Stimulation of mucosal growth by gastric and ileal infusion of single amino acids in parenterally nourished rats

Luminal nutrient signals for intestinal adaptation in pythons

Python intestine responds rapidly to luminal nutrients by increasing mass and upregulating nutrient transport. Candidates for luminal signals triggering those responses include mechanical stimulation, single or several dietary nutrients, and endogenous secretions. To identify signals, we infused into the python's small intestine either a nonnutrient solution (saline) or a single- or multinutrient solution. Python intestine failed to respond trophically or functionally to luminal infusions of saline, glucose, lipid, or bile. Infusion of amino acids and peptides, with or without glucose, induced an intermediate response. Infusion of nutritionally complete liquid formula or natural diet induced full intestinal response. Intact meals triggered full intestinal responses without pancreatic or biliary secretions, whereas direct cephalic and gastric stimulation failed to elicit any response. Hence neither physical stimulation (cephalic, gastric, or intestinal) nor the luminal presence of glucose, lipids, or bile can induce intestinal response; instead, a combination of nutrients is required (even without pancreaticobiliary secretions), the most important being amino acids and peptides. This is understandable because pythons, as carnivores, have a high-protein diet.

Enhancing bowel adaptation in short bowel syndrome

Malabsorption of both nonessential and essential nutrients, fluid, and electrolytes will, if not compensated for by increased intake, lead to diminished body stores and to subclinical and eventually clinical deficiencies. By definition, intestinal failure prevails when parenteral support is necessary to maintain nutritional equilibrium. After intestinal resection, adaptation, a progressive recovery from the malabsorptive disorder, may be seen. Research has focused on optimizing remnant intestinal function through dietary or pharmacologic interventions. In this review, factors responsible for the morphologic and functional changes in the adaptive processes are described. Results of clinical trials employing either growth hormone and glutamine or glucagon-like peptide-2 in short bowel patients are presented.

Nutritional support for Crohn's disease

This article reviews nutritional considerations that arise in the care of patients with Crohn's disease. The causes and presentation of malnutrition in these patients are discussed, and a rational method is presented for comprehensive nutritional assessment. The indications for nutritional intervention, either as supportive or primary therapy for Crohn's disease, are reviewed.

Comparative study of glycine, alanine or casein as inert nitrogen sources in endotoxemic rats

Pharmacological effects of dietary amino acids (AA) and peptides must be compared to an isonitrogenous control that is as inert as possible. To establish a rationale for the choice of such a control, potential metabolic and nutritional effects of three currently used nitrogenous controls (glycine, alanine, and casein) were evaluated in an endotoxemic rat model that has well-defined alterations in AA and protein metabolism. Five-week-old male Sprague-Dawley rats (113 +/- 1 g) were randomly assigned to four groups and received at d 0 an intraperitoneal injection of endotoxin (3 mg/kg). After withdrawal of food for 24 h, the rats were enterally refed for 48 h with a liquid diet (Osmolite((R))) supplemented with 0.19 g N. kg(-1). d(-1) in the form of glycine [lipopolysaccharide (LPS)-GLY group], alanine (LPS-ALA group) or casein (LPS-CAS group). One group (LPS group) received only Osmolite((R)). Plasma, two skeletal muscles, the liver and the intestine were then removed. Body and tissue weights and tissue protein contents did not differ among the four groups. Intestine histomorphometry showed no significant difference among groups. Jejunal hydrolase activities were significantly affected by the nitrogenous supplementations, but no effect was observed in the ileum. Only limited significant effects were observed on plasma and tissue-free AA concentrations, except for an accumulation of glycine in the plasma and tissues from the LPS-GLY group, compared to other groups. Overall, whereas glycine as a nitrogenous control should be used with care, either alanine or casein may be used as the "placebo," with the choice depending on the study to be performed.

