Nutrition, operations, and intestinal adaptation

Glucose transporters in the small intestine in health and disease

Absorption of monosaccharides is mainly mediated by Na+-D-glucose cotransporter SGLT1 and the facititative transporters GLUT2 and GLUT5. SGLT1 and GLUT2 are relevant for absorption of D-glucose and D-galactose while GLUT5 is relevant for D-fructose absorption. SGLT1 and GLUT5 are constantly localized in the brush border membrane (BBM) of enterocytes, whereas GLUT2 is localized in the basolateral membrane (BLM) or the BBM plus BLM at low and high luminal D-glucose concentrations, respectively. At high luminal D-glucose, the abundance SGLT1 in the BBM is increased. Hence, D-glucose absorption at low luminal glucose is mediated via SGLT1 in the BBM and GLUT2 in the BLM whereas high-capacity D-glucose absorption at high luminal glucose is mediated by SGLT1 plus GLUT2 in the BBM and GLUT2 in the BLM. The review describes functions and regulations of SGLT1, GLUT2, and GLUT5 in the small intestine including diurnal variations and carbohydrate-dependent regulations. Also, the roles of SGLT1 and GLUT2 for secretion of enterohormones are discussed. Furthermore, diseases are described that are caused by malfunctions of small intestinal monosaccharide transporters, such as glucose-galactose malabsorption, Fanconi syndrome, and fructose intolerance. Moreover, it is reported how diabetes, small intestinal inflammation, parental nutrition, bariatric surgery, and metformin treatment affect expression of monosaccharide transporters in the small intestine. Finally, food components that decrease D-glucose absorption and drugs in development that inhibit or downregulate SGLT1 in the small intestine are compiled. Models for regulations and combined functions of glucose transporters, and for interplay between D-fructose transport and metabolism, are discussed.

Somatostatin and Its Analogs in the Short Bowel Syndrome

The use of somatostatin to manage diarrhea associated with the short gut syndrome is impractical because of its need to be given by continuous infusion and a rebound effect on stool output with cessation of therapy. Octreotide has been used more successfully to control stool and electrolyte losses in patients with shortened gastrointestinal tracts. In published series and studies, all subjects appear to decrease stool losses, but clinical benefit for long-term use is not achieved for all patients. In the patients who do respond, the need for parenteral nutrition and intravenous hydration has been decreased or eliminated. The optimal dose is unclear, but many patients respond to 50-micrograms injections twice daily. Several investigations noted no additional beneficial effects with escalating dosages. Adverse effects include impairment of fat absorption, which may offset the therapeutic benefits of octreotide. The patients with the greatest response appear to have the least fat malabsorption. Other adverse effects noted when using octreotide for control of the short gut syndrome include pain associated with subcutaneous injection and abdominal complaints. Other potential concerns include the effect on gallstone formation in this high-risk population and intestinal adaptation.

Dietary sulfur amino acid supplementation reduces small bowel thiol/disulfide redox state and stimulates ileal mucosal growth after massive small bowel resection in rats

Following massive small bowel resection in animal models, the remnant intestine undergoes a dynamic growth response termed intestinal adaptation. Cell growth and proliferation are intimately linked to cellular and extracellular thiol/disulfide redox states, as determined by glutathione (GSH) and GSH disulfide (GSSG) (the major cellular redox system in tissues), and cysteine (Cys) and its disulfide cystine (CySS) (the major redox system in plasma), respectively. The study was designed to determine whether dietary supplementation with sulfur amino acids (SAA) leads to a greater reduction in thiol/disulfide redox state in plasma and small bowel and colonic mucosa and alters gut mucosal growth in an established rat model of short bowel syndrome (SBS). Adult rats underwent 80% jejunal-ileal resection (RX) or small bowel transection (surgical control) and were pair-fed either isonitrogenous, isocaloric SAA-adequate (control) or SAA-supplemented diets (218% increase vs. control diet). Plasma and gut mucosal samples were obtained after 7 d and analyzed for Cys, CySS, GSH, and GSSG concentrations by HPLC. Redox status (E(h)) of the Cys/CySS and GSH/GSSG couples were calculated using the Nernst equation. SAA supplementation led to a greater reduction in E(h) GSH/GSSG in jejunal and ileal mucosa of resected rats compared with controls. Resected SAA-supplemented rats showed increased ileal adaptation (increased full-thickness wet weight, DNA, and protein content compared with RX control-fed rats; increased mucosal crypt depth and villus height compared with all other study groups). These data suggest that SAA supplementation has a trophic effect on ileal adaptation after massive small bowel resection in rats. This finding may have translational relevance as a therapeutic strategy in human SBS.

