Proximal enterectomy provides a stronger systemic stimulus to intestinal adaptation than distal enterectomy

Adaptation Processes of the Remaining Jejunum or Ileum after Extensive Intestinal Resection

PURPOSE

To compare the adaptation processes of the remaining jejunum or ileum after extensive intestinal resection in a growing animal model.

MATERIALS AND METHODS

Forty 21-day old rats were divided into four groups: JG: remaining jejunum group - ileal enterectomy; IG: ileum remaining group - jejunum enterectomy; SHAM: sham-operated group - open-and-close laparotomy; and NO: non-operated animals.

RESULTS

After 3 weeks, JG and IG animals had decreased weights comparing to SHAM and NO animals (p = 0.017 and p = 0.005, respectively). The histomorphometric analysis showed that in JG animals the villi were higher than in SHAM, NO, and IG animals (p = 0.007, p = 0.008, and p = 0.01), the depth of crypts in JG and IG animals was greater than in NO and SHAM animals (p = 0.03, p = 0.002, and p = 0.003 respectively), and muscle layer thickness of the jejunum of JG animals had values greater than SHAM and NO animals (p = 0.01 and p = 0.02, respectively). The Ki-67 expression in the ileum was higher in comparison with the jejunum (p = 0.014). The pro-apoptotic gene (Bax) expression was decreased in JG animals compared to IG, SHAM, and NO animals (p = 0.013, p = 0.024, and p = 0.021). The anti-apoptotic gene (Bcl-XL) expression was decreased in JG animals in comparison to IG and NO animals (p = 0.002 and p = 0.046) although it was increased in the colon of IG animals in comparison to JG, SHAM, and NO animals (p = 0.002, p = 0.001, and p = 0.001, respectively). The Bax/Bcl-XL ratio was higher in JG than in IG animals (p = 0.011).

CONCLUSION

Adaptive responses seemed to be more effective in the ileum than in the jejunum.

In the Short-term, Milk Fat Globule Epidermal Growth Factor-8 Causes Site-specific Intestinal Growth in Resected Piglets

OBJECTIVES

Short bowel syndrome (SBS) remains the leading cause of neonatal intestinal failure. Milk fat globule epidermal growth factor-8 (MFG-E8), present in human milk, has homology with epidermal growth factor (EGF), known to enhance adaptation in SBS. In this pilot study, the role of oral MFG-E8 treatment in SBS was explored in neonatal piglets.

METHODS

Neonatal piglets underwent 75% intestinal resection, either distal (jejunal-colonic [JC] anastomosis) or mid-intestinal (jejunal-ileal [JI] anastomosis). Piglets were randomized to intragastric treatment with MFG-E8  (5 mg/kg per day) or saline and were maintained on parenteral nutrition and enteral nutrition for 7 days. Adaptation was assessed by intestinal length and weight, histopathology, fecal fat analysis and RT-qPCR analysis of mucosal transcripts, including growth factors.

RESULTS

JI piglets demonstrated intestinal lengthening (P < 0.001), 2-fold greater in ileum than jejunum (P = 0.02), where lengthening was increased by MFG-E8 treatment (P = 0.02). JC piglets did not exhibit jejunal lengthening, regardless of treatment. Fat absorption was greater for JI piglets (P = 0.02), unaffected by treatment. In JI piglets, expression of Egf was increased in the ileum (P < 0.01) and MFG-E8 treatment increased Egfr (receptor) expression (P = 0.02).

CONCLUSIONS

MF-EG8 demonstrated site-specific trophic effects, only with JI anatomy. This may limit the utility of this treatment for SBS, except for rare patients with retained ileum. The mechanisms of these site-specific effects, however, and the role of MFG-E8 in neonatal gut growth and in diseases, such as necrotizing enterocolitis that commonly target ileum, warrant further exploration.

The 5-HT4 Receptor Agonist Prucalopride Stimulates Mucosal Growth and Enhances Carbohydrate Absorption in the Ileum of the Mouse

BACKGROUND

Enteric serotonin may function as a mucosal growth factor. Previous work demonstrated increased crypt cell proliferation and intestinal mucosal surface area with potentiation of serotonin. While an indirect mechanism was postulated to explain these effects, the presence of 5-HT4 receptors on enterocytes raises the possibility of a direct action of serotonin. We hypothesized that a 5-HT4 specific agonist, prucalopride, would stimulate intestinal mucosal growth and enhance absorptive function in the murine small intestine.

METHODS

Adult wild-type mice were treated parenterally with prucalopride for 14 days via surgically implanted osmotic pumps. In vivo D-xylose absorption was assessed by oral gavage and serum D-xylose measurements. On day 14, glucose absorption was assessed by instilling a glucose solution into isolated segments of small intestine. The bowel was harvested and examined for morphologic parameters and crypt cell proliferation.

RESULTS

Villus height, crypt depth, and crypt proliferation were significantly increased in the distal small bowel of prucalopride-treated mice compared with control animals. Crypt depth was also increased in the proximal and middle small intestine in treated mice. There was no difference in D-xylose absorption throughout the study period; however, glucose absorption was significantly increased in the distal small intestine of prucalopride-treated mice.