Nutrition support in inflammatory bowel disease

The mechanisms of nutritional therapy in inflammatory bowel disease have not been thoroughly established. It is likely that a further understanding of the underlying disease process will allow better understanding of these forms of therapy, with a sounder rationale for the construction of specific diet constituents for therapy. Regardless, nutritional therapy is likely to be multidimensional, and various forms may affect different aspects of the disease process. Decreased inflammatory factors, decreased antigenic stimuli, provision of essential nutrients, improved immune function, and other factors may all be of varying importance in different patients with inflammatory bowel disease. Little work has been done on the role of diet therapy in the long-term treatment of patients with inflammatory bowel disease as a method of preventing relapse. Parenteral nutrition and elemental diets appear to have limited roles in this area. Some investigation has been done to see if minor modifications of the normal diet can prolong remission periods. Low-fiber diets are frequently recommended for patients with strictures. Whether this has any significant effect on symptoms, inflammation, or complications is unclear. Heaton et al suggested that a high-fiber, unrefined carbohydrate diet resulted in fewer and shorter hospitalizations. In a prospective follow-up study by Ritchie et al, however, these results were not able to be reproduced. Exclusion diets have also been suggested as a means of reducing relapse rates in patients with Crohn's disease. In a small, randomized, controlled trial of an exclusion diet versus an unrefined carbohydrate, fiber-rich diet, there were significantly fewer relapses among the patients treated with the exclusion diet at 6 months. These diets require intensive patient cooperation, but the potential side effects are minimal. Clearly, these findings need to be reproduced in large, prospective, randomized, controlled studies before widespread use can be advocated. A great deal of data exists on the use of nutritional supplementation in the treatment of inflammatory bowel disease, although little of it is in the form of large, randomized, controlled studies. Nutritional manipulation currently has a limited role in patients with ulcerative colitis; a much broader role exists in patients with Crohn's disease. The mechanisms by which nutritional therapy affects these diseases may include a combination of factors--decreased antigenic exposure, improved immune function, and provision of essential nutrients and calories needed for bowel regeneration.(ABSTRACT TRUNCATED AT 400 WORDS)

Alanyl glutamine-enriched total parenteral nutrition restores intestinal adaptation after either proximal or distal massive resection in rats

This study was designed to determine whether alanyl glutamine-containing total parental nutrition (TPN) can restore the impaired adaptive process of the remaining intestine, observed with administration of conventional TPN, after massive small-bowel resection. Seventy-four male Sprague-Dawley rats weighing 250 g were randomly divided into seven groups. Group I rats (n = 10) were killed after overnight fasting. Group II animals (n = 32) underwent massive small bowel resection (85%) with preservation of the first 15 cm of jejunum. Group III animals (n = 32) were also submitted to massive small-bowel resection with preservation of 15 cm of terminal ileum. Three different TPN solutions were prepared. Solution A was a conventional formulation that did not contain glutamine. Solution B contained 1.88 times the amino acid concentration of solution A. Solution C was prepared by adding alanyl glutamine (2 g/100 mL) to solution A. Solutions B and C were isonitrogenous and isocaloric. Each solution was infused to groups II and III, which were subdivided into groups IIA (n = 10), IIB (n = 11), IIC (n = 11), IIIA (n = 10), IIIB (n = 11), and IIIC (n = 11). After 1 week of TPN (270 kcal/kg per day), the experimental animals were killed and the intestine was taken for examination. Final body weight did not differ significantly among the groups, and there was no difference in nitrogen balance among the animals that received solution B or C.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotensin prevents intestinal mucosal hypoplasia in rats fed an elemental diet

Liquid elemental diets are associated with mucosal hypoplasia of both the small intestine and colon. Neurotensin, a tridecapeptide widely distributed in the gut, is trophic for the small intestine of rats fed a normal chow diet. The purpose of this study was to determine whether neurotensin could reverse the hypoplasia of intestinal mucosa that is associated with feeding a liquid elemental diet. Forty male Sprague-Dawley rats were randomized into five groups. Four groups were fed (for seven days) a glutamine-free liquid elemental diet. Subcutaneous injection of saline (control) or neurotensin (33, 100 or 300 micrograms/kg) were given to the groups of rats every 8 hr for seven days. Group five (Chow) received rat chow ad libitum for seven days. Rats were killed on day 8, and the proximal jejunum, distal ileum, and proximal colon removed. Mucosal weight, DNA, RNA, and protein contents were determined. Neurotensin (300 micrograms/kg) increased the cellularity of the small intestinal mucosa and reversed mucosal hypoplasia due to an elemental diet; a more pronounced effect was noted in the jejunum compared to the ileum. Neurotensin (33 and 100 micrograms/kg) increased mucosal DNA content in the jejunum but was not effective in reversing the hypoplasia. Neurotensin had no effect on growth of colonic mucosa. These results suggest that neurotensin may be an important trophic hormone for the small intestine. Administration of neurotensin may alleviate hypoplasia of the small bowel mucosa and maintain functional integrity of the gut during prolonged feeding of an elemental diet.

