The effects of different bile salts on the absorption of fluid, electrolytes, and monosaccharides in the small intestine of the rat in vivo

Small Intestinal Bacterial Overgrowth-Pathophysiology and Its Implications for Definition and Management

The concept of small intestinal bacterial overgrowth (SIBO) arose in the context of maldigestion and malabsorption among patients with obvious risk factors that permitted the small bowel to be colonized by potentially injurious colonic microbiota. Such colonization resulted in clinical signs, symptoms, and laboratory abnormalities that were explicable within a coherent pathophysiological framework. Coincident with advances in medical science, diagnostic testing evolved from small bowel culture to breath tests and on to next-generation, culture-independent microbial analytics. The advent and ready availability of breath tests generated a dramatic expansion in both the rate of diagnosis of SIBO and the range of associated gastrointestinal and nongastrointestinal clinical scenarios. However, issues with the specificity of these same breath tests have clouded their interpretation and aroused some skepticism regarding the role of SIBO in this expanded clinical repertoire. Furthermore, the pathophysiological plausibility that underpins SIBO as a cause of maldigestion/malabsorption is lacking in regard to its purported role in irritable bowel syndrome, for example. One hopes that the application of an ever-expanding armamentarium of modern molecular microbiology to the human small intestinal microbiome in both health and disease will ultimately resolve this impasse and provide an objective basis for the diagnosis of SIBO.

In vitro Assessment of Chemical and Pre-biotic Properties of Carboxymethylated Polysaccharides From Passiflora edulis Peel, Xylan, and Citrus Pectin

This study aimed to determine the carboxymethylation effect of crude water-soluble polysaccharides of Passiflora edulis peel (WPEP), xylan (XY), and citrus pectin (CP). Their chemical and pre-biotic properties were also determined. The polysaccharides were carboxymethylated by reacting with chloroacetic acid and sodium hydroxide. The carboxymethylated and non-carboxymethylated polysaccharides were also used as pre-biotics to study the growth pattern of selected intestinal microflora. These polysaccharides substituted the glucose solution in culture media for culturing Lactobacillus brevis GIM1.773, Lactobacillus plantarum GIM1.19, Lactobacillus delbrueckii subsp. bulgaricus GIM1.155, and Streptococcus thermophilus GIM1.540. The results showed that the carboxymethylated polysaccharides c-XY, c-CP, and c-WPEP, had substitution degrees of 0.682, 0.437, and 0.439, respectively. The polysaccharides demonstrated resistance to digestion in the simulated human digestive models. The resistance to digestion was enhanced by carboxymethylation, especially the carboxymethylated CP and WPEP. The results also showed that the pre-biotic activities of the polysaccharides increased after carboxymethylation. The c-XY had a better pre-biotic effect than XY and the other carbohydrate samples. The findings suggested that carboxymethylated polysaccharides may be developed into novel pre-biotics and nutraceuticals that could promote growth of the probiotic strains.

Analysis of global transcriptional profiles of enterotoxigenic Escherichia coli isolate E24377A

Enterotoxigenic Escherichia coli (ETEC) is an important pathogenic variant (pathovar) of E. coli in developing countries from a human health perspective, causing significant morbidity and mortality. Previous studies have examined specific regulatory networks in ETEC, although little is known about the global effects of inter- and intrakingdom signaling on the expression of virulence and colonization factors in ETEC. In this study, an E. coli/Shigella pan-genome microarray, combined with quantitative reverse transcriptase PCR (qRT-PCR) and RNA sequencing (RNA-seq), was used to quantify the expression of ETEC virulence and colonization factors. Biologically relevant chemical signals were combined with ETEC isolate E24377A during growth in either Luria broth (LB) or Dulbecco's modified Eagle medium (DMEM), and transcription was examined during different phases of the growth cycle; chemical signals examined included glucose, bile salts, and preconditioned media from E. coli/Shigella isolates. The results demonstrate that the presence of bile salts, which are found in the intestine and thought to be bactericidal, upregulates the expression of many ETEC virulence factors, including heat-stable (estA) and heat-labile (eltA) enterotoxin genes. In contrast, the ETEC colonization factors CS1 and CS3 were downregulated in the presence of bile, consistent with findings in studies of other enteric pathogens. RNA-seq analysis demonstrated that one of the most differentially expressed genes in the presence of bile is a unique plasmid-encoded AraC-like transcriptional regulator (peaR); other previously unknown genetic elements were found as well. These results provide transcriptional targets and putative mechanisms that should help improve understanding of the global regulatory networks and virulence expression in this important human pathogen.