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.

New growth factor therapies aimed at improving intestinal adaptation in short bowel syndrome

Short bowel syndrome (SBS) is used to describe a condition of malabsorption and malnutrition resulting from the loss of absorptive area following massive small bowel resection. The key to improved clinical outcome after massive small bowel resection is the ability of the residual bowel to adapt. Although still in experimental stages, a major goal in the management of SBS may be the augmented use of growth factors to promote increased adaptation. A number of growth factors have been implicated in promoting the adaptation process. The best-described growth factors are reviewed: glucagon-like peptide-2 (GLP-2), epidermal growth factor (EGF), and growth hormone (GH). This article reviews the ability of recombinant GLP-2, EGF and GH to modulate structural and functional aspects of intestinal adaptation following small bowel resection. Although these growth factors have shown promise, small sample size, inconsistent measurement parameters and uncontrolled study designs have hampered the acquisition of strong data advocating the use of growth factor treatment for SBS. Multicenter trials using well-defined outcome measures to assess clinical efficacy are needed to direct the clinical indications, timing and duration of therapy and assess potential risks associated with growth factor therapies.

Recommended and actual calorie intake of intensive care unit patients in a private tertiary care hospital in the Philippines

OBJECTIVES

This study compared the computed nutrient requirements of geriatric patients under critical care with their actual intake within the first 3 d after admission to the intensive care unit (ICU) and determined the percentage of patients who achieved adequate intake.

METHODS

Fifty-eight geriatric patients who were admitted to the ICU from September to December 2002 were prospectively enrolled. Recommended and actual calorie intakes per patient were recorded and mean amount of carbohydrate, protein, and fat consumed were calculated. Student's t test was used to compare actual with recommended nutrient intakes.

RESULTS

Actual in relation to recommended nutrient intake was inadequate (41.5% on day 1 to 71.7% on day 3 for calories and 21.1% on day 1 to 24.3% on day 3 for protein, P < 0.001). Carbohydrate intake was low (falling from 61.9% on day 1 to 39.8% on day 3, P < 0.001) and fat intake was also low (increasing from 29.4% to 37.9% on day 3, P < 0.001). The percentage of patients who achieved adequate intake was 51.2% on day 1 and increased to 73.2% on day 3.

CONCLUSIONS

The intake of geriatric patients in the ICU is low, with differences in actual and recommended intakes. Delivering what is recommended is still a goal to be realized in the ICU setting.

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.

Teduglutide ([Gly2]GLP-2) protects small intestinal stem cells from radiation damage

Glucagon-like peptide-2 and its dipeptidyl peptidase (DP-IV) resistant analogue teduglutide are trophic for the gastrointestinal epithelium. Exposure increases villus height and crypt size and results in increased overall intestinal weight. As these effects may be mediated through stimulation of the stem cell compartment, they may promote intestinal healing and act as potential anti-mucositis agents in patients undergoing cancer chemotherapy. A study was initiated to investigate the protective effects of teduglutide on the murine small intestinal epithelium following gamma-irradiation using the crypt microcolony assay as a measure of stem cell survival and functional competence. Teduglutide demonstrated intestinotrophic effects in both CD1 and BDF1 mouse strains. In BDF1 mice, subcutaneous injection of GLP-2 or teduglutide (0.2 mg/kg/day, b.i.d.) for 14 days increased intestinal weight by 28% and resulted in comparable increases in crypt size, villus height and area. Teduglutide given daily for 6 or 14 days prior to whole body, gamma-irradiation significantly increased crypt stem cell survival when compared with vehicle-treated controls. The mean levels of protection over a range of doses provided protection factors from 1.3 to 1.5. A protective effect was only observed when teduglutide was given before irradiation. These results suggest that teduglutide has the ability to modulate clonogenic stem cell survival in the small intestine and this may have a useful clinical application in the prevention of cancer therapy-induced mucositis.