CONCLUSION

Parenteral administration of the 5-HT4 receptor specific agonist, prucalopride, results in morphologic and functional changes in the murine small intestine that are most prominent in the distal small bowel. While further studies are necessary to delineate the mechanism, it is plausible that the effects are mediated by 5-HT4 receptors on enterocytes.

A detailed guide to lipid therapy in intestinal failure

Intravenous lipid emulsions are an integral part of nutrition therapy in the intestinal failure patient. In addition to being a concentrated source of non-protein calories, they provide the essential fatty acids necessary for growth and development. Depending upon the oil source used in these products, complications such as intestinal failure associated liver disease (IFALD) can occur. This review will discuss the risks and benefits associated with these products, especially as they relate to the pediatric intestinal failure patient.

Distinct intestinal adaptation for vitamin B12 and bile acid absorption revealed in a new mouse model of massive ileocecal resection

Ileocecal resection (ICR), one of several types of intestinal resection that results in short bowel syndrome (SBS), causes severe clinical disease in humans. We here describe a mouse model of massive ICR in which 75% of the distal small intestine is removed. We demonstrate that mice underwent 75% ICR show severe clinical signs and high mortality, which may recapitulate severe forms of human SBS, despite an adaptive response throughout the remnant intestine. By using this model, we also investigated whether the epithelium of the remnant intestine shows enhanced expression of factors involved in region-specific functions of the ileum. Cubn mRNA and its protein product, which play an essential role in vitamin B12 absorption in the ileum, are not compensatory up-regulated in any part of the remnant intestine, demonstrating a clear contrast with post-operative up-regulation of genes involved in bile acid absorption. Our study suggests that functional adaptation by phenotypical changes in the intestinal epithelium is not a general feature for nutrient absorption systems that are confined to the ileum. We also propose that the mouse model developed in this study will become a unique system to facilitate studies on SBS with ICR in humans.

Summary: Genes involved in region-specific functions of the distal small intestine show distinct adaptive response following massive ileocecal resection in mice.

A potential anatomic subtype of short bowel syndrome: a matched case-control study

Background

Fundamental researches suggest that ileum presents greater adaptive potential than the jejunum. However, few studies estimate the association between ileum and adaptive potential in human. To discover the association, we conducted this matched case-control study.

Methods

A 1:2 pair-matched, case-control study was conducted from January 1, 2001 to January 1, 2015 in Intestinal Rehabilition and Transplant Center. The case group was ileum predominated (IP) group and the control group was jejunum predominated (JP) group. Demographic data, medical history and progression of each patient were collected.

Results

There were 24 IP cases and 48 JP controls in this study. The cumulative probabilities of parenteral nutrition (PN) weaning in IP group were higher than that in JP group. The Bristol stool scale scores of IP group were lower than that of JP group at third month. The Cox proportional hazards regression model confirmed that IP had a higher odds of PN weaning (OR = 2.69; 95 % CI: 1.27, 5.70, p = 0.01) as compared with JP group. The conditional logistic regression with 1:2 matching also confirmed IP group had a higher odds (OR = 4.84; 95 % CI: 2.02, 11.56, p <0.01).

Conclusions

Our results indicated that ileum presents greater adaptive potential than the jejunum in nutrition and fluid absorption. And a potential anatomic subtype of short bowel syndrome was proposed. Further research need to be conducted to more fully understand the adaptive potential of ileum besides nutrition and fluid absorption.

Intestinal adaptation following resection

Intestinal adaptation is a natural compensatory process that occurs following extensive intestinal resection, whereby structural and functional changes in the intestine improve nutrient and fluid absorption in the remnant bowel. In animal studies, postresection structural adaptations include bowel lengthening and thickening and increases in villus height and crypt depth. Functional changes include increased nutrient transporter expression, accelerated crypt cell differentiation, and slowed transit time. In adult humans, data regarding adaptive changes are sparse, and the mechanisms underlying intestinal adaptation remain to be fully elucidated. Several factors influence the degree of intestinal adaptation that occurs post resection, including site and extent of resection, luminal stimulation with enteral nutrients, and intestinotrophic factors. Two intestinotrophic growth factors, the glucagon-like peptide 2 analog teduglutide and recombinant growth hormone (somatropin), are now approved for clinical use in patients with short bowel syndrome (SBS). Both agents enhance fluid absorption and decrease requirements for parenteral nutrition (PN) and/or intravenous fluid. Intestinal adaptation has been thought to be limited to the first 1-2 years following resection in humans. However, recent data suggest that a significant proportion of adult patients with SBS can achieve enteral autonomy, even after many years of PN dependence, particularly with trophic stimulation.

Neonatal intestinal physiology and failure

The neonatal intestine is a complex organ that regulates the absorption of nutrients essential for growth and development. Intestinal failure results from insufficient or functionally inadequate bowel and can lead to failure of neonatal growth and development. Current literature on neonatal intestinal physiology and failure was reviewed and summarized. A homeostatic interplay of electrolytes, enzymes, and hormonal regulators is essential to achieve the physiologic balance needed for adequate intestinal performance. Physiologic consequences of intestinal failure are dependent on the length and anatomic location of the diseased or surgically resected bowel. Intestinal failure leads to disruption of normal intestinal physiology and may have long-term consequences for growth and development if inadequately treated. Parenteral nutrition remains the mainstay of treatment for neonatal intestinal failure.