The problem of bacterial diarrhoea

The reported incidence of "pathogenic" bacteria, as judged by serotype, in the stools of children with acute diarrhoea has varied from 4 to 33% over the last twenty years. Techniques such as tissue culture provide a means for detecting enterotoxin-producing strains of bacteria, strains which often do not possess "pathogenic" serotypes. "Pathogenicity" requires redefinition, and the aetiological importance of bacteria in diarrhoea is probably considerably greater than previous reports have indicated. Colonization of the bowel by a pathogen will result in structural and/or mucosal abnormalities, and will depend on a series of complex interactions between the external environment, the pathogen, and the host and its resident bacterial flora. Enteropathogenic bacteria may be broadly classified as (i) invasive (e.g. Shigella, Salmonella and some Escherichia coli) which predominantly affect the distal bowel, or (ii) non-invasive (e.g. Vibrio cholerae and E. coli) which affect the proximal bowel. V. cholerae and E. coli elaborate heat-labile enterotoxins which activate adenylate cyclase and induce small intestinal secretion; the secretory effects of heat-stable E. coli and heat-labile Shigella dysenteriae enterotoxins are not accompanied by cyclase activation. The two major complications of acute diarrhoea are (i) hypernatraemic dehydration with its attendant neurological, renal and vascular lesions, and (ii) protracted diarrhoea which may lead to severe malnutrition. Deconjugation of bile salts and colonization of the small bowel with toxigenic strains of E. coli may be important in the pathophysiology of the protracted diarrhoea syndrome. The control of bacterial diarrhoea requires a corrdinated political, educational, social, public health and scientific attack. Bacterial diarrhoea is a major health problem throughout the world, and carries an appreciable morbidity and mortality. This is particularly the case during infancy, and in those developing parts of the world where malnutrition is common. This paper is concerned mainly with acute bacterial diarrhoea, and reviews the problem as a whole.

Involvement of enteric nerves in permeability changes due to deoxycholic acid in rat jejunum in vivo

AIM

Stress and Clostridium difficile toxin A increase epithelial permeability in the small intestine via vagus and visceral afferents, in turn activating mucosal mast cells. Bile acids also increase epithelial permeability but it is not known if nerves or mast cells are involved in this effect in the small intestine.

METHOD

In jejunum of anesthetized rats, the effects of hexamethonium and atropine on deoxycholic acid (DCA) induced fluid secretion and increase in epithelial permeability was therefore studied by determining the appearance and disappearance rates of 14C-mannitol and 51Cr-EDTA into and from a perfusion system containing 4 or 8 mm DCA and expressed as clearance.

RESULTS

DCA increased net fluid transport and appearance and to a less extent disappearance rates of the probes. Hexamethonium but not atropine, chronic denervation or the NO synthase inhibitor L-NNA did significantly decrease the appearance rate and net fluid secretion. The levels of the mast cell protease II (RMCP II) in perfusate and plasma were not increased by DCA. The clearance ratio Cr-EDTA/mannitol indicates that the plasma clearance of the permeability probes is partly secondary to net fluid transport only at higher DCA concentrations.

CONCLUSION

We conclude that the DCA effect on epithelial permeability is to a large part induced by intramural reflex(es) containing nicotinic receptors. The results also suggest that mast cell degranulation and NO release are not involved in the mechanism. This indicates that the nerve effect on intestinal paracellular permeability is not mediated by the mechanisms described for stress or Clostridium difficile toxin A.

Effects of guanylin and uroguanylin on rat jejunal fluid and electrolyte transport: comparison with heat-stable enterotoxin

The effects of rat guanylin, human guanylin, human uroguanylin and STa on net fluid and electrolyte transport in the closed jejunal loop were compared in anesthetized rats. STa administered into the lumen caused a concentration-dependent (10(-8) to 10(-6) M) inhibition of net fluid and NaCl absorption in the jejunal loop. Uroguanylin had a similar but weaker effect than STa. Both rat and human guanylin inhibited fluid and NaCl absorption only at 10(-6) M. Their order of potency was STa > human uroguanylin > rat guanylin = human guanylin. Changing the luminal pH from 5 to 8 failed to affect the action of guanylin on fluid absorption. Both STa and uroguanylin, but not guanylin, increased the luminal pH by stimulating bicarbonate secretion. Pretreatment of the jejunal loop with guanylin (10(-6) M) 5 min before the instillation of STa (10(-7) M) significantly reduced the inhibitory effect of STa on fluid absorption. It is concluded that guanylin and uroguanylin administered into the rat jejunal lumen have an STa-like action on fluid and electrolyte transport. Guanylin may act as an endogenous antagonist of STa in the rat jejunum and prevent excessive fluid loss by STa.

Abnormal leukotriene C4 released by unaffected jejunal mucosa in patients with inactive Crohn's disease

The mucosal release of inflammatory mediators is enhanced in active inflammatory bowel disease. This study examines whether leukotriene C4 production occurs in apparently unaffected segments of the gut. The intraluminal release of leukotriene C4 was determined by jejunal perfusion in seven healthy controls, in nine patients with chronic ulcerative colitis, and in 13 patients with Crohn's disease (six with ileal disease, and seven with only colonic). All patients were in clinical remission and none of them had evidence of jejunal involvement. Mild intraluminal irritation with a 2.5 mmol/l deoxycholic acid solution was induced to stimulate local inflammatory mechanisms. The release of DNA (a marker of mucosal desquamation) and prostaglandin E2 (PGE2) was simultaneously measured. Jejunal release of DNA was higher in Crohn's disease patients than in ulcerative colitis or healthy controls. Basal release of PGE2 was similar in the three groups of patients. Basal release of leukotriene C4 was considerably enhanced, however, in Crohn's disease patients compared with healthy controls. In ulcerative colitis patients, basal leukotriene C4 release was non-significantly different from controls. Bile acid perfusion stimulated PGE2, leukotriene C4, and DNA release in all groups studied, but leukotriene C4 release was significantly higher in Crohn's disease patients. It is concluded that in inactive Crohn's disease there is an enhanced intraluminal release of leukotriene C4 in apparently unaffected segments of proximal small bowel, which may reflect fundamental changes in the function of the gut mucosal barrier.