Alpha-ketoglutarate-supplemented enteral nutrition: effects on postoperative nitrogen balance and muscle catabolism

Enteral feeding in the early postoperative phase may improve gut integrity and reduce infectious complications after trauma and surgery. The aim of the current study was to evaluate the feasibility of alpha-ketoglutarate enrichment of enteral feeding and the effect on protein metabolism after major surgery. Patients undergoing elective abdominal surgery were randomly allocated to receive a standard whole-protein-based enteral nutrition solution (n = 9) or an isonitrogenous, isocaloric solution enriched with alpha-ketoglutarate (n = 11) for 5 d postoperatively. The nutritional goals by day 4 were 25 kcal and 0.17 g of nitrogen, respectively, per kilogram of body weight every 24 h. Standard blood analysis, including prealbumin and C-peptide, was performed preoperatively and on days 1, 3, and 6. Urine was collected daily for nitrogen and 3-methylhistidine analyses. Due to restricted tolerance to enteral feeding, the nitrogen delivery reached only 0.10 g of nitrogen per kilogram of body weight. Transthyretin decreased by 25% in both groups, and albumin decreased significantly in the enriched group compared with the standard nutrition. There were no significant differences in nitrogen balance, excretion of 3-methylhistidine, or clinical outcome between groups. Enrichment of a whole-protein-based formula with alpha-ketoglutarate did not improve protein metabolism or decrease muscle catabolism after major abdominal surgery.

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.

Analysis of mucosal regeneration and the expression profile of heat shock protein 70 in the isolated small bowel segment

To investigate the mechanisms underlying the regeneration of the denervated small bowel segment from ischemic injury, we examined the heat shock protein 70 (HSP70) expression profile and compared it to the histopathological and proliferative changes seen in an isolated bowel segment using a rabbit model. Two weeks following the small bowel segment transplantation to the subcutaneous space, the vascular pedicle was sectioned. Next, the rabbits were divided into three groups based on the collection time of the isolated bowel segment (3, 7, and 14 days for Groups A, B, and C, respectively). The unsectioned small bowel segment was utilized as a control for each group. Histological studies showed that no experimental group recovered from mucosal injury. The bromodeoxyuridine labeling index showed that the more severe mucosal injury group had the highest bromodeoxyuridine incorporation. In the experimental groups, HSP70 immunoreactivity was intensely seen in the regenerating epithelial cells and inflammatory cells. In the control mucosa, HSP70 immunoreactivity was weakly seen in the subepithelial stromal tissue, crypt cells and not in epithelial cells. The present study shows that the isolated bowel segment requires longer periods for regeneration from ischemic injury and HSP70 may play an important role during the regeneration process.

Luminal and systemic signals trigger intestinal adaptation in the juvenile python

Juvenile pythons undergo large rapid upregulation of intestinal mass and intestinal transporter activities upon feeding. Because it is also easy to do surgery on pythons and to maintain them in the laboratory, we used a python model to examine signals and agents for intestinal adaptation. We surgically isolated the middle third of the small intestine from enteric continuity, leaving its mesenteric nerve and vascular supply intact. Intestinal continuity was restored by an end-to-end anastomosis between the proximal and distal thirds. Within 24 h of the snake's feeding, the reanastomosed proximal and distal segments (receiving luminal nutrients) had upregulated amino acid and glucose uptakes by up to 15-fold, had doubled intestinal mass, and thereby soon achieved total nutrient uptake capacities equal to those of the normal fed full-length intestine. At this time, however, the isolated middle segment, receiving no luminal nutrients, experienced no changes from the fasted state in either nutrient uptakes or in morphology. By 3 days postfeeding, the isolated middle segment had upregulated nutrient uptakes to the same levels as the reanastomosed proximal and distal segments, but it still lacked any appreciable morphological response. These contrasting results for the reanastomosed intestine and for the isolated middle segment suggest that luminal nutrients and/or pancreatic biliary secretions are the agents triggering rapid upregulation of transporters and of intestinal mass and that systemic nerve or hormonal signals later trigger transporter regulation but no trophic response.