Short-term adaptation of rat intestine to ileostomy: implication for pediatric practice

BACKGROUND

Surgical neonates with complex intestinal conditions, such as enterocolitis, midgut volvulus with bowel loss and multiple atresias, often require temporary stomas. Little is known on the postsurgical response of the altered gut segments, although adaptation is an important consideration in neonatal postoperative care, particularly after stoma closure.

MATERIALS AND METHODS

Rats underwent bowel resection at a point 15 cm proximal to the ileocecal valve, and a split ileostomy was performed. On the 6th postoperative day the mucosal thickness was calculated with Soft Imaging System Analysis Pro, the rate of proliferation was measured following Ki67 immunohistochemistry and the apoptotic index was determined on sections stained with ApopTag Plus. The intestinal motor activity was recorded on isolated gut segments. Neuronal nitric oxide synthase (nNOS) expression and distribution was examined with NADPH-diaphorase histochemistry and Western blot analysis.

RESULTS

An increased wet weight of the mucosa and a pronounced mucosal thickening were observed in the proximal functional bowel segment. Enterocyte proliferation rate was increased significantly, while the apoptotic index remained unchanged in the epithelial layer. The dilation of the gut lumen resulted in a morphological change in the nitrergic myenteric network with an overexpression of nNOS. As a consequence of the surgical procedure, the functional proximal gut segment showed strong and frequent contraction waves, with an enhanced responsiveness to cholinergic stimuli.

CONCLUSIONS

The dilated functional bowel segment was characterized by hyperplasic changes in the mucosa and stronger mechanical activity with overproduction of nNOS. Although early restoration of intestinal continuity is recommended, our observations on adaptive changes may partly explain intestinal motility disorders after early stoma closure, suggesting the need for a careful approach to a redo-laparotomy.

Expansion of intestinal stem cells associated with long-term adaptation following ileocecal resection in mice

Sustained increases in mucosal surface area occur in remaining bowel following massive intestinal loss. The mechanisms responsible for expanding and perpetuating this response are not presently understood. We hypothesized that an increase in the number of intestinal stem cells (ISC) occurs following intestinal resection and is an important component of the adaptive response in mice. This was assessed in the jejunum of mice 2-3 days, 4-5 days, 6-7 days, 2 wk, 6 wk, and 16 wk following ileocecal resection (ICR) or sham operation. Changes in ISC following ICR compared with sham resulted in increased crypt fission and were assayed by 1) putative ISC population (SP) by flow cytometry, 2) Musashi-1 immunohistochemistry, and 3) bromodeoxyuridine (BrdU) label retention. Observed early increases in crypt depth and villus height were not sustained 16 wk following operation. In contrast, long-term increases in intestinal caliber and overall number of crypts per circumference appear to account for the enhanced mucosal surface area following ICR. Flow cytometry demonstrated that significant increases in SP cells occur within 2-3 days following resection. By 7 days, ICR resulted in marked increases in crypt fission and Musashi-1 immunohistochemistry staining. Separate label-retention studies confirmed a 20-fold increase in BrdU incorporation 6 wk following ICR, confirming an overall increase in the number of ISC. These studies support that expansion of ISC occurs following ICR, leading to an overall increase number of crypts through a process of fission and intestinal dilation. Understanding the mechanism expanding ISCs may provide important insight into management of intestinal failure.

Intestinal epithelial cell proliferation is dependent on the site of massive small bowel resection

Early intestinal adaptation after massive small bowel resection (SBR) is driven by increased epithelial cell (EC) proliferation. There is a clear clinical difference in the post-operative course of patients after the loss of proximal (P) compared to distal (D) small bowel. This study examined the effects of the site of SBR on post-resectional intestinal adaptation, and investigated the potential mechanisms involved. C57BL/6J mice (n = 7/group) underwent: (1) 60% P-SBR, (2) 60% D-SBR, (3) 60% mid (M)-SBR and (4) SHAM-operation (transection/reanastomosis). Mice were sacrificed at 7 days after surgery and ECs and adjacent mucosal lymphocytes (IELs) isolated. Adaptation was assessed in both jejunum and ileum by quantification of villus height, crypt depth, villus cell size, crypt cell size (microns), goblet cell number, and EC proliferation (%BrdU incorporation). Proliferation signalling pathways including keratinocyte growth factor (KGF)/KGFR(1), IL-7/IL-7R, and epidermal growth factor receptor (EGFR) were measured by RT-PCR. Expression of IL-7 was further analysed by immunofluorescence. Data were analyzed using ANOVA. All three SBR models led to significant increases in villus height, crypt depth, goblet cell numbers and EC proliferation rate when compared to respective SHAM groups. The strongest morphometric changes were found for jejunal segments after M-SBR and for ileal segments after P-SBR. Furthermore, morphometric analysis showed that at 1-week post-resection a tremendous increase in EC numbers occurred in jejunal villi (cell hyperplasia), whereas a significant increase in EC size predominated in ileal villi (cell hypertrophy). mRNA expression of KGF, KGFR(1), IL-7R, and EGFR showed a significant increase only after D-SBR, whereas IL-7 increased significantly after SBR in all investigated models, and this was confirmed by immunofluorescence studies. Early intestinal adaptation shows distinct differences depending on the site of SBR, and is predominately driven by cell hyperplasia in jejunal villi and cell hypertrophy in ileal villi. However, the exact mechanisms, which guide these signalling pathways are still unclear.