Modulation of fluid absorption and the secretory response of rat jejunum to cholera toxin by dietary fat

To study the effects of dietary fat on jejunal water and ion absorption and on cholera toxin-induced secretion, 3 week old Sprague Dawley rats were fed isocaloric diets. Forty per cent of the total calories were given as fat, as butter (high saturated fat), olive oil (high monounsaturated fat), or corn oil (high polyunsaturated fat), with one group on low fat (10% of calories) standard laboratory diet as controls. During in vivo jejunal perfusion studies we found that (i) a polyunsaturated fat (corn oil) supplemented diet improves jejunal absorption of water and electrolytes and these changes are independent of the observed concentrations of luminal prostaglandins; (ii) high dietary fat appreciably reduced the secretory response to cholera toxin, probably without fundamentally changing the mechanism by which cholera toxin induces secretion. We conclude that dietary fat composition altered the permeability and transport characteristics of the small intestine. This observation might have relevance to some human diarrhoeal disorders.

Morphological and functional recovery following exposure to deoxycholic acid. A study in the rat small intestine in vivo

Whereas many studies deal with teh deleterious effects of unconjugated deoxycholic acid on epithelial morphology, few are concerned with the reversibility of these effects, the subject of the present study. Tied jejunal loops in the rat were incubated for 30 minutes with deoxycholic acid (2.5-20 mmol/litre) in isotonic solution. Immediately after this treatment, or after a subsequent recovery period of 15 or 150 minutes following wash out of the bile acid, the loops were excised, fixed and examined by light microscopy and scanning electron microscopy. Deoxycholic acid produced epithelial lesions whose severity and reversibility depended on the concentration applied. However, even the severely affected epithelium obtained by treatment at 10-20 mmol/litre was reverted to normal within 150 minutes, and a substantial normalisation was observed already after 15 minutes. An exception to this rapid restoration of epithelial morphology and integrity was noted in villi which had suffered necrosis of lamina propria. The revertion of epithelial pathology was paralleled with a normalisation of glucose absorption, of the potassium ion and protein content of the loop fluid, and of the paracellular epithelial permeability as measured with 3-H-poly-ethylenglycol. Morphometry showed that deoxycholic acid caused villous atrophy without affectin the crypt length. The extent and reversibility of this atrophy depended on dose and recovery time as above. It is suggested that the remarkably fast morphological restitution proceeds mainly by process involving cellular remodelling and migration.

Alteration of methotrexate metabolism in rats by administration of an elemental liquid diet. II. Reduced toxicity and improved survival using cholestyramine

The administration of an elemental, chemically defined liquid diet to rats significantly enhanced gastrointestinal toxicity associated with methotrexate administration compared with rats fed a regular chow diet. Chemotherapy induced enteritis is potentially enhanced by the abrasive effect of bile acids on the susceptible cells of the small bowel mucosa. This study evaluated the interactions of methotrexate and cholestyramine in vitro. An additional goal was to evaluate the effects of cholestyramine on animal survival and drug pharmacokinetics in rats given an elemental, chemically defined liquid diet. In vitro binding of cholestyramine to methotrexate increased in a linear fashion at varying concentrations of both drugs in phosphate buffer solution (r greater than 0.84, P less than 0.001) and in bile which was not influenced by pH (range 5-8). The addition of cholestyramine to an elemental liquid diet significantly improved survival following methotrexate administration (20 mg/kg IP bolus) compared with rats fed an elemental liquid diet alone (P less than 0.02). Both elemental liquid diets, either with or without cholestyramine, delayed serum and biliary clearance of methotrexate up to 72 hours compared with rats fed a regular chow diet. However, rats fed an elemental liquid diet with added cholestyramine had significantly lower levels of methotrexate in serum from the systemic and portal venous circulation at 48 hours (P less than 0.03) and in bile at 48 (P less than 0.02) and 72 hours (P less than 0.05) following methotrexate administration. The addition of cholestyramine to an elemental liquid diet improves survival and reduces gastrointestinal toxicity following methotrexate administration, by binding methotrexate in bile and reducing the delay in systemic clearance of the drug. By binding to intraluminal bile acids, cholestyramine may also have a locally protective effect on the mucosal cells of the small intestine following methotrexate administration. Cholestyramine may be of clinical benefit in patients receiving high-dose methotrexate regimens as an adjunct to leucovorin rescue.

Involvement of the enteric nervous system in the intestinal secretion induced by sodium deoxycholate and sodium ricinoleate

Rat small intestine was continuously perfused for up to 3 h with two different concentrations of sodium deoxycholate (4 and 8 mM) or with sodium ricinoleate (6 mM). The 4-mM bile salt solution produced a secretion that developed to a maximal rate within 3 h, whereas the maximal rate was reached within 1 h with the 8-mM bile salt solution. Hexamethonium, a ganglionic blocker, and lidocaine, a local anesthetic, always reduced the net fluid secretion to approximately zero irrespective of the rate of bile-salt-induced secretion, the concentration of the bile salt, or the perfusion time. Fluid secretion induced by sodium ricinoleate was, like the bile-salt-induced secretion, markedly inhibited by hexamethonium and lidocaine but not by atropine. It is concluded that the rate of secretion induced by the bile salt is related to the monomer concentration of free bile salt molecules in close proximity to or within the intestinal epithelium. The intestinal fluid secretion is mainly due to stimulation of an active secretory process via an activation of enteric nerves. Sodium ricinoleate evokes secretion via similar nervous reflex mechanisms.