Effects of dietary whey proteins, their peptides or amino-acids on the ileal mucosa of normally fed and starved rats

The effects of three liquid diets, differing only in the molecular form of the nitrogen source (whole whey proteins, WP; trypsic whey protein hydrolysate, WPH, and amino-acid mixture, AAM) were studied on the mucosa morphology and brush border hydrolase (BBH) activities (disaccharidases, peptidases) of the ileum of normally fed male Wistar rats (controls) and during refeeding of rats starved for 72h. All three diets produced repair of the fasting induced mucosal atrophy; the AAM diet gave the most rapid response and highest villus height (p < 0.01). This was correlated with an increase in crypt mitoses (p < 0.01). Similar results were obtained in controls with AAM. The sucrase (S) and acid amino peptidase (AAP) specific activities of controls were higher (p < 0.01) on the WPH diet; neutral amino peptidase (NAP) was unaffected. Dipeptidyl peptidase IV (DDP) was lowest on AAM while glucoamylase (G) highest on WP. Fasting increased S and DDP activity, and produced no change in the other BBH. Large variations in BBH occurred during refeeding except for NAP which remained stable. Control values were restored at 96h, except for AAP. The results show that BBH and mucosa morphology of the ileum in the rat can be modified by the molecular form of the nitrogen source and that the nutritional status interferes with this adaptation. These data could have implications for the therapy of small bowel disease.

Comparison of different caloric substrates on intestinal adaptation in the rat

We compared the relative efficacy of medium- and long-chain triglycerides and dextrose on intestinal adaptation. Parenterally nourished rats received an isocaloric luminal infusion of one of these three substrates for 1 wk into either the jejunum or the ileum. Intestinal mass (mucosal weight and protein content) as well as the in vivo absorption of 5 mM glucose, valine, and aspartic acid were measured. In the jejunum, long-chain triglycerides were the most trophic, whereas in the ileum, long-chain triglycerides and dextrose were equally effective, but significantly more trophic than medium-chain triglycerides. In general, absorptive function was better maintained by dextrose and medium-chain triglycerides than long-chain triglycerides in the jejunum or by dextrose in the ileum. These data demonstrate that the jejunum and ileum respond differently to caloric substrates. Medium-chain triglycerides do not appear to have a clear superiority to long-chain triglycerides or dextrose in producing intestinal adaptation.

Stimulation of intestinal mucosal growth with intracolonic infusion of short-chain fatty acids

Dietary fiber, which stimulates intestinal mucosal growth, is fermented by anaerobic bacteria in the rat hindgut to the short-chain fatty acids (SCFA) acetate, propionate, and butyrate. Butyrate is the preferred oxidative fuel of the colonocyte in vitro, and the provision of preferred intestinal fuels has been shown to stimulate mucosal proliferation in vivo. This study determined whether chronic colonic infusion of butyrate or a combination of SCFA would stimulate intestinal mucosal growth in an animal deprived of its normal source of SCFA, fiber fermentation in the cecum. Adult male Sprague-Dawley rats were fed a fat- and fiber-free elemental liquid diet and underwent cecectomy, ileocolic anastomosis, and insertion of a proximal colonic infusion catheter. Rats were then assigned to receive either a continuous infusion of butyrate (20 mM, 40 mM, or 150 mM), SCFA (70 mM acetate + 35 mM propionate + 20 mM butyrate), or saline, or to receive no infusion. A seventh group underwent proximal colonic transection and reanastomosis. After 7 days, jejunal, ileal, and proximal colonic segments were analyzed for mucosal weight, protein, RNA, and DNA. In the colon, the 40-mM butyrate infusion resulted in significant elevations in all mucosal parameters relative to all three control groups, saline infusion, no infusion, and transection. Both the 20-mM butyrate and the SCFA groups showed increased colonic mucosal DNA compared to controls. In the jejunum and ileum, mucosal DNA content was significantly greater in the SCFA group than in the control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk factors in inflammatory bowel disease