Management of the patient with short bowel syndrome

Extensive resection of the small bowel results in impaired digestion of macronutrients and malabsorption of nutrients, fluid, electrolytes, and minerals. Gastric acid hypersecretion and alterations in gut hormonal response further contribute to the problem. Diarrhea, dehydration, electrolyte and acid/base abnormalities, and macronutrient and micronutrient deficiencies ensue, and is termed the short bowel syndrome (SBS). Rare disorders, such as essential fatty acid deficiency and D-lactic acidosis, are a greater concern for the SBS patient. These patients' lives are significantly impacted, and they require close monitoring by a medical team knowledgeable about the disease and its nutritional, metabolic, and psychosocial consequences. Immediate therapies are directed toward fluid resuscitation, wound healing, and initiation of early nutrition support. After medical stabilization, multiple nutritional and medicinal therapies are used to aid bowel adaptation and prevent medical crisis. Advanced practice nurses should be knowledgeable about SBS to educate patients and families about this disease, associated therapies and changes in lifestyle, and how to detect and manage acute changes in medical condition.

Ontogeny of intestinal nutrient transport

Children born prematurely lack the ability to digest and to absorb nutrients at rates compatible with their nutritional needs. As a result, total parenteral nutrition may need to be given. While this nutritional support may be life-saving, the baby who receives this therapy is exposed to the risks of possible sepsis, catheter dysfunction, and liver disease. The rodent model of postnatal development provides a useful framework to investigate some of the cellular features of human intestinal development. The up-regulation of intestinal gene expression and precocious development of intestinal nutrient absorption can be achieved by providing growth factor(s) or by modifying the composition of the maternal diet during pregnancy and nursing or the weaning diet of the infant. Accelerating the digestive and absorptive functions of the intestine would thereby allow for the maintenance of infant nutrition through oral food intake, and might possibly eliminate the need for, and risks of, total parenteral nutrition. Accordingly, this review was undertaken to focus on the adaptive processes available to the intestine, to identify what might be the signals for and mechanisms of the modified nutrient absorption, and to speculate on approaches that need to be studied as means to possibly accelerate the adaptive processes in ways which would be beneficial to the newborn young.Key words: absorption, adaptation, diet, peptides.

Differential jejunal and colonic adaptation due to resection and IGF-I in parenterally fed rats

Patients with severe short-bowel syndrome (SBS) often require long-term total parenteral nutrition (TPN) to maintain their nutritional status because of limited intestinal adaptation. Growth factors, including insulin-like growth factor I (IGF-I), are under investigation to promote intestinal adaptation and tolerance to oral feeding. We investigated structural and functional adaptation of the jejunum and colon in four groups of rats maintained with TPN for 7 days after a 60% jejunoileal resection and cecectomy or sham surgery and treatment with IGF-I or vehicle. Resection alone did not stimulate jejunal growth. IGF-I significantly increased jejunal mucosal mass, enterocyte proliferation, and migration rates. IGF-I decreased jejunal sucrase specific activity and reduced active ion transport and ionic permeability; resection alone had no effect. In contrast, resection significantly increased colonic mass and crypt depth but had no effect on active ion transport or ionic permeability. IGF-I had minimal effects on colonic structure. IGF-I but not resection stimulates jejunal adaptation, whereas resection but not IGF-I stimulates colonic growth in rats subjected to a model for human SBS. IGF-I treatment may improve intestinal adaptation in humans with SBS.

Effects of oral Saccharomyces boulardii on bacterial overgrowth, translocation, and intestinal adaptation after small-bowel resection in rats

BACKGROUND

Small-bowel resection in animals results in alterations of the morphology and functional adaptation in the remaining intestine. The aim of our study was to study the effect of Saccharomyces boulardii versus placebo in rats after 50% small-bowel resection.

METHODS

Sixty-three rats were assigned to one of three groups: small-bowel resection (n = 31), transected surgery controls (n = 16), or non-surgical controls (n = 16). Of the 31 rats with small-bowel resection, 15 were given S. boulardii (140 mg/dl), and 16 were given placebo. Intestinal markers measured included bacterial overgrowth (BO) on days 4 and 8 and translocation into mesenteric lymph nodes, liver, and spleen. Markers of small-bowel adaptation included histomorphology of the mucosa, protein content, and various brush-border enzymes (sucrase, glucoamylase, n-aminopeptidase).