Human milk in the management of protracted diarrhoea of infancy

Eleven of 13 children with the protracted diarrhoea syndrome of infancy were successfully treated with human milk. All the infants, who were severely malnourished, had deteriorated while fed on a wide range of highly modified formulas. Seven infants responded promptly with cessation of weight loss and diarrhoea; in four others, human milk was used to re-establish oral nutrition after a period of intravenous nutrition when all other measures had failed. Two children did not respond to human milk. Despite its high lactose content, human milk has nutritional and immunological properties that may reverse many of the factors thought to cause the protracted diarrhoea syndrome, and we conclude that it has an important role in management of this syndrome and may obviate the need for intravenous nutrition as a life saving measure.

Studies on hydragogue drugs: light and electron microscopic examination of the isolated rat colonic mucosa exposed to deoxycholic acid and synthetic surfactants

Sacs of the stripped and everted, isolated descending rat colon were incubated for 2 hours in presence of the following surfactants at the mucosal side: Dodecylsulphate (DDS), dioctylsulphosuccinate (DOSS), cetrimonium bromide (CTMAB), Triton X100 and deoxycholic acid (DOC). After tissue fixation, the sacs were processed for light microscopy (LM) and for scanning (SEM) and transmission (TEM) electron microscopy. All three methods revealed that DOSS (1.3 X 10(-4) and 2.6 X 10(-4) mol/l, CTMAB (5 X 10(-5) and 1 X 10(-4) ) and Triton (2 X 10(-5), 5 X 10(-5) and 1 X 10(-4) ) caused only minor or moderate changes compared to parallel controls, as did also DDS at 1 X 10(-5) and 2 X 10(-5) mol/l. DDS at 2 X 10(-4) and 4 X 10(-4) mol/l and DOC at 1.5 X 10(-4) and 3 X 10(-4) mol/l caused more prominent changes. LM showed swollen, vacuolated cells with pycnotic nuclei; many of these cells seemed to be extruded. According to SEM, cells thus affected were most abundantly localized to the normal extrusion zone at the borders of the crypt-surface epithelial cell units. DOC tended to cause a more generalized affection within the units than DDS. In spite of these deleterious effects, gaps corresponding to missing epithelial cells were not observed. TEM indicated the mechanism responsible for restoration of epithelial continuity in spite of extensive cell loss: The remaining epithelial cells seemed to flatten out and re-establish cell-to-cell contact by pseudopod formation along the basement lamina. This repair mechanism seemed to operate at a rapid rate; however, incomplete closure of cellular gaps i.e. small denuded parts of the basement lamina were occasionally observed. The results of this study are discussed in relation to a functional study under identical experimental conditions (Gastroenterol. Clin. Biol. 1981, 5, 124), in which these surfactants caused a significant alteration of normal colonic transport function.

Effects of lysophosphatidylcholine on jejunal water and solute transport in the rat in vivo

The effects of lysophosphatidylcholine on jejunal water and solute transport were studied in vivo in the rat. Five mM lysophosphatidylcholine significantly reduced absorption of water, electrolytes and glucose (P less than 0.05) and 10 mM lysophosphatidylcholine induced net fluid secretion. The effects of 10 mM lysophosphatidylcholine were significantly reduced in the presence of 5 mM phosphatidylcholine (P less than 0.05) and 2 mM cholesterol (P less than 0.05). The fractional absorption of lysophosphatidylcholine decreased with increasing concentration of the detergent in the perfusion solution. Increasing concentrations of taurocholate in the perfusion solutions potentiated the effects of lysophosphatidylcholine (P less than 0.01), although 10 mM taurocholate by itself had no significant effect on intestinal water and electrolyte transport. The data establish that lysophosphatidylcholine, a zwitterionic detergent, affects intestinal transport in the same way as bile acids, fatty acids and synthetic cationic or nonionic detergents. By comparison with the response of the human jejunum to taurodeoxycholate, it is likely that lysophosphatidylcholine generated during the normal process of digestion has an effect on intestinal water and solute transport in man.

Loperamide: studies on its mechanism of action

The effects of loperamide on net solute and water absorption, and prostaglandin E2 (PGE2) and cholera toxin-induced secretion were studied in the rat jejunum using an in vivo steady-state perfusion technique. Loperamide stimulated absorption of fluid, electrolytes, and glucose and reversed PGE2 and cholera toxin-induced secretion to absorption; this opiate analogue had no effect on cholera toxin stimulation of adenylate cyclase activity or the rise of tissue cyclic AMP (cAMP) concentrations. The opiate antagonist, naloxone, reduced the antisecretory effects of loperamide without affecting tissue levels of cAMP. These results indicate that loperamide inhibits PGE2 and cholera toxin-induced secretion, and that this phenomenon is independent of any direct effect that cholera toxin has on the adenylate cyclase system. The action of naloxone suggests, but does not prove, that loperamide exerts its effect via opiate receptors.

