Intestinal function and metabolism in the early adaptive phase after massive small bowel resection in the rat.

PURPOSE: The aim of this study was to investigate the early adaptive responses in metabolism and gut function after massive small bowel resection. METHODS: Male Wistar rats underwent an 80% small bowel resection (Ent group, n = 9) or a transection and reanastomozing (Sham group, n = 7). After 24 hours, substrate fluxes across the gut were determined together with intestinal protein synthesis, polyamine concentrations in gut tissue, and gut function by testing intestinal permeability using the urinary recovery of lactulose and rhamnose. To test for the effect of starvation, healthy starved rats were studied. RESULTS: In the Ent group, intestinal uptake of glucose, lactate, glutamine, phenylalanine, branched chain amino acids, and total amino acids were equal to or higher than that in Sham rats. Intestinal protein synthesis increased, accompanied by an increase in spermidine to spermine polyamine ratios in the ileum and in the jejunal muscular layer. The urinary lactulose to rhamnose ratio also increased, suggesting increased intestinal permeability. CONCLUSIONS: 24 hours after massive small bowel resection, adaptive responses in metabolism and gut function already can be observed, as indicated by increased intestinal uptake of substrates and increased protein synthesis. This, however, is accompanied by an increase in intestinal permeability, which may indicate impaired intestinal barrier function. J Pediatr Surg 36:1746-1751.

Enteral inulin does not affect epithelial gene expression and cell turnover within the ileoanal pouch.

PURPOSE: This study evaluates the effects of enteral inulin on ileoanal pouch functioning by studying epithelial gene expression, cell turnover, and mucosal morphology. METHODS: Twenty patients with an ileoanal pouch received 24 g of inulin daily for three weeks, then a four-week wash-out period, and a placebo for three weeks. In this randomized, double-blind, crossover study, biopsy specimens of pouch mucosa were taken after each test period. Mucosal morphology, inflammation, epithelial proliferation, and cell death were assessed histologically. Expressions of proapoptotic and antiapoptotic regulators, intestinal fatty acid-binding protein, and mucin were quantified by Western blotting or enzyme-linked immunosorbent assay. The number of intestinal fatty acid-binding protein expressing cells was histologically assessed and a high iron diamine/Alcian blue staining was performed to discriminate between sulfated and nonsulfated acidic mucins. RESULTS: Inulin supplementation neither altered mucosal morphology nor influenced inflammation, epithelial cell proliferation, or cell death. The ratio between the proapoptotic and antiapoptotic regulators did not change after inulin supplementation. The number of intestinal fatty acid-binding protein-producing enterocytes and the intestinal fatty acid-binding protein expression level increased after inulin treatment, but did not reach statistical significance. The intestinal fatty acidbinding protein expression level correlated with the Pouchitis Disease Activity Index, which was at the brink of significance (P = 0.06). Mucin expression and the ratio between sulfated and nonsulfated acidic mucins were not altered by inulin supplementation. CONCLUSION: In this prospective study, inulin supplementation did not significantly alter pouch mucosal functioning because neither epithelial homeostasis nor epithelial gene expression was significantly altered by enteral inulin.

The role of apoptosis during intestinal adaptation after small bowel resection.

BACKGROUND/PURPOSE: Adaptation after small bowel resection (SBR) is characterised by a new set point in the balance of enterocyte proliferation and apoptosis. Apoptosis is gene directed. The authors hypothesised that the adaptive response is influenced positively by antiapoptotic gene products (eg, bcl-2 gene-produced protein). The authors tested this hypothesis by studying the effect of bcl-2 overexpression on intestinal adaptation after SBR. METHODS: Male bcl-2 transgenic mice, overexpressing bcl-2 in the small intestinal epithelium, and wild type control mice underwent either a 75% mid-SBR, or a sham operation. The 4 experimental groups consisted of resection wild type (n = 8), transection wild type (n = 6), resection bcl-2 transgenic (n = 8), and transection bcl-2 transgenic (n = 8). Seven days postoperatively small bowel was harvested; total weight, mucosal weight, and mucosal protein, DNA, and RNA content in jejunal and ileal tissue were determined to quantitate the hyperplastic response. RESULTS: Compared with sham-operated animals, SBR resulted in increased total jejunal weight; mucosal weight; and mucosal protein, DNA, and RNA content. Furthermore, in the SBR groups, the jejunal mucosal weight and mucosal protein and DNA content were significantly higher in the bcl-2 transgenic mice compared with the wild-type mice. No differences were observed between any of these parameters in the transection wild-type and transgenic mice. In the ileum, similar changes were observed. The differences between resected and transected wild-type mice were less pronounced, and only total ileal weight and mucosal protein content reached statistical significance. In the transgenic animals, all ileal variables, with the exception of mucosal RNA content, were significantly higher in the SBR group than in the transected group. SBR in the transgenic mice resulted in higher ileal mucosal weight and mucosal protein, DNA, and RNA content compared with the wild-type mice. CONCLUSIONS: The results show that the murine SBR model is a true representation of the process of adaptation after SBR. Furthermore, major components of the adaptive response, both in the jejunum and in the ileum, are significantly more pronounced in the bcl-2 transgenic mice than in the wild-type control animals. Thus, it can be concluded that intestinal hyperplasia after SBR is significantly enhanced by overexpression of the anti-apoptotic bcl-2 gene product. This finding should prompt further research on the effects of antiapoptotic interventions on adaptation after SBR.