RESULTS

In the jejunal mucosal samples on day 8, S. boulardii-treated rats showed a significant increase in protein content (58.3 +/- 12 mg/10 cm) compared with placebo-treated rats (29.2 +/- 1.8) or non-surgery controls (18.3 +/- 1.2; P < 0.001). S. boulardii-treated rats also had significantly higher levels of all three brush-border enzymes. A significant increase of enzyme-specific activities was observed in the ileum of S. boulardii resected rats compared with the placebo resected group on day 4, and no significant differences were seen in the remnant ileum except an increase in protein content in S. boulardii-treated rats on day 8. Histomorphometric studies showed no differences in ileal villus height or translocation frequencies by day 8 in S. boulardii or placebo resected rats.

CONCLUSIONS

These data indicate that, after resection, S. boulardii does not modify bacterial overgrowth or translocation frequency but does significantly enhance the functional adaptation of the remaining intestinal segments.

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.

An increase in mucosal insulin-like growth factor II content in postresectional rat intestine suggests autocrine or paracrine growth stimulation

BACKGROUND

Luminal nutrients and growth factors regulate postresectional intestinal growth. The interplay between glutamine and regulatory gastrointestinal peptides is not known.

METHODS

The effects of intestinal resection on tissue and plasma concentrations of peptides were studied in 60 Sprague-Dawley rats divided into resected, transected, or unoperated groups. Subgroups were fed either a glutamine-free or a glutamine-supplemented diet for 7 days. Epidermal growth factor, transforming growth factor-alpha, insulin-like growth factors (IGF) I and II, peptide YY (PYY), and enteroglucagon were analyzed in intestinal mucosa and in portal plasma by radioimmunoassay.

RESULTS

No glutamine-specific effects were seen. The mucosal content of IGF-II (P < 0.01) and the portal levels of enteroglucagon and PYY (P < 0.05-0.01) increased after intestinal resection.

CONCLUSIONS

The increase in PYY and enteroglucagon in portal blood supports a hormonal role in the postresectional adaptation. The increase in IGF II in the ileal mucosa, without changes in plasma, implies autocrine or paracrine growth stimulation at this stage after resection.

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.

Long-term metabolic and nutritional effects of urinary diversion

OBJECTIVES

To evaluate the long-term metabolic and nutritional consequences of interposing intestinal segments in the urinary tract.

METHODS

Comprehensive analyses of blood and urine were performed in 20 patients with conduit urinary diversion and in 19 with continent cecal reservoir for urine, all with normal or near-normal renal function. The mean follow-up time was 15 years in the conduit group and 9 years in the reservoir group.

RESULTS

In both patient groups, arterial blood gas analysis revealed a tendency to metabolic acidosis with respiratory compensation. Although no hyperchloremia was found in either group, the mean value of serum chloride was significantly higher (P < 0.05) in the reservoir group than in the conduit group. The calciotropic factors, plasma lipids, lipoproteins, and liver function values were normal in both groups. Serum vitamin B12 levels were subnormal in 3 conduit and 2 reservoir patients, but other studied variables of intestinal absorption were within normal limits. Conduits utilizing colonic segments showed calcium excretion on the same level as in reservoirs, which was significantly higher than in conduits made from ileal segments.

CONCLUSIONS

Except for increased risk of vitamin B12 deficiency, no major adverse metabolic or nutritional effects of conduit or continent urinary diversion were found at long-term observation in patients with well-preserved renal function. Lifelong surveillance of vitamin B12 levels is necessary in these patients.