Effect of glucose on jejunal water and solute absorption in the presence of glycodeoxycholate and oleate in man

Jejunal perfusion studies were performed in 12 healthy volunteers to study the effects of 14 and 56 mM glucose on fluid secretion induced by 5 mM glycodeoxycholate on 7 mM oleate. Glucose enhanced water absorption under control conditions and reduced water secretion induced by glycodeoxycholate or oleate (P less than 0.01). As has been observed previously, glycodeoxycholate and oleate inhibited glucose absorption (P less than 0.001) and significant linear relationships existed between net water movement and glucose absorption. Glycodeoxycholate also reduced the absorption of 14 mM arabinose (P less than 0.05) and oleate reduced the absorption of 56 mM mannitol (P less than 0.05). Reduced solute absorption in the presence of glycodeoxycholate and oleate, therefore, cannot be attributed to an effect on active transport alone. The relationships between sodium transport and water absorption varied with the glucose concentration in the perfusion solutions. Similarly, the relationships between glucose absorption and sodium absorption varied with glucose concentration. The data suggest that a significant amount of glucose can be absorbed without concomitant absorption of sodium. The data indicate that glucose absorption can stimulate water absorption directly without the mediation of sodium and that water movement follows glucose at a rate which maintains isotonicity.

Specific antigen exclusion and non-specific facilitation of antigen entry across the gut in rats allergic to food proteins

The intestinal absorption of ovalbumin and beta-lactoglobulin was measured in Hooded Lister rats which had previously been made allergic to ovalbumin, and in unimmunized controls. The antigens were introduced both together and separately into closed intestinal loops. Absorption of free ovalbumin, but not beta-lactoglobulin, was reduced in rats with anti-ovalbumin antibody, demonstrating antigen-specific immune exclusion despite the presence of reaginic antibody. In contrast, the absorption of beta-lactoglobulin was enhanced by the presence of ovalbumin in rats with IgE anti-ovalbumin, but not in unimmunized controls. These results suggest that macromolecular absorption may be increased in an antigen non-specific way in food allergy.

Increased cell loss in the human jejunum induced by laxatives (ricinoleic acid, dioctyl sodium sulphosuccinate, magnesium sulphate, bile salts)

Two conjugated bile salts (10 mmol/l sodium glycocholate, 10 mmol/l sodium taurodeoxycholate) and three laxatives (30 mmol/l magnesium sulphate, 10 mmol/l ricinoleic acid, 2 mmol/l dioctyl sodium sulphosuccinate) were tested on seven subjects with no intestinal lesions in 14 experiments by intestinal perfusion of the jejunum. A 25 cm segment was studied. Each solution was perfused at the rate of 10 ml/min. Water and electrolyte fluxes, losses of deoxyribonucleic acid (DNA), and intestinal cell enzyme activity were measured in the fluids collected. All the laxatives and bile salts tested (except sodium glycocholate) induced water and electrolyte secretion, a rise in intraluminal DNA loss, and enzyme activity. It was possible to establish a significant correlation (p less than 0.001) between the amounts of water fluxes and DNA loss under the effect of dioctyl sodium sulphosuccinate and ricinoleic acid.

Intestinal filtration as a consequence of increased mucosal hydraulic permeability. A new concept for laxative action

Two mechanisms have been proposed to explain the secretory action of laxative compounds in the intestine: 1. increase of the intracellular amount of cyclic adenosine monophosphate due to stimulation of the adenylate cyclase system and 2. inhibition of intestinal transfer processes, in particular the Na,K-ATPase activated sodium absorption. In a set of in vivo and in vitro experiments in rat colon it could be demonstrated that dihydroxy bile acids (deoxycholate) and diphenolic laxatives (oxyphenisatin) enhance the hydraulic permeability of the mucosal tissue. The permeability changes take place--and there is good experimental evidence--at the zonulae occludentes which bind the epithelial cells together at their luminal borders. Due to laxative action the hydraulic permeability of the colonic mucosa increases to such an extent that according to the Starling forces the normal subepithelial hydrostatic pressure is a sufficient driving force to reverse net sodium, chloride, and water absorption into net secretion. A new concept of "intestinal filtration as a consequence of increased mucosal hydraulic permeability" is proposed to explain the laxative action of deoxycholate and oxyphenisatin in the colon. The question whether inhibition of Na,K-ATPase activity, cyclic AMP-mediated secretion or increased hydraulic permeability of the colonic mucosa are causatively linked to and quantitatively meaningful in intestinal secretion remains open.

Do low doses of deoxycholate modify the release of rat jejunal brush border hydrolases?

The in-vivo effects of sodium deoxycholate (DOC) at low concentrations on the release of protein and some brush border hydrolases, sucrase (SA), maltase (MA), leucine aminopeptidase (LA), alkaline phosphatase (AP), have been investigated in the rat by a jejunal perfusion technique. During perfusion with DOC (0.125 or 0.25 mmol/l), enzyme release was not enhanced. After removal of DOC from the perfusion solution with 0.125 mmol/l DOC, there was a steady release of SA, MA and AP although enzyme release was increased linearly in the control and the 0.25 mmol/l DOC groups. The results also confirm the deep localization of AP within the membrane.

