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

[Short bowel syndrome in children: a diagnosis and management update]

Short bowel syndrome (SBS) refers to the sum of the functional alterations that are the result of a critical reduction in the length of the intestine, which in the absence of adequate treatment, presents as chronic diarrhea, chronic dehydration, malnutrition, weight loss, nutriment and electrolyte deficiency, along with a failure to grow that is present with greater frequency during the neonatal period. The aim was to carry out a review of the literature encompassing the definition and the most frequent causes of SBS, together with an understanding of its physiopathology, prognostic factors, and treatment. An Internet search of PubMed articles was carried out for the existing information published over the last 20 years on SBS in children, using the keywords "short bowel syndrome". From a total of 784 potential articles, 82 articles were chosen for the literature review. The treatment of patients presenting with SBS is quite a challenge and therefore it is necessary to establish multidisciplinary management with a focus on maintaining optimal nutritional support that covers the necessities of growth and development and at the same time provides a maximum reduction of short, medium, and long-term complications. The diagnosis and treatment of a child with SBS require a team of professionals that are experts in gastroenterologic, pediatric, and nutritional management. The outcome for the child will be directly related to opportune management, as well as to the length of the intestinal resection and the presence or absence of the ileocecal valve.

Region-specific adaptation of apical Na/H exchangers after extensive proximal small bowel resection

After massive small bowel resection (MSBR), the remnant small intestine adapts to restore Na absorptive function. The possibility that this occurs through increases in cellular Na absorptive capacity was examined by assessing the regional effects of 50% proximal MSBR on the function and expression of the apical membrane Na/H exchangers (NHEs) NHE2 and NHE3. Morphometric analysis confirmed adaptive changes consistent with villus hypertrophy, particularly distal to the anastomosis. Villus epithelium prepared by light mucosal scrapings from 2-wk-postresected and -posttransected control rats exhibited comparable brush-border hydrolase activities, total cell protein per DNA, and villin expression but increased basolateral Na-K-ATPase activity. Parallel increases of two- to threefold in protein and mRNA abundance of NHE2 and NHE3 were observed only in ileal regions distal to the anastomosis of resected rats. Basolateral NHE1 expression was unchanged. After 80% resection, increases in NHE2 and NHE3 became evident in proximal colon. We conclude that increased enterocyte expression and function of apical membrane NHEs in regions distal to the anastomosis play a role in the adaptive process after MSBR. The increased luminal Na load to distal bowel regions after proximal resection may stimulate increases in apical membrane NHE gene transcription and protein expression.

Anomalous apical plasma membrane phenotype in CK8-deficient mice indicates a novel role for intermediate filaments in the polarization of simple epithelia

Previous results from our laboratory have indicated a requirement for CK intermediate filaments (IF) for the organization of the apical domain in polarized epithelial cells in culture. The results seemed to be challenged by the phenotype of cytokeratin (CK) 8-deficient mice, which comprises only colorectal hyperplasia, female sterility and a weaker hepatocyte integrity. In this work localization with anti-CK antibodies indicated that many Ck8-/- epithelia still form IF in CK8-deficient mice, perhaps because of the expression of the promiscuous CK7. In the small intestine, only villus enterocytes lacked IFs. These cells appeared to lose syntaxin 3, and three apical membrane proteins (alkaline phosphatase, sucrase isomaltase and cystic fibrosis transmembrane conductance regulator) as they progressed along the villus. At the distal third of the villi, gamma-tubulin was found scattered within the cytoplasm of enterocytes, in contrast to its normal sub-apical localization, and the microtubules were disorganized. These results could not be attributed to increased numbers of apoptotic or necrotic cells. The only other cell type we found without IFs in CK8 null mice, the hepatocyte, displayed increased basolateral levels of one apical marker (HA4), indicating a correlation between the lack of intermediate filaments and an apical domain phenotype. These data suggest a novel function for intermediate filaments organizing the apical pole of simple polarized epithelial cells.

Keratinocyte growth factor enhances early gut adaptation in a rat model of short bowel syndrome

OBJECTIVE

To evaluate the effects of keratinocyte growth factor (KGF) on intestinal adaptation after resection of 85% of the small intestine and consider its potential application in short bowel syndrome (SBS).

STUDY DESIGN

Experimental study using a known model of SBS.

ANIMAL POPULATION

Thirty male Sprague Dawley rats.

METHODS

Four groups of animals were designated. Two groups underwent 85% resection of the small intestine, while the other two groups were sham-operated, undergoing transection and reanastomosis. Resected and sham-operated groups then received either 3 mg/kg KGF or vehicle subcutaneously daily for 3 days. Gut adaptation was evaluated by measurements of mucosal cellularity and biochemical activity in duodenal, jejunal, and ileal segments.