Short chain fatty acids relax isolated resistance arteries from the human ileum by a mechanism dependent on anion-exchange

Ileal resistance arteries (internal diameter 184-337 microns) were discussed out under microscope and mounted in a microvascular myograph for isometric tension recording. Experiments were designed to test compounds trophic to the small intestine, namely, epidermal growth factor, glutamine and the three short chain fatty acids, acetic, propionic and butyric acid, for effects on vascular tone. Glutamine in concentrations up to 30 mM and epidermal growth factor in concentrations up to 1 microM had no contractile or relaxant effects on the resistance arteries. The three short chain fatty acids alone and in combination, however, caused a concentration-dependent (range 0.1-30 mM) relaxation of resistance arteries precontracted with 50 mM KCl. This relaxant effect was significantly inhibited by the presence of the anion-exchange inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid whereas it was unaffected by removal of the endothelium, presence of indomethacin, propranolol or phentolamine. These data suggest that the trophic effects of glutamine and epidermal growth factor on the small intestinal mucosa cannot be explained through actions on the resistance vasculature. In contrast, the relaxant effect of short chain fatty acid on resistance arteries in vitro suggests that these compounds may be able to improve the microcirculation in vivo. An improved microcirculation will, all things considered, facilitate the growth of the small intestinal mucosa.

Morphologic and cytoproliferative patterns of duodenal mucosa in two patients after long-term total parenteral nutrition: changes with oral refeeding and relation to intestinal resection

The morphologic and cytoproliferative patterns of the duodenal mucosa of two adult patients, one of whom had a short bowel, were evaluated after more than 2 months of postoperative total parenteral nutrition and 2 and 12 months after the resumption of oral alimentation. Morphometric analysis was performed on routinely processed duodenal biopsies. Cell proliferation was evaluated by means of in vitro bromodeoxyuridine uptake. The results were compared with those obtained in five healthy controls. After parenteral nutrition, patients showed significantly lower villus height and crypt depth than those of controls and a normal bromodeoxyuridine labeling index. After 2 months of refeeding, villus and crypt returned to normal, and the labeling index was increased. After 12 months of oral refeeding, labeling index, villus height, and crypt depth were similar to those of controls. The patient with the short bowel showed a number of cells per unit length of villus and crypt significantly greater than those of the controls and of the patient who underwent shorter intestinal resection. In human duodenal mucosa, (1) hypoplasia develops after long-term total parenteral nutrition; (2) mucosal recovery occurs through an increased cell proliferation after oral refeeding; and (3) extensive small bowel resection determines the development of relative hyperplasia.

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.

Principles of nutrition therapy for short-bowel syndrome

Short-bowel syndrome is characterized by maldigestion, malabsorption, dehydration, electrolyte abnormalities, and both macronutrient and micronutrient deficiencies. Nutritional and hydration status are difficult to maintain without the provision of specialized nutrition support when more than 75% of the small intestine has been resected. Each patient's response to small-bowel resection is unique; therefore, the type of therapy must be tailored to each individual's bowel resection, complications that ensue, and specific nutrient needs. Clinical management should be guided by principles of nutrition assessment and treatment of nutrient deficiencies as well as routine monitoring of the patient's clinical course and response to therapy.

Experimental pancreatic hyperplasia and neoplasia: effects of dietary and surgical manipulation

Several studies carried out during the past two decades have investigated the effect of dietary and surgical manipulation on pancreatic growth and carcinogenesis. Diets high in trypsin inhibitor stimulate pancreatic growth and increase the formation of preneoplastic lesions and carcinomas in the rat pancreas. Cholecystokinin (CCK) is the key intermediary in this response, since both natural and synthetic trypsin inhibitors increase circulating levels of the hormone and CCK antagonists largely prevent these changes. Fatty acids enhance pancreatic carcinogenesis in both rats and hamsters, whereas protein appears to have a protective role in the rat, but to increase tumour yields in the hamster. Several surgical operations affect the pancreas. Pancreatobiliary diversion and partial gastrectomy stimulate pancreatic growth and enhance carcinogenesis, probably by means of increased CCK release. Complete duodenogastric reflux has similar effects on the pancreas but the gut peptide involved is gastrin. Although massive small bowel resection increases pancreatic growth, the marked reduction in caloric absorption probably explains its failure to enhance carcinogenesis. CCK and enteroglucagon might work in concert to modulate the tropic response of the pancreas to small bowel resection. In the pancreas, as in the large intestine, hyperplasia appears to precede and predispose to neoplasia.