The effect of biliary sphincterotomy on serum cholesterol level in postcholecystectomy patients: a pilot study

BACKGROUND

Cholesterol, in the form of bile salts, is reabsorbed from the small intestine via the enterohepatic circulation. Biliary sphincterotomy increases the delivery of bile to the terminal ileum. If the absorptive capacity is exceeded, cholesterol excretion may increase, resulting in a decrease in serum cholesterol levels and improvement in serum lipid profiles.

AIM

To determine the effect of biliary sphincterotomy on serum cholesterol levels in patients without biliary obstruction.

PATIENTS AND METHODS

Postcholecystectomy patients with type III biliary sphincter of Oddi dysfunction (disabling pancreatobiliary-type pain with normal liver function tests and bile duct diameter) who underwent biliary sphincterotomy were identified retrospectively from the endoscopic retrograde cholangiopancreatography database. Baseline (pre-endoscopic retrograde cholangiopancreatography) laboratory investigations (including cholesterol) were obtained for all patients. The effect of sphincterotomy on total cholesterol levels was noted in all patients who returned for subsequent procedures (temporary pancreatic stent removal or evaluation of recurrent symptoms), and also in the subgroup of patients with baseline hypercholesterolemia (higher than 5.18 mmol/L).

RESULTS

In the present pilot study, the performance of biliary sphincterotomy was associated with a reduction in total serum cholesterol levels in postcholecystectomy patients without biliary obstruction. This was statistically significant in patients with a baseline cholesterol level higher than 5.18 mmol/L. A possible effect on low- and high-density lipoprotein concentrations was not evaluated. The influence of dietary changes and exercise were not accounted for.

CONCLUSION

A prospective, controlled study involving a larger series of patients is required to determine whether biliary sphincterotomy lowers cholesterol levels and improves lipid profiles.

Influence of the site of small bowel resection on intestinal epithelial cell apoptosis

Massive small bowel resection (SBR) results in a significant increase in intestinal epithelial cell (EC) proliferation as well as apoptosis. Because the site of SBR (proximal (P) vs. distal (D)) affects the degree of intestinal adaptation, we hypothesized that different rates of EC apoptosis would also be found between P-SBR and D-SBR models. Wild-type C57BL/6J mice underwent: (1) 60% P-SBR, (2) 60% D-SBR, or (3) SHAM-operation (transaction-reanastomosis) at the mid-gut point. Mice were sacrificed after 7 days. EC apoptosis was measured by TUNEL staining. EC-related apoptotic gene expression including intrinsic and extrinsic pathways was measured with reverse transcriptase-polymerase chain reaction. Bcl-2 and bax protein expression were analyzed by Western immunoblotting. Both models of SBR led to significant increases in villus height and crypt depth; however, the morphologic adaptation was significantly higher after P-SBR compared to D-SBR (P<0.01). Both models of SBR led to significant increases in enterocyte apoptotic rates compared to respective sham levels; however, apoptotic rates were 2.5-fold higher in ileal compared to jejunal segments (P<0.01). P-SBR led to significant increases in bax (pro-apoptotic) and Fas expression, whereas D-SBR resulted in a significant increase in TNF-alpha expression (P<0.01). EC apoptosis seems to be an important component of intestinal adaptation. The significant difference in EC apoptotic rates between proximal and distal intestinal segments appeared to be due to utilization of different mechanisms of action.

Bax is required for resection-induced changes in apoptosis, proliferation, and members of the extrinsic cell death pathways

BACKGROUND AND AIMS

To define better the homeostatic mechanisms contributing to small intestinal adaptation following partial resection, the relative contributions of apoptosis, cell proliferation, and enterocyte migration and the comparative roles of the intrinsic (mitochondrial) and extrinsic (death receptor-mediated) apoptotic pathways were assessed.

METHODS

After 50% jejunoileal resections or transections, adaptation was analyzed in duodenal-jejunal and ileal segments from C57BL/6 Bax(+/+) (16, 48, and 168 hours postoperative) and Bax(-/-) mice (168 hours).

RESULTS

Basal apoptotic rates were equivalent in all mice. By 1-week postresection, villus heights and crypt depths were increased in the duodenal-jejunal and ileal remnants of both genotypes. In Bax(+/+) mice, adaptation occurred in concert with increased crypt proliferative and apoptotic indices. Bax(-/-) mice did not show increases in proliferation or apoptosis, yet adaptive increases in villus height were enhanced relative to Bax(+/+) mice. Enterocyte migration increased in both genotypes. Postresection, the expression of caspases and genes involved in death receptor-mediated apoptosis was decreased in Bax(-/-) compared with Bax(+/+) mice.

CONCLUSIONS

Postresection adaptation involves parallel changes in crypt proliferation and apoptosis, but, as observed in Bax(-/-) mice, it can occur without increased proliferation. These studies demonstrate that spontaneous gut apoptosis is Bax independent, whereas adaptation-related apoptosis is Bax-dependent. Differences between resected Bax(+/+) and Bax(-/-) mice suggest that apoptosis in the adapting gut utilizes the extrinsic pathway, but this requires linkage to the mitochondrial pathway via Bax. The increased adaptive response in Bax(-/-) mice indicates that modulation of apoptosis may be useful for enhancing adaptation.