RESULTS

Significant small intestinal growth after bowel resection alone was confirmed in resected versus sham-operated rats. KGF further augmented this growth in the resected animals. Mucosal wet weight of the small intestine increased with resection and was further increased (by 20% or more) with KGF administration. Mucosal thickness, villus length, and crypt depth exhibited similar patterns of response. The KGF-induced increase in mucosal morphology was accompanied by increased mucosal DNA and protein content, followed by a trend toward increased mucosal enzyme activity. Histology demonstrated an increase in goblet cells in KGF-treated animals. In situ hybridization analysis demonstrated that KGF markedly increased mucosal expression of intestinal trefoil protein (ITF) mRNA.

CONCLUSIONS

KGF enhances gut growth, differentiation, and gene regulation during adaptation in rat small intestine after massive resection.

CLINICAL RELEVANCE

KGF may be beneficial in the management of veterinary and human patients undergoing massive intestinal resection.

Magnitude of functional adaptation after intestinal resection

Intestinal adaptation after resection has been much studied, but rarely examined in an integrative context. Hence we assessed the effects of resection and subsequent adaptation on the quantitative relationship between dietary glucose load and gut capacity to transport glucose. The ratio of capacity to load is termed the "safety factor." Our objectives were to determine 1) the time course of intestinal adaptation after resection, 2) whether adaptation is quantitatively complete, 3) whether survival requires maintaining a safety factor of at least 1.0 for glucose transport, 4) the effect of altered energy demands on adaptation, and 5) the relationship between the amount of tissue removed and the magnitude of functional adaptation. We performed 80% resection of the small intestine on Sprague-Dawley rats and measured small intestinal glucose uptake capacity, dietary glucose load, and gut gross morphology at 1, 5, and 10 wk postsurgery. Nearly all aspects of adaptation were complete by 1 wk postsurgery. After resection, remnant small intestine mass increased by over fivefold within 1 wk, to reach 50-70% of its preresection value. However, mass-specific glucose uptake activity was reduced, so that intestinal regeneration restored uptake capacity to only 33% of control values. Increased energetic demands had only modest effects on intestinal adaptation. Although the safety factor for small intestinal glucose uptake remained <1.0 (i.e., capacity < load) after adaptation to resection, nearly all rats survived. Hindgut fermentation of nonabsorbed nutrients appeared to contribute to that survival, despite inadequate small intestinal capacity. After less massive resection surgeries (25, 50, and 75% resections), the percent increase in glucose uptake capacity increased with the amount of tissue removed.

Short-chain fatty acids increase proglucagon and ornithine decarboxylase messenger RNAs after intestinal resection in rats

BACKGROUND

Intestinal adaptation is a complex physiological process that is not completely understood. Systemic administration of short-chain fatty acids (SCFAs) has been shown to facilitate adaptation to small bowel resection; however the mechanisms underlying this phenomena are unknown.

METHODS

Forty-six male Sprague-Dawley rats underwent an 80% jejunoileal resection and jugular catheterization. After surgery, rats were randomly assigned to receive standard total parenteral nutrition (TPN) or an isoenergetic, isonitrogenous TPN supplemented with SCFAs. On day 3 or 7 after surgery, ileal samples were removed for determination of mucosal wet weight, DNA, RNA, and protein concentrations. Total cellular RNA was extracted for use in Northern blot analysis to quantify proglucagon and ornithine decarboxylase messenger RNAs (mRNAs).

RESULTS

Total, mucosal, and submucosal weights were increased (p < .05) in the SCFA group both 3 and 7 days after surgery. Ileal DNA and RNA concentrations were increased (p < .05) in the SCFA group at both time points; however ileal protein concentration did not differ between groups until 7 days after resection. Levels of proglucagon and ornithine decarboxylase messenger RNAs were higher (p < .05) in the SCFA group at both time points.

CONCLUSION

The upregulation of proglucagon and ornithine decarboxylase gene expression may be the mechanism by which SCFAs facilitate intestinal adaptation.