Mucosal morphology in isolated bowel segments: importance of exposure to luminal contents

An isolated bowel segment (IBS) is a loop of intestine that has been freed from its mesenteric attachment after the development of vascular collaterals between the antimesenteric surface of the gut and the host organ. Surgical creation of such artificially vascularized isolated bowel segments is of interest to researchers for a variety of studies, and may be useful in the treatment of short bowel syndrome, allowing longitudinal division of the remaining small bowel to double its length. We created four surgical variants to study the ability of the collateral blood supply to maintain mucosal integrity in the presence or absence of normal luminal contents. In all groups, a collateral blood supply was created in a 5- to 7-cm segment of adult rat jejunum by hepatoenteropexy (Iowa model II). In Thiry-Vella (T-V) and isolated bowel segment (IBS) rats, this segment was exteriorized at both ends to exclude luminal contents. Control and IBS in continuity (IBS-C) loops were left in continuity. The mesentery of IBS and IBS-C rats was divided 5 weeks later, leaving the experimental segment entirely dependent on the collateral circulation. All animals were harvested at 7 weeks after the initial surgery. Tissues were analyzed for mucosal weight, protein content per centimeter of bowel, length of villi, depth of crypts, DNA content, and sucrase activity. We found that segments retaining luminal continuity had significantly higher mucosal weight and DNA content per centimeter of bowel compared with exteriorized loops.

Tropic role of enteroglucagon in pancreatic adaptation to subtotal enterectomy

Proximal small bowel resection causes pancreatic hyperplasia, presumably via a humoral mechanism. Although cholecystokinin can stimulate pancreatic growth, its proximal distribution in the gut makes it an unlikely intermediary after proximal small bowel resection. The potential roles of neurotensin and enteroglucagon were studied, since these hormones are mainly secreted from the ileum and proximal colon. Male Wistar rats (n = 50) weighing 200-250 g were randomized to receive 90 per cent proximal small bowel resection or jejunal transection and resuture (control). Rats were killed at 1 week or 1 month, when plasma was obtained for hormone assay and the pancreas was excised for protein and nucleic acid measurement. Proximal small bowel resection increased circulating enteroglucagon levels by 150 per cent at 1 week (P less than 0.002) and by 83 per cent at 1 month (P less than 0.005); neurotensin levels were unchanged. Pancreatic wet weight was 21 per cent greater 1 month after proximal small bowel resection (P less than 0.001). Proximal small bowel resection increased protein, RNA and DNA contents of the pancreas both at 1 week and at 1 month. Since plasma enteroglucagon correlated with these indices of pancreatic mass, enteroglucagon may have a pancreatotropic role (in addition to its enterotropic role).

Nutritional consequences of major gastrointestinal surgery. Patient outcome and starvation

Advances in major gastrointestinal surgery and the existence of a significant number of high-risk patients necessitate a detailed knowledge of the metabolic response to surgery and the need for adjunctive nutritional therapy. Such surgery has the potential to cause significant nutritional consequences affecting patient outcome. Often, patients present malnourished preoperatively because of their chronic gastrointestinal disease, advanced age, or comorbidity. Still others are at great risk for developing malnutrition postoperatively secondary to the hypercatabolism of prolonged illness or postoperative complications. In addition, the surgical alterations of the gastrointestinal tract might disrupt normal function sufficiently to result in chronic nutritional deficiencies. Because starvation is no longer an acceptable condition, these concerns need to be recognized prior to surgery, and if indicated, nutritional support must be initiated preoperatively. Placement of feeding jejunostomy catheters for early enteral support should be considered for all high-risk patients. Equally important, surgeons should maintain a watch for future nutritional innovations that will improve their ability to meet patients' nutritional requirements.

Nutritional support of hospitalized patients

Effective nutritional support requires sound knowledge of both basic and clinical nutrition of dogs and cats as well as familiarity with products and delivery systems. Case management includes assessment of nutritional status and estimation of fuel sources. Most starved or stressed patients use fatty acids for over 70 per cent kcalME and protein for over 20 per cent kcalME. Approximate kcal needs are calculated from maintenance energy equations. Most patients respond best to enteral nutrition. Meat-based pet foods, liquid enteral products, and nutrient modules are offered in slurries or are tube-fed. Management includes careful monitoring of patients and gradual transitions to diets with more complex nutrient sources.