Enhanced renal vein ammonia efflux after a protein meal in the pig.

BACKGROUND/AIMS: The intake of dietary protein has been associated with increased arterial ammonia levels. However, the origin of this rise in ammonia levels is unknown. This study was designed to examine whether this increase is caused by ammonia formed by the gut escaping hepatic clearance, or ammonia formed by the kidney and subsequently released into the circulation. METHODS: Splanchnic and renal fluxes of ammonia and amino acids were studied in 10 pigs that were fed in a randomized cross-over design with a protein meal (n = 8), a meal with an equimolar amount of free amino acids (n = 8) or an iso-osmolar NaCl solution (n = 6). RESULTS: After the protein meal, and less pronounced after the amino acid meal, arterial ammonia levels increased from approximately 25 to 75 micromol/l. Arterial pH changes and splanchnic ammonia release were negligible. The renal vein ammonia efflux increased after the protein meal (0.67+/-0.10 to 1.94+/-0.35 micromol/kg bw/min) and to a lesser degree after the amino acid meal (to 1.20+/-0.39 micromol/kg bw/ min). Renal uptake of alanine, and not glutamine, increased stoichiometrically, paralleling the enhanced renal vein ammonia efflux. CONCLUSIONS: Arterial ammonia increases after a meal in pigs, coinciding with a negligible splanchnic ammonia release, but increased renal vein ammonia efflux. Thus, post-prandial plasma ammonia levels appear to be mainly related to renal ammoniagenesis. Alanine appears to be the main precursor for this renal ammoniagenesis in the pig.

Effects of parenteral arginine supplementation on the intestinal adaptive response after massive small bowel resection in the rat.

BACKGROUND: Arginine (ARG) and its metabolic products (polyamines and nitric oxide) are known to affect gut function and protein synthesis in various tissues. The aim was to study the effect of parenteral ARG supplementation on intestinal adaptation and intestinal function in rats after massive small bowel resection (SBR). METHODS: Fasted rats (275 g) were studied 24 h after 80% SBR. At t = 6 h, t = 12 h, and t = 18 h after SBR, a 300 mM ARG solution (ARG, n = 9), 5 ml/100 g body weight, was given subcutaneously. Controls received iso-osmolaric amounts of NaCl (NaCl, n = 9) or alanine (ALA, n = 8). Twenty-four hours after operation substrate fluxes across the gut were determined together with intestinal protein synthesis, polyamine concentrations in gut tissue, and gut function by testing intestinal permeability using the urinary recovery of lactulose and rhamnose. RESULTS: Intestinal fluxes did not differ among groups, except for an increased production of ornithine and a decreased uptake of glutamine after ARG supplementation. Also, intracellular arginine and ornithine concentrations were higher in the jejunum, accompanied by lower concentrations of other amino acids. Intracellular putrescine and gamma-aminobutyric acid, a breakdown product of putrescine, were higher. However, spermidine and spermine were not. Protein synthesis was lower in the ARG group, while intestinal permeability decreased. CONCLUSIONS: Parenteral arginine supplementation in rats with massive SBR leads to a slowing of intestinal adaptation, indicated by reduced glutamine uptake and protein synthesis. The exact mechanism of this inhibitory effect remains to be elucidated. Intestinal permeability, however, benefits from arginine supplementation, possibly related to better enterocyte differentiation.

Renal arginine metabolism in fasted rats with subacute short bowel syndrome.