Adaptation of rabbit small intestinal brush-border membrane enzymes after extensive bowel resection

Short lengths of small intestine may be resected without significantly affecting the digestive and absorptive capacity; however, extensive resection produces varying degrees of malnutrition. This study was undertaken to define the adaptive changes in the remaining small intestine of two of the jejunal and ileal mucosal brush-border membrane enzymes after extensive small bowel resection in rabbits. Thirty adult New Zealand White rabbits underwent a 50% to 60% jejuno-ileal-enterectomy with end-to-end anastomosis. Maltase activity (UE/g protein) increased from 152 (preoperative) to 392 at 3 weeks in the proximal segment and from 85 to 259 in the distal segment; these levels decreased to 222 and 155 in the respective segments at 6 weeks. AOP activity (UE/g protein) increased from 154 (preoperative) to 171 in the proximal segment and 171 to 256 in the distal segment at 3 weeks, and was 131 and 288 in the respective segments at 6 weeks. This marked increase in the mucosal brush-border enzymatic activities at 3 weeks postoperatively was associated with a 28% increase in bowel length. By 6 weeks the enzyme levels had decreased slightly; however, there was a persistent 41% increase in bowel length over that immediately postoperation. The mucosal surface area increased from 295 mm2 immediately postoperation to 5,337 mm2 at 3 weeks and 7,635 mm2 at 6 weeks, a 250% increase. The authors conclude that there is an immediate compensatory increase in villus length as well as brush-border enzymatic expression in the remaining intestine that gradually declines as the small intestinal surface area continues to increase and the bowel lengthens with time.

Colonic fermentation and nutritional recovery in rats with massive small bowel resection

BACKGROUND/AIMS

After massive small bowel resection, malabsorbed carbohydrates reach the colon and undergo fermentation. This study investigates the role of colonic fermentation in rats with 80% small bowel resection on weight gain, nitrogen balance, body composition, and intestinal adaptation.

METHODS

Resected or transected rats were fed a liquid diet enterally for 16 days with or without 30 mg/kg metronidazole to reduce fermentation. Weight gain was monitored until the rats were killed. Carcass composition, short-chain fatty acids in cecal content, total nitrogen output, and intestinal mucosal dry weight, protein, and DNA were measured.

RESULTS

Resected rats without metronidazole had a significantly better weight gain, carcass protein, nitrogen balance, and mucosal dry weight, protein, and DNA compared with that of resected rats receiving metronidazole. There were no significant differences between the two transected groups.

CONCLUSIONS

Decreasing colonic fermentation, measured by short-chain fatty acids in cecal content, reduced intestinal adaptation and nutritional recovery in rats with massive small bowel resection.

The value of in vivo electrophysiological measurements for monitoring functional adaptation after massive small bowel resection in the rat

The process of functional adaptation after extensive small bowel resection is complex and imprecisely understood. In vivo electrophysiological measurements for monitoring the functional adaptive process after massive small bowel resection in Brown-Norway rats were evaluated. Rats underwent either a sham operation (SH) or a 90% small bowel resection (SB). Standard rat chow was fed in unlimited quantities. At three or 10 weeks after operation, jejunal and ileal transepithelial potential differences (PD, mV) were determined. Electrogenic ion transport in the villus was measured after glucose (sodium coupled active glucose absorption; PD-glu) and in the crypt, after theophylline infusion (theophylline stimulated chloride secretion; PD-theo). Biopsies were taken simultaneously. Each experimental group consisted of three to five animals. At three weeks the PD-theo and PD-glu in SB rats were significantly lower than in SH rats in both jejunal and ileal segments. At 10 weeks PD-theo and PD-glu were significantly diminished in the jejunal segment of the SB rats compared with the SH rats. The values of PD-theo and PD-glu in the ileal segments were, however, no longer different between the two groups. Three and 10 weeks after operation the length of the villi in the SB group was increased significantly compared with the SH controls. These results indicate that in the early phase of adaptation in vivo electrophysiological variables do not correlate with histological changes in the SB rats. This might be due to cell immaturity resulting from an increased rate of cell turnover or lack of intercellular tight junctions. This hypothesis is supported by a recovery of PD responses in the ileum 10 weeks after resection.

Differentiation status of rat enterocytes after intestinal adaptation to jejunoileal bypass

The differentiation status of epithelial cells in intestinal adaptation remains unclear. To determine whether enterocytes reach optimum maturity following adaptation after 85% shortening of the rat gut by jejunoileal bypass surgery, activities of two brush border enzymatic markers of differentiation, alkaline phosphatase and sucrase, were examined in subpopulations of epithelial cells isolated sequentially from the villus/crypt axis of normal (sham operated) and hyperplastic mucosa. In jejunal villi, adaptational hyperplasia was associated with an increase in total epithelial alkaline phosphatase, but not total sucrase, activity; alkaline phosphatase activity increased most obviously in cells at the 11-50% position (from the tip) on villi. In hyperplastic ileal villi, total alkaline phosphatase activity fell, although sucrase activity did not change significantly. Specific activity (per mg protein) of sucrase on jejunal villus epithelium was reduced by the adaptational changes to bypass; alkaline phosphatase specific activity remained unchanged. In the ileum, despite adaptational changes to bypass, there was no increase in the normally low specific activities of sucrase and alkaline phosphatase. Bypass surgery did not change the major site of expression of either enzyme on jejunal or ileal villi. In conclusion, enzymatic markers of functional differentiation are not all equally affected by adaptational hyperplasia. Hypertrophy of villi and increased cell proliferation seen in jejunum remaining exposed to luminal contents resulted in an increase in the alkaline phosphatase but not the sucrase content. This is not, therefore, the result of a simple immaturity of villus cells. Morphological adaptation in the ileum, however, is not accompanied by adaptation of brush border enzyme markers of differentiation, confirming a functional immaturity of these cells. Strategies for increasing the expression of these markers may have clinical value.