[The effect of unconjugated bile salts on the intestinal absorption of electrolytes and water in the proximal jejunum. Studies in conscious rats (author's transl)]

With an in vivo-perfusion-technique the influence of unconjugated bile salts (cholate, desoxycholate) on the net electrolyte and volume absorption is studied in the jejunum of conscious rats. The applied doses correspond to physiological concentrations in the intestine of rats. Control experiments were performed in the same animal. Cholate and desoxycholate diminish the net electrolyte and volume absorption resp. cause a net secretion. The effects are largely reversible. The extent of net volume absorption depends on the applied dose of each bile salt. The possible mode of action of unconjugated bile salts on the electrolyte and water absorption in the small intestine is discussed.

Duodenal bile acids in infants with protracted diarrhoea

Bile acids were estimated in the duodenum of infants with protracted diarrhoea and compared with those in a control group. Significantly lower levels of total bile acids were found in infants with protracted diarrhoea, a finding which may be due to ileal dysfunction. Low concentrations of total bile acids may contribute to the poor nutritional state of these patients by impairing the normal digestion and absorption of dietary fat and fat-soluble vitamins. The absence of deconjugated bile acids in the duodenal juice of most infants with protracted diarrhoea suggests that they do not contribute significantly to the pathophysiology of this disorder.

Intestinal bile salts in cystic fibrosis: studies in the patient and experimental animal

The quantitative and qualitative distribution of bile salts in the duodenal juice of 13 patients with cystic fibrosis (CF) was studied after a test meal. The effects of triolein (TO), bovine serum albumin (BSA), and ricinoleic acid (RA) on the absorption of taurocholate (TCA) in the distal ileum of the rat in vivo was also studied. The mean (and ranges) of total bile salt concentrations, glycine: taurine conjugate ratios, and percentage of dihydroxy bile salts in the patients with CF and pancreatic insufficiency were 3.5 (1.3--6.6) mmol/l, 8.6 (greater than 10-3.1), and 37 (10--60) compared with control values of 7.4 (3.0--16.0) mmol/l, 3.0 (1.3--4.5), and 61 (52--70) respectively. The differences between the control and CF values were statistically significant (P less than 0.01--P less than 0.001). Three of the 13 CF patients had total bile salt concentrations less than 2 mmol/l, 8 had much higher glycine: taurine ratios, and 8 had a reduced percentage of dihydroxy bile salts. In 2 patients with normal pancreatic enzyme activities, duodenal bile salts were both quantitatively and qualitatively normal. TO (10 and 30 mmol/l), BSA (3%), and RA (5 mmol/l) had no inhibitory effect on the ileal absorption of TCA. These results show pronounced abnormalities of duodenal juice bile salts in CF with pancreatic insufficiency consistent with a broken enterohepatic circulation (EHC); such abnormalities may contribute to defective lipid absorption in CF. The data in the experimental animal do not support the suggestion that unhydrolysed dietary substrates play a role in the pathophysiology of the broken EHC.

In vivo reversibility of the jejunal glucose and cation transport alteration caused by intraluminal surfactants in the rat

Tied jejunal loops in anaesthetized rats were under standardized conditions pre-exposed for 30 min. with Tyrode solution containing surfactants. 5, 20 or 150 min. after wash out of bulk surfactant, the loops were re-instilled with Tyrode containing glucose at 5--15 mmol/l. Net glucose, sodium and potassium transport were studied for 15 min. by changes in intraluminal amounts, and compared with results obtained in control rats. The surfactants (mmol/l) tested were the anionics dioctylsulphosuccinate (5.6) and dodecylsulphate (8.5--17), the cationics cetrimonium bromide (2.1--4.1) and benzalkonium chloride (2.1), the nonionics Triton X100 (0.25%) and Lubrol WX (0.25--0.5%) plus cholic acid (4.9) and desoxycholic acid (1.3--2.5). In most cases, the glucose transport was normal or fairly normal after 150 min., most of the restoration taking place shortly after surfactant removal. However, Lubrol in particular caused more irreversible effects. Generally, the changes in net cation transport tended to be less easily reversible than the alteration in glucose transport. In so far as a normal or near to normal glucose transport is unlikely to occur unless both functional and structural integrity of the epithelium is preserved, the results indicate that in most cases there is but insignificant epithelial damage under the experimental conditions. Since, furthermore, these surfactants can interact with glucose transport in the same technique even at lower concentration and shorter incubation time than used here, it is concluded that the interaction of surfactants with intestinal transport is not neccessarily linked to gross histo-pathological changes.

Inhibition by morphine of prostaglandin-stimulated fluid secretion in rat jejunum

1 Anesthetized rats (225 to 300 g) were used to study the inhibitory effect of morphine on fluid secreted by the small intestine. 2 Small intestinal fluid secretion was stimulated by infusion of prostaglandin E1 (PGE1) into the aortic arch, the jejunum being more sensitive than the ileum. Infusion of PGE1 2 microgram/min caused maximal net fluid secretion in the jejunum but inhibited net fluid absorption in the ileum. 3 Morphine caused a dose-related inhibition of maximal PGE1-stimulated fluid secretion in the jejunum. At the higher doses of morphine used (5 to 20 mg/kg) the fluid transporting function of the jejunum was restored almost to normal net absorption. 4 The inhibitory effect of morphine on PGE1-stimulated fluid secretion was antagonized by naloxone. Naloxone caused a parallel shift to the right of the dose-response curve for morphine. 5 Two other narcotic analgesics were assayed relative to morphine and their descending order of potency was oxymorphone greater than morphine greater than pethidine. 6 It is suggested that the antisecretory effect of morphine in the small intestine may contribute to its efficacy as an anti-diarrhoeal drug. Further studies on the rat jejunum may show it to be a useful model for predicting narcotic drug activity and as such, may give some insight into the mechanisms of action of these drugs.