Time-dependent intestinal adaptation and GLP-2 alterations after small bowel resection in rats

Existing data on morphological adaptation after small bowel resection are obtained by potentially biased methods. Using stereological techniques, we examined segments of bowel on days 0, 4, 7, 14, and 28 after 80% jejunoileal resection or sham operation in rats and correlated intestinal growth with plasma levels of glucagon-like peptide-2 (GLP-2). In the jejunum and ileum of the resected rats, the mucosal weight increased by 120 and 115% during the first week, and the weight of muscular layer increased by 134 and 83%, compared with sham-operated controls. The luminal surface area increased by 190% in the jejunum and by 155% in the ileum after 28 days. The GLP-2 level was increased by 130% during the entire study period in the resected rats. Small bowel resection caused a pronounced and persistent transmural growth response in the remaining small bowel, with the most prominent growth occurring in the jejunal part. The significantly elevated GLP-2 level is consistent with an important role of GLP-2 in the adaptive response.

Intestinal regrowth is amplified after jejunal but not ileal resection during tapeworm infection in the rat

The ileum possesses functions required by a healthy individual that are not fully supplanted by the duodenum or jejunum. Evidence suggests that the ileum may also be necessary to maintain an enteric parasite-host interaction. We hypothesized that the ileum is essential to the survival of the lumen-dwelling, rat tapeworm, H. diminuta. Male rats were divided into three groups: those with ileal or jejunal resections and nonresected controls. Half of each rat group was infected with the tapeworm. After jejunal resection, the weight but not length of intestinal remnant (duodenum + ileum) in infected rats returned to that of control, nonresected intestine 29 days after surgery and tapeworm numbers were fully maintained. In contrast, after ileal removal intestinal length and weight of the remaining duodenum and jejunum in infected rats were significantly decreased and tapeworm survival diminished. Data indicates that intestinal growth following resection is amplified by tapeworm infection when the ileum remains but diminished when the ileum is removed. Furthermore, loss of the ileum results in decreased infection intensity and dry weight of the tapeworm.

Ileal absorptive adaptation to jejunal resection and extrinsic denervation: implications for living-related small bowel transplantation

Net absorption of water, electrolytes, and simple nutrients decreases early after jejunoileal autotransplantation (extrinsic denervation) in a canine model but recovers toward normal by 8 weeks. However, the ability of the extrinsically denervated ileum to adapt after total jejunectomy, which would be relevant as a model of segmental small bowel transplantation, remains unknown. Two groups of five dogs each were studied before and 2 weeks and 12 weeks after 50% proximal enterectomy. A control group remained neurally intact, whereas the other group underwent extrinsic denervation (Ext Den) of the remaining ileum. Using a perfusion technique, net absorption of water, electrolytes, and five simple nutrients (glucose, arginine, glutamine, and oleic and taurocholic acids) was measured at the three time points. Ileal morphometry was also evaluated. All dogs developed diarrhea, which resolved by 12 weeks in all but two of the Ext Den dogs. Weight in both groups was decreased at 2 weeks (P <0.05), returned to normal at 12 weeks in control dogs, but remained low in Ext Den dogs (P <0.05). Maximal weight loss was greater in the Ext Den group (P <0.05). No consistent or important differences in net absorptive fluxes of water, electrolytes, or simple nutrients were noted either within or between groups at any time point. Villous height, crypt depth, and longitudinal muscle width increased significantly at 12 weeks after jejunectomy in the Ext Den dogs, but not in the control dogs (P <0.05). Extrinsic denervation of the ileum results in persistent weight loss after proximal 50% enterectomy. Despite diarrhea, only minor changes in electrolyte absorption occur, and ileal net absorption of simple nutrients remains unaffected. The ileum of extrinsically denervated dogs undergoes a more prominent morphometric adaptation after jejunectomy. Extrinsic denervation necessitated by small bowel transplantation, independent of immune effects, does not appear to suppress the ileal adaptive response to maintain net absorption of water, electrolytes, and simple nutrients.