Comparative effect of distal and proximal intestinal resection and bypass on the rat exocrine pancreas

We studied the effects of small-bowel resection and bypass on pancreatic function in rats subjected to a 50% distal resection (DR), a 50% proximal resection (PR), a 50% jejunal bypass (BP) or an intestinal transection (SH) (controls). Duodenal contents were collected after cannulation (under basal conditions). Afterwards, an in vivo duodenal perfusion was made using a glucose/saline solution and perfusate was collected for 1 h. Following this, a cholecystokinin (CCK) solution was injected into the jugular vein (1 U/kg body wt.) and perfusion continued for another 1 h. Basal duodenal volume only increased in rats with a PR, and no significant changes occurred in protein content. In basal conditions, no decreases in amylase, lipase, trypsin, or chymotrypsin activities after DR, PR or BP were detected. When animals were subjected to a perfusion and CCK stimulation, no significant changes occurred in animals with BP; the volume was maintained in rats with PR and DR but a decrease in protein and enzymatic contents was found. We concluded that, in basal conditions, the lack (resections) or exclusion (BP) of 50% of the small bowel does not negatively affect the digestive function. When however, a sustained activity is required, the extirpation of intestinal surface provokes a fall in enzymatic activities and is not modified if only the intestinal transit is suppressed, as occurs in the cases of BP.

Systemic factors are trophic in bypassed rat small intestine in the absence of luminal contents

Mucosal histology, crypt cell proliferation and brush border enzymes were measured in rats with varying degrees of jejunoileal bypass, in order to compare the effect of systemic and luminal factors on adaptive growth and differentiation (brush border enzymes) in small intestinal epithelium. Eighty five percent jejunoileal bypass caused a functional short gut; in intestine remaining in continuity there were significant increases in segmental weight, villus area and crypt depth, compared with sham operated controls and 25% jejunoileal bypass rats. Despite villus cell hyperplasia in 85% bypass rats, mucosal sucrase and alkaline phosphatase fell in jejunum and remained low in ileum, while leucine amino peptidase rose in ileum. There was a significant fall in villus area (p less than 0.01) and crypt cell production (p less than 0.001) in self emptying loops of 25% bypass rats not exposed to luminal contents compared with control segments of sham operated rats. In contrast, self emptying loops of 85% bypass rats were not atrophied despite the much greater distance from luminal nutrients; the villus area (p less than 0.01) and crypt cell production (p less than 0.005) were higher than in 25% bypass rats, and at least as great as in sham operated rats. These results indicate that adaptive hyperplasia has a variable effect on expression of brush border enzymes which might reflect villus cell immaturity. The atrophic effect of diversion of luminal contents can be counteracted by systemic growth factors released as part of the adaptive response; thus systemic growth factors are not dependent on a permissive effect of luminal contents.

Changes in serum and intestinal diamine oxidase (DAO) activity after proximal enterectomy in rats. Correlation of DAO activity with mucosal mass parameters

To determine whether serum and mucosal DAO activity reflects quantitative changes in the small bowel mucosal mass, we have chosen an experimental model of mucosal hyperplasia which is known to occur in the rat after enterectomy. A 50% proximal enterectomy or a single transection was performed in 20 growing rats weighing 145-160 g. Ten days following surgery, we determined mucosal mass parameters (weight, protein, and DNA content), sucrase activity, and DAO activity in the duodenum (segment A), proximal ileum (segment B), and distal ileum (segment C) of the remaining small intestine. Mucosal hyperplasia was demonstrated by the finding that in each segment, mucosal weight, protein, and DNA content per centimeter of gut length were significantly (P less than 0.01) higher (+38 to + 78%) in the resected group than in transected controls. In segments B and C of resected rats, the changes in DAO activity expressed per gram of mucosa paralleled the changes in mucosal mass, the activity being increased by +69% and +49% (P less than 0.05) compared to the values recorded in transected controls. Expressed per centimeter of gut length, total DAO activity was also enhanced by +141% in segment B (P less than 0.05 vs controls) and by +87% in segment C (P less than 0.01 vs controls) of resected rats. In the duodenum, the changes in DAO activity were small (+36%) and not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

D-galactose absorption for the whole intestinal surface after different types of resection and bypass