Protracted diarrhoea in infancy. Analysis of 82 cases with particular reference to diagnosis and management

Eighty-two cases of protracted diarrhoea in infancy presenting over a 6-year period have been analysed, with particular reference to diagnosis and management. The patients fell into 1 of 2 categories according to whether a specific diagnosis was established or not. A diagnosis (category 1) was established in 59 (72%), the commonest diagnoses being coeliac disease (33-2%), secondary disaccharide intolerance (12-2%), and cows' milk protein intolerance (12-3%). Other diagnoses included primary sucrase-isomaltase deficiency, Shwachman's syndrome, ulcerative colitis, ganglioneuroma, defective opsonization, staphylococcal pneumonia, and Hirschsprung's disease. Despite intensive investigation in diagnosis could not be established in 23 (28%) infants (category 2). Age of onset of symptoms in this group tended to be earlier than in category 1 patients, and 6 (7%) presented with diarrhoea dating from birth. Of particular interest in these 6 patients was the high incidence of associated extraintestinal anomalies, and of sibs who had died after protracted diarrhoea dating from birth. 4 of these 6 infants died, accounting for a mortality of 5% for the whole series. The remaining 17 (21%) patients in category 2 presented at a mean age of 4-9 weeks with a range of 1-18 weeks. All these 17 patients made an excellent response after institution of a chicken-based dietary formula, the details of which are presented. The pathophysiological mechanisms which may be operating in infants with protracted diarrhoea are discussed.

Characterization of microsomal choloyl-coenzyme A synthetase

Choloyl-CoA synthetase (EC 6.2.1.7) was characterized for the first time under appropriated assay conditions. The p/ optimum for the reaction is pH 7.2.-7.3. The reaction has an absolute requirement for bivalent cation. Several different metal ions fulfil this requirement, but Mn2+ and Mg2+ were the most effective. The KAppm (apparent Km) for CoA, extrapolated from kinetic data, is 50 micronM, but in fact the rate of reaction is increased little by concentrations of CoA above 25 micronM. The KAppm for ATP is 600 micronM. High concentrations of ATP appear to cause substrate inhibition. The KAppm for cholate was 6 micronM. The enzyme was inhibited by treating the microsomal fraction with N-ethylmaleimide. The inclusion of various conjugated and unconjugated bile salts in the assay also inhibited the enzyme. Unconjugated bile salts were more potent inhibitors than the conjugated bile salts. High concentrations of oleic acid inhibited the enzyme. The properties of choloyl-CoA synthetase were not modified by alterations of the properties of the lipid phase of the microsomal membrane. Treatment with phospholipase A did not alter activity directly. Triton N-101 and Triton X-100 also were without effect on activity, and the enzyme was insensitive to temperature-induced phase transitions within the lipid portion of the membrane. The enzyme can be solubilized from the microsomal membrane in an active form by treatment with Triton N-101.

Transfer of sodium and water through isolated rat colonic mucosa under the influence of deoxycholate and oxyphenisatin

1. The influence of oxyphenisatin (OP), a diphenolic laxative, and deoxycholate (DC) on the transfer of sodium and water in an everted sac preparation of stripped rat colon was investigated. 2. OP (10(-5) M, mucosal side) and DC (3 X 10(-4) M, mucosal side) completely blocked net water and sodium absorption. Net movements from the serosal to the mucosal side could not be induced by higher concentrations of the drugs. 3. Unidirectional sodium movements in both directions were increased by OP and DC. 4. The effect of DC on the sodium flux from the serosal to the mucosal side was reversible. 5. The potassium content of the mucosal epithelium was not changed by DC and OP. 6. The integrity of the epithelium, as judged by light microscopy, was not disturbed by either drug under the experimental conditions. 7. It is concluded that DC and OP do not interfere with active transport mechanisms but increase the permeability of the epithelium to sodium.

Factors affecting the absorption of vitamin K-1 in vitro

Factors which might affect the absorption of vitamin K of dietary origin were investigated using everted small bowel sacs. Increasing the bile salt concentration to 20 mM or the addition of long chain fatty acids, monoolein, or lecithin all resulted in significant (P less than 0-05) decrease in the absorption rate of the vitamin. The addition of 2-5 mM short and medium chain fatty acids did not change the absorption rate of vitamin K-1 (P greater than 0-05). The absorption rate of vitamin K-1 appears to be modified by the presence of compounds in the incubation medium which either alter the partition of the vitamin between the micelle and the cell membrane or which change the permeation characteristics of the compound through the unstirred water layer or modify the physical characteristics of the cell membrane itself. It is possible that some of the above factors modify the absorption of lipid soluble compounds in general.