A patient with inflammatory bowel disease may have several risk factors, including host defence and familial and environmental factors. Host defence factors include neutrophil and complement abnormalities and increased intestinal permeability. This may explain why elemental diets are effective treatment in Crohn's disease. Food is a major factor affecting the intestinal tract, and the considerable change in dietary habits during this century may explain why Crohn's disease has become more common. There is a geographic difference in the distribution of the disease. This could be due to difference in fish consumption. Fish oil has been shown to be effective in an uncontrolled study in the treatment of ulcerative colitis. This needs to be confirmed by ongoing controlled studies. Very few data have been published on the dietary habits of different countries. There is a need for a uniform dietary assessment that can be applied in a multicentre study. These studies would involve much co-operation but would yield important clues in the aetiology of inflammatory bowel disease.

Controlled trial of bowel rest and nutritional support in the management of Crohn's disease

To define the role of bowel rest as an independent variable from nutritional support a prospective, randomised controlled trial was undertaken in 51 patients with active Crohn's disease unresponsive to other medical management. Nutritional support for 21 days was randomised to total parenteral nutrition and nil by mouth (n = 17), defined formula diet administered through a nasogastric tube (n = 19), or partial parenteral nutrition and oral food (n = 15). Nutrient input in the first two groups provided 40 non-protein kcal/kg ideal body weight /d and 1g/ kg/d protein respectively, while the third group received 15 non-protein kcal/kg/d and 0.3 g/kg/d protein intravenously and ate unrestricted food. Clinical remissions occurred in 71% of patients on parenteral nutrition, in 58% on the defined formula diet and in 60% on partial parenteral nutrition; the probability for each group of being in remission at one year, after successful therapy was 42%, 55%, and 56% respectively. These differences were not significant. In patients with active Crohn's disease bowel rest was not a major factor in achieving a remission during nutritional support and did not influence outcome during one year's follow-up.

Luminal and metabolic regulation of jejunal amino acid absorption in the rat

Studies were carried out to determine the role of luminal amino acids and metabolic balance in in vivo amino acid absorption. Previous in vitro studies have shown that adaptation of amino acid transport is a complex phenomenon. In the first series of experiments, parenterally nourished rats received a 7-day jejunal infusion of either 3% aspartic acid, glutamine, lysine, valine, or mixed amino acids. A single-pass perfusion was performed to determine the effects of infusates on 5 mM valine, aspartic acid, and lysine absorption. Compared with controls receiving luminal saline, prior glutamine infusion increased valine absorption; prior valine, glutamine, and aspartic acid infusion significantly increased aspartic acid absorption; and prior valine and lysine infusion significantly increased lysine absorption. The mixed amino acid solution had no effect. The effects of metabolic balance were examined by comparing fasted rats with parenterally fed and orally fed rats. Within 24 h fasting significantly increased valine and aspartic acid absorption, despite a significant decrease in intestinal mass.

Enteral and parenteral nutrition in patients with enteric fistulas and short bowel syndrome

Significant advances in the use of enteral and parenteral nutrition in patients with either enteric fistulas or short bowel syndrome include increased usage of enteral nutrition because of its trophic effects on the gut and increased usage of both enteral and parenteral nutrition in the home setting. Current investigations are directed toward identifying gut-specific fuels and dietary and pharmacologic enhancement of nutrient utilization.