In vivo D-galactose absorption by the whole intestine between duodenum and rectum was studied in rats 1 month after sham operation, 50% proximal resection, intestinal bypass, or 50% distal resection. The total serosal areas were evaluated by means of an integrative method, obtaining reduced surfaces in resected or bypassed animals as compared with controls. The rate of D-galactose absorption, measured within 10 min, increased after proximal resection and bypass and diminished after distal resection, although the level was similar to that of controls at higher substrate concentrations. When expressed as serosal area, results in proximal and bypassed animals were higher than in controls, without differences (at lower galactose concentrations), and increased (at 25 mM), after distal resection. The total absorptive capacity related to wet and dry weight showed no differences in proximal and bypassed groups and a decrease after distal resection. The above results confirm a good level of recuperation when proximal intestinal surface is excluded. In case of ileal extirpation, a smaller compensatory response was found, which would be compensated for by a high substrate concentration in the intestinal lumen.

Single-villus analysis of disaccharidase expression by different regions of the mouse intestine

1. The present results describe how a new technique of whole-tissue cytochemistry can be combined with automatic scanning of microdissected villi to measure the capacity of individual villi to hydrolyse disaccharides in different parts of the small intestine. 2. Intact villi from the mouse proximal jejunum are found to be eight times more effective than ileal villi in hydrolysing 2-naphthyl-alpha-D-glucoside, an artificial substrate for enzymes normally hydrolysing sucrose, maltose, isomaltose and trehalose in adult intestine. Homogenates of jejunal scrapings are four times more effective than ileal homogenates in hydrolysing this substrate. This discrepancy arises from relating enzyme activities to homogenate protein in cases where intestinal structure changes. 3. The eightfold difference in villus alpha-glucosidase activity is associated with a threefold difference in villus surface area. This discrepancy in turn reflects changes in the capacity of individual enterocytes to express alpha-glucosidase during migration along the crypt-villus axis. These results emphasize the futility of trying to gauge intestinal function from measurement of intestinal structure. 4. Differences between ileal and jejunal villus alpha-glucosidase activities have been further partitioned into those depending on villus structure and those depending on enterocyte development. Present results are discussed in relation to the ability of luminal nutrition to maintain a proximal-distal gradient of digestive enzyme function in the small intestine. The general applicability of this method of analysis to other studies of adaptive response is also emphasized.

Increased activity of digestive enzymes in ileal enterocytes adapting to proximal small bowel resection

The ability of adapting ileal enterocytes to express different digestive enzymes in their brush border membranes was tested in young female Wistar rats (n = 72) receiving 60% proximal small bowel resection. In control rats with intestinal transection both neutral aminopeptidase and alpha-glucosidase activities were shown, by quantitative cytochemistry, to increase during enterocyte migration over the lower part of the villus; thereafter enzyme activities declined or remained approximately constant. Proximal enterectomy increased the amount of alpha-glucosidase but not neutral aminopeptidase activity appearing during early enterocyte development. Thymidine labelled autoradiography showed that the rate of enterocyte migration along the ileal villus nearly doubled after jejunal resection (19.3 v 11.1 microns/h). Nevertheless, the time taken for both peptidase and saccharidase activities to appear at maximal rates in the brush border membrane was diminished by about five hours. Thus ileal enterocytes adapt to proximal small bowel resection by selective increments in enzyme expression, findings that contradict the previous hypothesis of simple metabolic immaturity.

Sodium-dependent D-glucose transport in brush-border membrane vesicles after massive distal small bowel resection in the rat

Massive small intestinal resection in the rat results in both structural and functional changes in the residual small bowel. Sodium-dependent D-glucose transport was examined in brush-border membrane vesicles derived from the proximal small bowel mucosa of male Sprague-Dawley rats 2 and 6 wk after a 66% distal jejunoileal resection or jejunoileal transection. Kinetic characteristics for the low-affinity, high-capacity system and high-affinity, low-capacity system were defined with rapid filtration under conditions of a zero-trans, 100 mM cis-NaSCN gradient. Mucosal weight, protein, and deoxyribonucleic acid content were increased in the residual intestinal segment compared to transected controls and morphometric studies revealed increased villus and crypt heights as well as an increased mitotic index. Postresection mean kinetic parameters for D-glucose transport at 2 wk (low-affinity system: Km, 177.5 +/- 45.1 microM; Vmax, 3.73 +/- 0.99 nmol X mg protein-1 X min-1; and high-affinity system: Km, 6.2 +/- 1.9 microM; Vmax, 0.12 +/- 0.06 nmol X mg protein-1 X min-1) and 6 wk (low-affinity system: Km, 267.8 +/- 83.1 microM; Vmax, 0.06 +/- 0.01 nmol X mg protein-1 X min-1; and high-affinity system: Km, 6.5 +/- 1.1 microM; Vmax, 0.06 +/- 0.01 nmol X mg protein-1 X min-1) were similar to values post-transection at 2 wk (low-affinity system: Km, 280.4 +/- 53.7 microM; Vmax, 3.05 +/- 0.32 nmol X mg protein-1 X min-1; and high-affinity system: Km, 9.1 +/- 1.3 microM; Vmax, 0.17 +/- 0.01 nmol X mg protein-1 X min-1) and 6 wk (low-affinity system: Km, 271.7 +/- 17.5 microM; Vmax, 4.69 +/- 0.23 nmol X protein-1 X min-1; and high-affinity system: Km, 10.6 +/- 4.2 microM; Vmax, 0.16 +/- 0.09 nmol X mg protein-1 X min-1). These kinetic data suggest that the hyperplastic response in adapting proximal small bowel after distal resection is accompanied by a persistence of the membrane functional characteristics for both sodium-dependent D-glucose transport systems despite an altered pattern of enterocyte proliferation and differentiation.