Effect of the distal remnant on ileal adaptation

The ileum has a greater adaptive capacity than the jejunum after intestinal resection, which may be, in part, related to increased exposure to luminal contents and intrinsic properties of the ileum However, the intestinal remnant might contribute to this adaptive response as well. Our aim was to determine the effect of the distal intestinal remnant on ileal adaptation when the ileum is proximal in the intestinal tract. Twenty-one Lewis rats were included in the study. One group (n = 7) served as unoperated control subjects, the second group (n = 7) underwent transposition of the jejunum and ileum, and the third group (n = 7) underwent 50% proximal resection with syngeneic transplantation of the ileum Nutritional status and structural adaptation were studied at 14 days. Animals in both the transposition and transplant groups initially lost weight but weights returned to above preoperative levels at 14 days. Food intake, stool weight, and serum albumin levels were similar in these two groups. Intestinal weight and diameter were similar in the proximal end of the ileal segment in the two study groups and were significantly increased compared to control values (0.26 +/- 0.04 and 0.31 +/- 0.02 vs. 0.10 +/- 0.0 g/cm and 8.4 +/- 0.5 and 9.1 +/- 0.8 vs. 4.9 +/- 0.3 mm; P < 0.05) Intestinal weight and diameter of the distal end of the ileal segment were greater than those values in unoperated control animals but were greatest in the ileal transplant group (0.15 +/- 0.1 and 0.24 +/- 0.03 vs. 0.07 +/- 0.01 g/cm and 5.6 +/- 1.1 and 8.7 +/- 0.6 vs. 4.3 +/- 0.2 mm; P < 0.05). Villus height and crypt depth were similar in both the proximal and distal ends of the ileal segments in the two study groups and were significantly increased compared to control values (642 +/- 75 and 720 +/- 15 vs. 411 +/- 24 proximal and 443 +/- 49 and 500 +/- 46 vs. 343 +/- 22 microm distal, P < 0.05; 223 +/- 34 and 244 +/- 33 vs. 173 +/- 20 proximal and 192 +/- 28 and 209 +/- 18 vs. 144 +/- 26 microm distal, P < 0.05). Proximal placement of the ileum by either transposition or transplantation results in structural adaptation. This occurs to a similar extent whether the distal remnant is jejunum or ileum. Thus increased exposure to luminal contents and intrinsic properties appear to be the important factors in the adaptive capability of the ileum when the ileum is the proximal portion of the intestinal tract.

Comparison of ileal and jejunal transplantation after 50% proximal intestinal resection

BACKGROUND

The ileum has a greater adaptive capacity than the jejunum after intestinal resection. Transposition studies suggest that this is, in part, related to increased exposure to nutrients. However, there may be regional differences in intestinal properties that contribute to this response as well. The aim of this study was to compare the outcome of replacing the jejunum with either ileal or jejunal transplants while preserving an intact ileum after 50% proximal resection.

METHODS

Twenty-one Lewis rats were included in the study. One group (n = 7) served as transection controls (TC). The other two groups (n = 7) had 50% proximal resection with syngeneic transplantation of a similar length of ileum (ITX) or jejunum (JTX). Nutritional status and adaptation were studied at 14 days.

RESULTS

JTX animals gained less weight than TC and ITX (104 +/- 2% vs 114 +/- 1 and 108 +/- 2% initial, P < 0.05). ITX and JTX groups had lower caloric intake and serum albumin levels compared with TC (7.4 +/- 0.4 and 7.2 +/- 0.8% vs 8.8 +/- 0.2% body weight and 2.6 +/- 0.1 and 2.4 +/- 0.9 g/dl vs 3.0 +/- 0.1 g/dl, P < 0.05). Mucosal thickness increased significantly in the ileal remnant of both ITX and JTX groups (9.2 +/- 2.1 and 8.8 +/- 0.6 micrometer vs 6.6 +/- 0.6 micrometer, P < 0.05). Transplanted ileum had mucosal thickness similar to that of jejunum.

CONCLUSIONS

Transplanted ileum achieves an intestinal structure similar to that of the jejunum in the same environment. Modest adaptation of the remnant occurs with transplantation. Replacing jejunum with ileum rather than jejunum resulted in better weight gain, suggesting that intrinsic absorptive, motor, or hormonal rather than structural differences are responsible.

Factors affecting outcome following proximal and distal intestinal resection in the dog: an examination of the relative roles of mucosal adaptation, motility, luminal factors, and enteric peptides

In the clinical setting, resection of the ileum results in an inferior functional outcome compared to jejunal resection. This may be related to a greater adaptive capacity of the ileum, intrinsic structural and functional differences, or regional differences in motor and hormonal function. Our aim was to evaluate the relative contributions of these factors to functional outcome after resection of the proximal or distal intestine. Twenty-four dogs underwent either intestinal transection or 50% resection of the proximal or distal intestine. Studies (nutritional status, absorption, adaptation, motility, peptide levels) were performed every four weeks until the animals were killed at 12 weeks. Caloric intake was similar in all four groups. Weight loss was greater and more sustained after distal resection (DR). Serum cholesterol levels decreased significantly only in the DR group. While stool weight and moisture were similar, the DR animals had persistent, significant steatorrhea. Intraluminal anaerobic bacteria and SCFA concentrations were significantly greater in the ileum but were not influenced by resection. Intestinal remnant length increased to a greater extent after proximal resection (PR), but circumference increased to a similar extent after both resections. Villus height and crypt depth increased significantly only after PR. MMC frequency was similar in all four groups. In the DR animals 26% of migrating motor complexes (MMCs) originated within the remnant. The jejunal remnant of these animals had a dominance of cluster activity similar to the intact distal ileum. Following PR, the postprandial motilin response was decreased. After DR, there were transient increases in neurotensin and PYY. Of the various factors evaluated, mucosal adaptation and the intestinal motor response appear most likely to explain the inferior nutritional and absorptive outcome associated with resection of the distal small intestine.