1. Arginine can be produced in the kidney from citrulline. An important source of circulating citrulline is the intestinal breakdown of glutamine. Consequently, partial enterectomy leads to decreased plasma citrulline levels. The aim of the present study was to investigate the effect of diminished arterial citrulline levels on renal arginine production and total-body free arginine pools.2. Renal amino acid metabolism was studied 24 h after 75% small bowel resection in rats fasted overnight (16 h) (n=12; total fast 40 h). Sham-operated (n=9) and non-operated 16-h and 40-h fasted controls were studied in parallel (n=8/n=7). During anaesthesia, L-(2, 3-3H)-arginine and para-aminohippuric acid were infused until steady state. Subsequently, arterial and renal venous blood samples were taken. Concentrations of para-aminohippurate and amino acids and specific activity of arginine and citrulline were measured to calculate renal plasma flow, net renal uptake or release, and unidirectional influx or efflux of arginine and citrulline, as well as whole-body arginine turnover.3. Arterial citrulline was decreased in enterectomized rats compared with sham-operated rats (23+/-3 versus 44+/-6 microM). Net renal citrulline uptake and arginine release were almost stoichiometric (-36+/-7 and 38+/-6 nmol.min-1. 100 g-1 body weight respectively in sham-operated rats) and were both diminished by 50% in enterectomized versus sham-operated rats. In all groups, net renal arginine production accounted for less than 10% of whole-body rate of arginine appearance (488 nmol.min-1.100 g-1 body weight in the sham group). Despite decreased net renal citrulline consumption and renal arginine production in enterectomized rats, whole-body rate of arginine appearance and arterial arginine did not change significantly.4. In conclusion, net renal arginine production is reduced 24 h after 75% enterectomy in fasted rats. However, this does not have important effects on whole-body arginine production.

Intragastric bolus feeding of meals containing elementary, partially hydrolyzed or intact protein causes comparable changes in interorgan substrate flux in the pig.

Dietary protein given as pre-digested protein improves the nutritional value of the meal. However, studies measuring absorption kinetics of pre-digested protein or free amino acid mixtures are scarce and suffer from methodological problems. Therefore, the study was designed to study whether differences in absorption kinetics play a role. The kinetics of substrate production or consumption after a rapid gastrically-infused meal was studied across the portal drained viscera, liver and hindquarter in conscious, multicatheterized healthy pigs of 20-22 kg (n = 12). The meal contained carbohydrates and protein (1.44 g/kg body weight) as intact whey protein isolate, moderately-hydrolyzed protein digest or equivalent amino acid mixture (including glutamine and asparagine). For almost all amino acids and glucose, intestinal production, liver and hindquarter uptake were similar. The higher liver urea production (less than 15% of total alpha-amino intake) after the meals with pre-digested protein or free amino acids was related to the marginally higher intestinal glutamine breakdown (not significant) and ammonia production. Our results suggest that in the normal healthy pig, uptake and metabolism of moderately hydrolyzed,free amino acid or intact protein meals with identical composition is not different.

Supplementation of enteral nutrition with butyrate leads to increased portal efflux of amino acids in growing pigs with short bowel syndrome.

Previously, short-chain fatty acids (SCFAs) infused into the hindgut or administered intravenously have been shown to stimulate intestinal adaptation after massive small bowel resection. To study the effects of enterally supplemented n-butyrate on food digestion and absorption in growing pigs with short bowel syndrome, the authors examined the portal efflux of glucose and amino acids during a meal. In 12 growing pigs, 75% of the small intestine was resected. Five control (CONT) animals underwent transection and reanastomosis of the small bowel. A splenic vein, the aorta, the portal vein, and the stomach were catheterized. Postoperatively, seven enterectomized (ENT) pigs and the CONT pigs were fed by infusion of a liquid diet, without SCFAs, through the gastrostomy catheter. Five enterectomized animals received the same diet, supplemented with butyrate (ENTB) (0.26 g/kg body weight/d). After 3 weeks, the portal efflux of amino acids and glucose was measured after 2 hours of constant feeding. The portal efflux of glucose expressed per kilogram of body weight in the ENT group was 10% of that in the CONT group, and in the ENTB group it was 42%. No significant difference in portal glucose efflux between the ENT and the ENTB groups was found. The portal efflux of amino acids during a meal in the ENT group in relation to the CONT groups was 34%; in the ENTB group it was 63%. These data suggest that enteral supplementation with SCFAs leads to improvement of intestinal food digestion and absorption during short bowel syndrome, possibly related to improved intestinal adaptation.