Effect of monoclonal antibodies to enteroglucagon on ileal adaptation after proximal small bowel resection

On the basis of circumstantial clinical and experimental evidence, it has been suggested that enteroglucagon (EG) may act as an enterotrophic factor. This study was undertaken to evaluate the effects of long term in vivo immunoneutralisation of EG, using monoclonal antibodies to EG, on the hyperplastic ileal response after small bowel resection. Nineteen rats had a 70% proximal resection. A group of 10 rats was given iv 0.5 ml of undiluted hybridoma ascites immediately after the operation and on the 7th day postoperatively. Furthermore 0.025 ml/day of the same hybridoma ascitic fluid was continuously delivered ip for 14 days via mini-osmotic pumps. The hybridoma ascites was prepared from the clone 23.6B4 synthesising a monoclonal antibody directed toward the N-terminal to central region of the glucagon molecule which showed a marked crossreaction with EG. A control group of 9 rats was given a corresponding amount of antibody-free plasmacytoma ascites (Ag 8.653) by the same technique. Seven and 14 days postoperatively there was a plasma anti-EG-antibody excess with an excess binding capacity of 84.9 glucagon eq nM and 88.5 glucagon eq nM respectively. The three dimensional architecture and the proliferative activity of the ileal remnant were evaluated two weeks postoperatively. Despite a continuous immunoneutralisation of circulating endogenous EG by monoclonal antibodies, the adaptive response of the ileal remnants was of the same magnitude as that seen in the control group. These data do not support the hypothesis that EG is a circulating enterotrophic regulatory peptide.

Amino acid absorption in jejunum of rats in vivo--a kinetic comparison of distal resection effects

Jejunal absorption of leucine and cycloleucine by sham and 50% distal resected rats in vivo was studied by measuring the passive component and the active transport. After 5 months postresection the total amino acid absorption was increased. The mass-transfer coefficients of the passive process (obtained in presence of methionine) were higher in remnant jejunum than that in control rats, whereas the active transport remained unaltered after resection. When the kinetic constants of the saturable and non-saturable components were corrected for the unstirred water layer effects, the "real KD" increased in the resected group, whilst similar values for the "real Km and Jmax" were obtained.

Kinetics of phenylalanine absorption by the rat intestine in vivo after distal resection

The kinetics of L-phenylalanine absorption across rat small intestine in sham and 50% distal resected animals, in vivo, have been studied by perfusing jejunal loops and monitoring the disappearance of the substrate from the perfusate. After 5 months postresection the total phenylalanine absorption was increased. The relationship between total absorption of substrate and its concentration in the bulk phase shows a non-saturable component and a saturable one that can be inhibited by methionine, both in control and remnant jejunum. The slope of the line that represents the non-saturable component is greater in remnant jejunum, indicating that the apparent mass-transfer coefficient, K'D, was increased by distal resection. The kinetic analysis of the saturable component shows that Jmax was unaltered and the apparent semisaturation constant, K'M, was slightly decreased by distal small intestine resection. Correction of the kinetic constant for the unstirred water layer effects shows that the differences between 'real' KD values of the two experimental groups increase whereas 'real' KM values do not change significantly. This indicates that the observed increase in total intestinal absorption in resected animals appears to result from an increase in the intestinal passive permeability.