Smooth muscle adaptation after intestinal transection and resection

Changes in motor function occur in the intestinal remnant after intestinal resection. Smooth muscle adaptation also occurs, particularly after extensive resection. The time course of these changes and their interrelationship are unclear. Our aim was to evaluate changes in canine smooth muscle structure and function during intestinal adaptation after transection and resection. Twenty-five dogs underwent either transection (N = 10), 50% distal resection (N = 10), or 50% proximal resection (N = 5). Thickness and length of the circular (CM) and longitudinal (LM) muscle layers were measured four and 12 weeks after resection. In vitro length-tension properties and response to a cholinergic agonist were studied in mid-jejunum and mid-ileum. Transection alone caused increased CM length in the jejunum proximal to the transection but did not affect LM length or muscle thickness. A 50% resection resulted in increased length of CM throughout the intestine and thickening of CM and LM near the anastomosis. Active tension of jejunal CM increased transiently four weeks after resection. Active tension in jejunal LM was decreased 12 weeks after transection and resection. Sensitivity of CM to carbachol was similar after transection and resection. It is concluded that: (1) Structural adaptation of both circular and longitudinal muscle occurs after intestinal resection. (2) This process is influenced by the site of the intestinal remnant. (3) Only minor and transient changes occur in smooth muscle function after resection. (4) Factors other than muscle adaptation are likely involved in the changes in motor function seen following massive bowel resection.

Plasma enteroglucagon levels in different models of intestinal resection in the rat

To assess the influence of the different intestinal segments on the plasma enteroglucagon level, three models of intestinal resection in the rat were studied (jejunal, ileal, 90%). The basal values for this peptide and those obtained after an infusion of intraduodenal glucose were compared. The results obtained in basal/post-glucose infusion were: 50% proximal (jejunum): 220/728 pg/ml; 50% distal (ileum): 10/233 pg/ml; and the middle 90%: 108/297 pg/ml. The glucose infusion produced a maximal response, permitting a better evaluation of the differences among the three resection models. The highest levels corresponded to the group in which the entire ileum was conserved.

The motor response to intestinal resection: motor activity in the canine small intestine following distal resection

BACKGROUND

The mucosal response to intestinal resection has been extensively studied; little is known of the motor response. Our aim was to evaluate motility in the intestinal remnant following distal resection.

METHODS

Motor activity, duodenocecal transit, nutrition, and absorption were studied over a 3-month period in control animals (n = 9) and in groups of dogs who had undergone 25% (n = 6), 50% (n = 5), and 75% (n = 5) distal resection.

RESULTS

Diarrhea and steatorrhea developed in each resection group, and the 75% group alone developed true short bowel syndrome. Resection did not affect migrating motor complex frequency or periodicity; phase 1 duration was shorter in the 75% group (control vs. 75%: 22 +/- 4 vs. 6 +/- 2 minutes, P < 0.03). The most striking motor effect was the development of prominent cluster activity in the distal part of the remnant in 25% and 50% resection animals and throughout the remaining intestine in the 75% group. Duodenocecal transit slowed during the study period from 13 +/- 1 to 20 +/- 2 minutes in the 50% and from 10 +/- 2 to 14 +/- 2 minutes in the 75% group (P < 0.05).

CONCLUSIONS

The initial motor response to major resections of the distal small intestine is dominated by the development of abnormal patterns. This motor disruption may contribute to the symptomatology and clinical features of the short bowel syndrome.

Neurotensin augments intestinal regeneration after small bowel resection in rats

Massive small bowel resection (SBR) is characterized by increased proliferation of residual gut mucosa and pancreas. Neurotensin (NT), a gut tridecapeptide, stimulates growth of normal gut mucosa and pancreas. This study examined whether NT affected growth of the small intestine and the pancreas after either distal or proximal SBR. Male Fischer 344 rats were divided into four groups. Group 1 underwent ileal transection with reanastomosis (SHAM) and group 2 underwent 70% distal SBR. Group 3 underwent SHAM operation (jejunal transection), and group 4 underwent 70% proximal SBR. After operation, each group was further subdivided to receive either saline (control) or NT (300 micrograms/kg) subcutaneously in gelatin every 8 hours for 7 days. At death, the pancreas and proximal jejunum (from groups 1 and 2) or distal ileum (from groups 3 and 4) were removed, weighed, and analyzed for DNA, RNA, and protein content. Both proximal and distal SBR significantly increased mucosal growth in the remnant intestine; a more pronounced effect was noted with proximal SBR. Administration of NT significantly augmented the adaptive changes in both groups of rats by mechanisms involving increases in both cell size (hypertrophy) and cell number (hyperplasia). Pancreatic growth was stimulated by distal (but not proximal) SBR; NT did not augment this response. The authors conclude that NT augments intestinal growth after SBR by mechanisms involving an increase in overall mucosal cellularity. Administration of NT may be therapeutically useful to enhance mucosal regeneration during the early period of adaptive hyperplasia after SBR.