The effects of pure and micellar solutions of different bile salts on mucosal morphology in rat jejunum in vivo

The effects of pure and micellar solutions of different bile salts on mucosal morphology have been investigated in rat jejunum using a closed-loop technique; the effects of an anionic dihydroxy steroid antibiotic, fusidic acid, have also been studied. Mucosal changes were assessed by light-microscopical appearances and quantified by determining surface to volume ratios (c/1h). The unconjugated dihydroxy bile salts, chenodeoxycholate and deoxycholate (DC), produced similar and gross structural changes at concentrations of 2-5 to 5 mM, as judged by mucosal appearances, but not at 1 mM; the unconjugated trihydroxy bile salt cholate and a variety of di- and trihydroxy conjugated salts produced no changes at concentrations of 5 to 20 mM. Fusidate (5 mM) produced similar changes to 5 mM DC. Compared with control values DC (1,2-5 and 5 mM) and fusidate (5 mM) produced highly significant (P less than 0-001) reductions in c/1h ratios. DC-induced damage was completely abolished by mixed micellar solutions, whereas pure micellar solutions provided no protection. These results indicate, (i) a molecular specificity for bile salt-induced mucosal damage, and (ii) that the effects of the unconjugated dihydroxy species on mucosal structure depends not only on their intraluminal concentrations, but also on the relative concentrations of conjugated bile salts and lipids present in the lumen.

Regional differences in the effect of bile salts on absorption by rat small intestine in vivo

1. The hypothesis that endogenous bile salts influence water absorption in rat small intestine was tested in vivo. 2. Net water transport was measured under steady-state conditions during single-pass infusion of segments from three regions of the small intestine. Each segment served as its own control. 3. Delipidated rat bile, and solutions of the principal bile salts of the rat, taurocholate and glycocholate, reduced absorption in the proximal jejunum but not in the distal ileum. 4. 1-Palmitoyl,2-oleoyl lecithin, an important biliary lecithin, counteracted the inhibitory effect of taurocholate and of glycocholate on absorption. The presence of biliary lecithins probably explains why whole rat bile did not depress water absorption in the proximal jejunum. 5. Net water transport in the distal jejunum was inversely related to log10 (taurocholate concentration). 6. Endogenous bile salts may help to maintain the fluidity of the contents of the mid-small intestine in the rat after biliary and dietary lecithins have been absorbed.

Bile salt alteration of ion transport across jejunal mucosa

The effect of conjugated dihydroxy and trihydroxy bile salts on electrolyte transport across isolated rabbit jejunal mucosa was studied. Both taurochenodeoxycholic acid and taurocholic acid increased the short-circuit current (Isc) in bicarbonate-Ringer solution but not in a bicarbonate-free, chloride-free solution. Taurochenodeoxycholic acid was significantly more effective than taurocholic acid in increasing Isc. The presence of theophylline prevented the taurochenodeoxycholic acid- and taurocholic acid-induced increase in Isc. Transmural ion fluxes across jejunal mucosa demonstrated that 2 mM taurochenodeoxycholic acid decreased net Na+ absorption, increased net Cl- secretion and increased the residual flux (which probably represents HCO3- secretion). These studies support the hypothesis that cyclic AMP may be a mediator of intestinal electrolyte secretion.

A comparative study on the effects of different bile salts on mucosal ATPase and transport in the rat jejunum in vivo

The effects of deoxycholate, taurocholate and cholate on transport and mucosal ATPase activity have been investigated in the rat jejunum in vivo using closed-loop and perfusion techniques. In the closed-loops, 5 mM deoxycholate selectively inactivated (Na+ + K+)-ATPase, and net secretion of Na+ induced by 2.5 mM deoxycholate was due to reduced lumen to plasma flux of the ion; deoxycholate (2.5 mM) produced marked inhibition of 3-0-methylglucose transport. Luminal disappearance rates of deoxycholate (60.5 plus or minus 2.9% per g wet st of gut) greatly exceeded those of taurocholate (4.3 plus or minus 1.0). In the perfusion studies 1 mM deoxycholate induced net secretion of water, Na+ and C1-, and inhibited active glucose transport; concomitantly "total" ATPase, (Na+ + K+)-ATPase, and Mg-2+-ATPase were inhibited. At higher concentrations (5 mM) deoxycholate stimulated Mg-2+-ATPase activity. Taurocholate and cholate at 1mM had no effect on transport of (Na+ + K+)-ATPase. Mucosal lactase, sucrase and maltase activities were not affected by 1 mM deoxycholate, taurocholate or cholate. These results suggest that deoxycholate inhibits sodium-coupled glucose transport by inhibition of (Na+ + K+)-ATPase at the lateral and basal membranes of the epithelial cell, rather than from an effect at the brush-border membrane level.

Mechanisms of lipid loss from the small intestinal mucosa

Many water-soluble compounds have been shown to pass from the small intestinal mucosa into the lumen. In this work, the loss of lipids from the mucosa was investigated by perfusion experiments in rats, using 0-15M NaCl or buffer solutions over range of pH, with or without the addition of 5-7 or 11-4mM taurocholic acid. Perfusates were extracted for the estimation of individual lipids and for DNA, which is a measure of cell loss. The results suggest that free fatty acids reach the lumen by diffusion and that their solubility in the luminal fluid is a factor determining their rate of loss. Triglycerides, cholesterol, phosphatidyl ethanolamine, and phosphatidly choline are present onlyas the result of desquamation of mucosal cells.