Early ultrastructural adaptive changes of ileal enterocytes after proximal small bowel resection as determined morphometrically

The aim of the present study was to evaluate in terms of quantitative measurements whether the well-known histomorphological and functional adaptive changes in the intestinal mucosa after small bowel resection are accompanied by alterations on the ultrastructural level. Therefore, samples of the ileal remnants after a 60% proximal resection were processed for ultrastructural evaluation and analyzed employing point counting planimetry and direct measurements. Microvillus surface area increased from the bottom of the crypts to the villus tips in both resected and sham-operated animals. This increase in microvillus surface area from the crypt to the villus was significantly less pronounced after proximal resection, while there were no changes in the crypt compartment. No significant differences of the relative areas of the nuclei, mitochondria, and the rough endoplasmic reticulum were observed when comparing the different positions along the villus crypt axis in normal and hyperplastic mucosa. In agreement with functional and enzyme histochemical results, these ultrastructural findings provide further evidence for an altered pattern of enterocyte maturation after proximal resection, which is most probably due to an increase in the migration rate of the enterocytes.

Absorption studies after massive small bowel resection and antiperistaltic colon interposition in rhesus monkeys

An experimental model of massive (80%) small bowel resection and antiperistaltic colon interposition in between the remnant jejunum and ileum was created in rhesus monkeys. The gastrointestinal functions were assessed preoperatively and at different periods after the operation. Progressive increase in the transit time and enhanced absorption of D-xylose and vitamin B12 was observed in these animals. The transit time marginally increased till three months postoperatively, and a significant increase was observed later (4-12 months) in the colon autografted monkeys. After three months, the D-xylose absorption in the colon interpositioned animals was nearly equal to that of normal monkeys. There was no significant difference in the vitamin B12 absorption in the normal and operated animals up to three months, but a significant rise was observed in the latter group after this period. The fecal fat excretion was 33-44% initially, and it gradually decreased to near normal values after nine months. The antiperistaltic colon interposition was effective in improving the early postoperative survival in animals after massive small bowel resection and enhanced the bowel absorption considerably.

Adaptation to jejunoileal bypass promotes experimental colorectal carcinogenesis

The co-carcinogenic potential of 85 per cent jejunoileal bypass (JIB) was tested in male Sprague-Dawley rats (n = 81) given 6 preliminary injections of the selective intestinal carcinogen azoxymethane (total dose 90 mg/kg). Controls had sham JIB. Colorectal adaptation was studied 30 weeks postoperatively in rats given injections of vehicle alone. JIB caused 17-33 per cent increments in colonic length, weight and crypt depth; crypt cell production rate was more than doubled (P less than 0.01). Despite lowering body weight by 27 per cent, JIB increased the median number of colorectal tumours per rat from 3 to 8 (P less than 0.01). The findings suggest that evidence of hyperplasia and dysplasia should be sought in patients receiving subtotal jejunoileal bypass for obesity.

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.

Enzymatic activities in jejunal biopsy specimens from patients with the stagnant-loop syndrome

The activity of the marker enzymes lactase, sucrase, neutral alpha-glucosidase, alkaline phosphatase, gamma-glutamyl transferase, leucyl-beta-naphthylamidase (brush border); 5-nucleotidase (basolateral membrane); and acid phosphatase and N-acetyl-beta-glucosaminidase (lysosomes) in jejunal biopsies from patients with the stagnant-loop syndrome and controls was studied. The activity of gamma-glutamyl transferase was increased in the patient group; the activity of the other enzymes did not differ significantly in patients and controls. The DNA to protein ratio was increased in the patient group. The results do not support the hypothesis of epithelial damage in the human stagnant-loop syndrome.

Jejunal mucosal enzymes in untreated and treated coeliac disease

A series of marker enzymes for brush borders, basolateral membrane, and lysosomes were assayed in mucosal biopsy specimens from patients with untreated and treated coeliac disease and from controls. The brush border enzymes lactase, sucrase, neutral alpha-glucosidase, alkaline phosphatase, and leucyl-beta-naphthylamidase showed reduced activities in the untreated state and complete or partial normalization during treatment. The lysosomal marker enzyme acid phosphatase increased in activity in untreated coeliac disease and was normalized by treatment. The brush border enzyme gamma-glutamyl transferase was nearly normal in untreated patients and slightly increased in treated patients. The basolateral membrane marker, 5'-nucleotidase, was reduced both in untreated and treated patients, whereas the lysosomal marker N-acetyl-beta-glucosaminidase was normal in the untreated state and decreased during treatment. The possible pathogenetic role of the three latter enzymes in coeliac disease is discussed. The patterns of the other enzymes are suggested to be attributable to the morphologic changes in the mucosa.