Effects of bolus doses of fat on small intestinal structure and on release of gastrin, cholecystokinin, peptide tyrosine-tyrosine, and enteroglucagon

To investigate the enterotrophic effects of bolus doses of long chain triglycerides, two groups of eight female Wistar rats were fed identical diets with 48.2% total calories as the essential fatty acid rich oil Efamol. To one group the oil was given in twice daily bolus doses by gavage, while for the other group the oil was mixed with the remainder of the feed and thus consumed over 24 hours. The animals were killed after 20 to 22 days. Bolus dosing significantly increased parameters of mucosal mass along the length of the small intestine in association with an increase in two hour accumulation of vincristine arrested metaphases in small intestinal crypts. In a second experiment, four replicate studies were carried out, each involving two groups of 12 rats respectively fed as described above. After 21 days one animal from each group was killed every two hours, providing regular plasma samples over 24 hours for measurement of gastrin, cholecystokinin, peptide tyrosine-tyrosine and enteroglucagon. Bolus dosing markedly enhanced release of peptide tyrosine-tyrosine and enteroglucagon, but not of gastrin or cholecystokinin. Thus, the enhanced enterotrophic effects of bolus doses of long chain triglycerides could be mediated by release of a distally located gut peptide, perhaps enteroglucagon.

Mucosal surface area of a reversed intestinal segment in rats

Only scarce knowledge exists of morphologic changes after antiperistaltic reversal of the small intestine. Previous animal models using a reversed segment of the small intestine after massive intestinal resection have been mostly concerned with assessing absorption. A rat model was therefore developed for the purpose of studying mucosal surface area in the small intestine after reversal of an intestinal segment. A reversal of 10 cm, representing a length of about 10%, was found suitable for the investigation. Marked dilatation of the reversed segment occurred. A pronounced increase in mucosal surface area caused by mucosal hyperplasia was observed. The mucosal surface area in an anastomosed, but not reversed, segment also increased markedly compared with a group undergoing no operation, although less than in the reversed segment. We conclude that a reversed intestinal segment will increase mucosal surface area in an optimal length used for this purpose. This increase is possibly caused by prolonged exposure to intestinal chyme.

Inhibitory effect of a cholecystokinin antagonist on the proliferative response of the pancreas to pancreatobiliary diversion

Since pancreatobiliary diversion probably stimulates pancreatic growth by increasing cholecystokinin secretion, the effect of the cholecystokinin antagonist CR-1409 on this adaptive response was tested. Male Wistar rats (n = 108) weighing 220-250g were randomised to receive either pancreatobiliary diversion (n = 60) or sham diversion (n = 48) and thereafter to receive either saline injections or CR-1409 (10 mg/kg/day, subcutaneously). Rats were killed at four, seven, and 14 days postoperatively, when blood was obtained for cholecystokinin assay and the pancreas was assessed for proliferative activity by three techniques: nucleic acid and protein assay, bromodeoxyuridine labelling, and metaphase arrest after vincristine administration (1 mg/kg, intraperitoneally). Pancreatobiliary diversion increased plasma cholecystokinin concentrations by 91% at seven days and 137% at 14 days, irrespective of CR-1409 treatment. Total pancreatic RNA content was doubled by pancreatobiliary diversion at four days (2.15 v 1.07 mg/100 g body weight: p less than 0.001) and at seven days (3.43 v 1.76 mg/100 g: p less than 0.001), and trebled at 14 days (4.27 v 1.32 mg/100 g: p less than 0.001). Pancreatobiliary diversion increased bromodeoxyuridine labelling index from 1.1 to 3.7% at seven days and the cell birth rate from 0.09 to 0.06%. CR-1409 completely abolished this proliferative response and partly prevented the rise in RNA. The results confirm pancreatic hypertrophy and increased acinar cell proliferation after pancreatobiliary diversion. CR-1409 prevents this adaptive growth, probably by blocking cholecystokinin receptors. Bromodeoxyuridine labelling and the metaphase arrest technique may be used to assess pancreatic cell kinetics.

Short-bowel syndrome: a review of the role of nutrition support

Advances in long-term venous access devices and in parenteral nutrition solutions have made it possible for patients with severe short bowel syndrome to survive and to live in our society. The spectrum of this disease is such that some patients may be able to lessen their dependence or even become free from parenteral therapy. This review will discuss the role of nutrition support in the patient with short bowel syndrome.

Effect of defunction on cytokinetics and cancer at colonic suture lines

An intestinal suture line potentiates experimental carcinogenesis in its vicinity, probably due to adaptive hyperplasia. By contrast, a defunctioning colostomy causes distal hypoplasia, and fewer tumours develop. Male Sprague-Dawley rats (n = 160) were used to study adaptation (assessed by a stathmokinetic technique) and carcinogenesis (induced by azoxymethane) at an end-to-end anastomosis that was raised in either functioning or defunctioned left colon. Controls had no procedure and other rats had proximal colostomy alone. Defunction had a profound antitropic effect on the colon, reducing bowel length and weight and crypt cell production rate (CCPR) by 22-56 per cent. Anastomotic CCPR was increased by a factor of 2.6 over controls: mean(s.e.m.) values of 12.71(2.85) versus 4.87(0.41) cells/crypt/h (P less than 0.01), but defunction reduced this by 76 per cent to a mean(s.e.m.) value of 3.00(0.52) cells/crypt/h below that in the intact colon. In the left colon, 39-50 per cent of tumours were sited at the anastomosis. Compared with controls there were 77 per cent fewer tumours in defunctioned colon, but they still favoured the site of anastomosis. Neoplasms at the colostomy site accounted for 74-77 per cent of all right-sided tumours. Anastomosis and defunction have powerful but contrasting effects on colonic adaptation and carcinogenesis; when combined they tend to cancel each other out.