Defined formula diets alter jejunal and colonic uptake of lipids in rabbits with intact intestinal tract and following ileal resection

An in vitro technique was used to measure the jejunal and colonic uptake of fatty acids, decanol and cholesterol in sham-operated control (CONT) rabbits and in animals with a surgical resection of the distal half of the small intestine (RES). CONT and RES were fed standard Purina chow, Ensure, or Flexical HN for 2 weeks. The animals fed Ensure or Flexical HN consumed half the number of calories as the chow-fed rabbits and failed to gain weight. The mean of the jejunal dry weights were unchanged by diet or by ileal resection, although the height of the villi was lower in the animals fed the defined formula diets. Restricting chow intake to match the body weight gain of the animals fed Ensure or Flexical HN was associated with alterations in the uptake of lipids, but the pattern of changes was dissimilar to the pattern of changes observed in the resected animals or in the rabbits fed Ensure or Flexical HN. Ileal resection was associated with changes in the jejunal uptake of lipids and the influence of the defined formula diets on the uptake of short-, medium- and long-chain length fatty acids, decanol and cholesterol varied depending upon whether the animal had an intact intestinal tract or whether the animal had an ileal resection. It is concluded that the passive uptake of a homologous series of saturated fatty acids, cholesterol, and decanol into the jejunum and colon is modified by ad libitum feeding of Ensure or Flexical HN; the functional adaptation of the intestine and colon to dietary modification is influenced by the previous resection of the distal half of the small intestine; and these changes in the uptake of lipids are not explained solely by alterations in food intake, body weight gain, or intestinal morphology.

Nonspecific adaptation of jejunal amino acid uptake in the rat

Luminal nutrients are a major effector of intestinal adaptation. Amino acids are trophic to the intestine, but their role in regulating amino acid transport is not well documented. The presence of several distinct amino acid transport systems raises the question of whether adaptation is class-specific. Studies were carried out in parenterally nourished rats receiving a 7-day jejunal infusion of a 3% solution of either aminoisobutyric acid, aspartic acid, glutamine, histidine, lysine, or valine. While all amino acids were trophic to the intestine, their effects on the in vitro uptake of 0.1, 1.0 and 10.0 mM aspartic acid, lysine, and valine (representative acid, basic, and neutral amino acids) were variable and nonspecific. Compared to controls receiving either total parenteral nutrition alone or total parenteral nutrition plus luminal saline, prior lysine and aspartic acid infusion significantly increased in vitro uptake of all three amino acids tested, whereas valine had little effect on transport. No effect on transport was seen with glutamine (actively metabolized by the intestine as is aspartic acid), aminoisobutyric acid (a nonmetabolizable amino acid congener), or histidine (the most trophic amino acid). In conclusion, while individual amino acids cause an adaptation of amino acid uptake, the effects are nonspecific and independent of their metabolic or trophic potential.

Relationship between enteral glucose load and adaptive mucosal growth in the small bowel

Infusion of hyperosmolar glucose solutions into small bowel will prevent mucosal atrophy or stimulate mucosal growth in rats otherwise maintained on total parenteral nutrition (TPN). It is not certain whether this growth effect is related to the osmolarity of the solution or its total molecular load. Therefore, various concentrations of glucose and sodium salt solutions were studied for comparative effects on growth of small bowel mucosa. Male Sprague-Dawley rats (240 g) were maintained on TPN and infused continuously with either glucose or sodium chloride (2 and 0.6 ml/hr) or sodium sulfate (0.6 ml/hr) via a catheter placed in the mid-small intestine. Concentrations of infusion solutions ranged in osmotic pressure from 300 to 1500 mosmol/liter. Controls were TPN rats without infusion of any solution. Over a seven-day period, TPN rats receiving mid-gut infusions of 300 mosM saline gained 18.4 g in body weight. In TPN rats receiving mid-gut infusions of progressively greater concentrations of glucose, the additional total kilocalories per day resulted in greater body weight gain compared with the saline controls. After seven days, rats were killed, the small bowel removed, and divided into eight equal segments (segment 1, duodenum; segment 8, terminal ileum). Segment weight, mucosal weight, DNA, and protein concentration per segment were measured. Mid-gut infusions of 900 and 1500 mosM glucose solutions progressively increased mucosal mass in segments downstream from the site of infusion compared with 300 mosM glucose in water or 600 mosM glucose in saline which did not differ from any of the salt solutions or TPN alone.(ABSTRACT TRUNCATED AT 250 WORDS)