Cellular adaptation of amino acid transport following intestinal resection in the rat

1. The ability of rat ileal enterocytes to take up alanine and lysine before and after proximal resection of the small intestine has been assessed using both autoradiographic and dual-isotope methods of analysis. 2. The length of individual villi was approximately doubled after resection. Alanine uptake measured in the presence or absence of Na, represented per cm2 mucosal surface area, decreased following intestinal resection. 3. Alanine and lysine uptake were confined to villus tip enterocytes in both control and ileal remnants. The net effect of intestinal resection was to increase amino acid uptake calculated per individual villus or per unit length of intestine. 4. Adaptational changes occurring as a result of resection included a shortening of the time needed for enterocytes to reach the stage where they first began to absorb amino acids and a doubling of the rate at which absorption increased during the later stages of enterocyte differentiation. 5. It is suggested that the physiological response to intestinal resection can best be appreciated by studying events taking place within individual enterocytes. The way in which adaptational changes become organized within the mucosa remains to be elucidated.

Structural and functional correlations in the hypertrophic mucosa of intestinal remnants following resection in rats

Microdissection techniques were applied to determine the absolute increase in villus size and absorptive surface in the mucosa of rat intestinal remnants 3 weeks after 60% proximal resection. Adjacent tissues were used to evaluate the operational kinetic parameters describing the influx of L-phenylalanine and alpha-methyl-D-glucoside into intestinal rings. The villi of ileal remnants were enlarged significantly in all dimensions; the mean surface area of the villus was 2.5 times, and mucosal:serosal surface ratio 1.9 times larger than normal. The influx of phenylalanine and alpha-methyl-glucoside into the mucosa of ileal remnants was reduced, but the change could not be ascribed to an attenuation of one specific kinetic parameter. Using the microdissection data to transform the Vmax-values to a mucosal area basis, we could demonstrate that the Vmax for both substrates was smaller than normal. The results may derive from changes in the maturity of the cell population in intestinal remnants.

Three-dimensional structure and cell kinetics at different sites of rat intestinal remnants during the early adaptive response to resection

In this study the early phase of the morphological adaptation of rat ileum after a proximal resection of 60% has been studied using microdissection and cell labelling techniques. Resected rats and sham-operated controls were killed 2, 4, 6, 10 and 12 days after surgery. Intraperitoneal injections of 3H-thymidine were carried out 24 or 12 h prior to sacrifice. In the latter groups mitotic arrest was achieved by vincristine. A stereo-microscope was used to measure and calculate the following parameters: intestinal diameter; villus: height, width, breadth at base and apex, surface, enterocytes per 100 micrometers length, cell pool, number of villi and absorptive surface per mm2 serosal area; crypt: length, enteroblasts per 100 micrometers length and per column, cell columns and mitoses per crypt, cell pool, crypts, and mitoses per unit serosal area; cell kinetics: migration rate, villus transit time. To test the influence of treatments, postoperative time course and the location of the intestinal segment and their possible interactions, factorial analyses of variance were carried out on the parameters investigated. The main findings, demonstrated for the first time, were: 1. An increase in the villus surface which was achieved by proportional enlargement of villus geometry; 2. This increase in the villus surface led to an enlarged absorptive surface per unit serosal area; 3. A reduction of villus transit time of the individual enterocyte; 4. A most pronounced magnitude of adaptative response in the proximal remnants which was gradually diminished in aboral direction, and 5. A sequential course of adaptative response of the various crypt parameters investigated.

Effects of aromatic retinoid on non-keratinizing (intestinal) epithelium: biochemical and morphological studies

Doses of 3 mg/kg Ro 10-9359 (in arachis oil) were daily administered to adult female Wistar rats by gastric tube for a period of 10 days. Control animals received corresponding quantities of arachis oil only. The body weight of all rats was registered daily. Samples of jejunum and ileum were processed for quantitative histochemical analysis of neutral alpha-glucosidase kinetics and for three-dimensional evaluation of the mucosal architecture. In addition, mucosal scrapings were prepared from these intestinal segments, and the specific sucrase activity was determined. For each animal data were pooled and analyzed by Wilcoxon (Wn) test. Body weight and all registered parameters in the jejunum of treated animals remained unchanged as compared to the controls. In the ileum, however, we found under aromatic retinoid an increase of sucrase activity (P = 0.02) and of mucosal surface per unit serosal area (P less than 0.05). The hydrolytic activity of neutral alpha-glucosidase (Vmax) showed a clear trend to increase at both the villus base and apex, whereas the apparent substrate affinity (Km) remained unaltered. Our results show that, in closes of 3 mg/kg/day, aromatic retinoid induces (1) an increase in mucosal surface area, apparently due to hyperproliferation of the absorptive epithelium in ileum, which could facilitate its absorptive capacity and (2) an increase of specific sucrase activity, which could result in an enhanced carbohydrate assimilation. These findings indicate that Ro 10-9359 in addition to its effects on keratinizing epithelia exerts a distinct influence on the structure and function of the intestinal epithelium.