymidine. Rapid atrophy of the villi took place, progressing from the villus tip by premature exfoliation of epithelial cells. The crypts also diminished by random exfoliation of many crypt cells and by partial or complete disintegration. Mitosis and epithelial cell migration were absent. By six hours, the area occupied by the villi and the crypts per unit length of histological section was decreased by about 70-90% in most of the small intestine but only by about 40-60% in the duodenum and the terminal ileum. In the upper half of the villi, the epithelium was strongly positive for acid phosphatase and contained large numbers of round bodies resembling primary lysosomes. In the lower half, the microvillous border and terminal web were found to be disrupted. Animals receiving only 5 mg/kg cycloheximide also showed the atrophy of villi and crypts, and the round bodies resembling lysosomes. Evidence from several sources has indicated that protein synthesis in normal villus epithelial cells subsides toward the villus tip and becomes minimal at exfoliation. At exfoliation, proteins responsible for epithelial cohesion probably fail because they are no longer replenished. Cycloheximide appears to accelerate this process.

Organ culture of adult guinea-pig intestine. III. Mitotic-activity and cellular migration

The mitotic activity and the cellular migration have been studied in explants of adult guinea pig intestine cultured for 24 hours. The mitotic index after a significant increase in the first hours of culture, decreases steadily thereafter. The DNA synthesis persists in the crypts for 24 hours at least and cell migration can be observed. These results demonstrate that organ culture of adult intestine may be used as a model for the study of intestinal function.

Changes in sucrase, enterokinase, and peptide hydrolase after intestinal resection. The association of cellular hyperplasia and adaptation

In a study of changes in digestive enzymes after massive intestinal resection and the mechanisms by which such changes occur, rats were sacrified 4 wk after removal of the proximal two-thirds of the small intestine. Alterations in the mucosal levels of sucrase, enterokinase, and dipeptide hydrolase (L-leucyl-L-alanine substrate) were examined in the light of associated changes in protein. DNA and wet mucosal weight, measured in standardized gut segments from various regions of intestine. Metabolic studies showed that normal growth patterns were reestablished after the operation but significant elevations in stool weight and fecal nitrogen occurred in the second postoperative week, falling towards normal by the 4th wk. In standard gut segments wet weight of mucosa, protein, and DNA rose, especially in distal segments, DNA increasing disproportionately. Mucosal levels of the proximally distributed and membrane-bound enzymes, sucrase and enterokinase, showed similar patterns of change: when enzyme activity was expressed in terms of the total per segment, proximally there were considerable increases in both enzymes, but, expressed in terms of specific activity, that of sucrase fell and that of enterokinase was unaltered. By contrast, the largely soluble and more distally distributed dipeptide hydrolase increased more in distal segments and the increases in total activity were accompanied by lesser increases in specific activity. However, in spite of increases in total activity, enzyme activity per milligram DNA fell by over 50% in postanastomotic segments. Subcellular distribution studies showed no change in the percentage of the total activity which was membrane-bound and zymograms confirmed that no new dipeptide hydrolase had appeared after resection. It is concluded that increases in the segmental totals of various enzymes seen after resection are achieved by disproportinate increases in the number of mucosal cells per segment and that the greatest change in a particular enzyme occurs in the region where the enzyme is normally found in highest concentration.