Roles of the gut in the metabolic syndrome: an overview

The metabolic syndrome is a cluster of risk factors (central obesity, hyperglycaemia, dyslipidaemia and arterial hypertension), indicating an increased risk of diabetes, cardiovascular disease and premature mortality. The gastrointestinal tract is seldom discussed as an organ system of principal importance for metabolic diseases. The present overview connects various metabolic research lines into an integrative physiological context in which the gastrointestinal tract is included. Strong evidence for the involvement of the gut in the metabolic syndrome derives from the powerful effects of weight-reducing (bariatric) gastrointestinal surgery. In fact, gastrointestinal surgery is now recommended as a standard treatment option for type 2 diabetes in obesity. Several gut-related mechanisms that potentially contribute to the metabolic syndrome will be presented. Obesity can be caused by hampered release of satiety-signalling gut hormones, reduced meal-associated energy expenditure and microbiota-assisted harvest of energy from nondigestible food ingredients. Adiposity per se is a well-established risk factor for hyperglycaemia. In addition, a leaky gut mucosa can trigger systemic inflammation mediating peripheral insulin resistance that together with a blunted incretin response aggravates the hyperglycaemic state. The intestinal microbiota is strongly associated with obesity and the related metabolic disease states, although the mechanisms involved remain unclear. Enterorenal signalling has been suggested to be involved in the pathophysiology of hypertension and postprandial triglyceride-rich chylomicrons; in addition, intestinal cholesterol metabolism probably contributes to atherosclerosis. It is likely that in the future, the metabolic syndrome will be treated according to novel pharmacological principles interfering with gastrointestinal functionality.

Local expression of AP/AngIV/IRAP and effect of AngIV on glucose-induced epithelial transport in human jejunal mucosa

BACKGROUND

Recently it was shown that the classic renin-angiotensin system (RAS) is locally expressed in small intestinal enterocytes and exerts autocrine control of glucose transport. The aim of this study was to investigate if key components for the Angiotensin III (AngIII) and IV (AngIV) formation enzymes and the AngIV receptor, insulin-regulated aminopeptidase (IRAP), are present in the healthy jejunal mucosa. A second aim was to investigate AngIV effects on glucose-induced mucosal transport in vitro.

MATERIAL AND METHODS

Enteroscopy with mucosal biopsy sampling was performed in healthy volunteers. ELISA, Western blotting and immunohistochemistry were used to assess the protein levels and localization. The functional effect of AngIV was examined in Ussing chambers.

RESULTS

The substrate Angiotensin II, the enzymes aminopeptidases-A, B, M as well as IRAP were detected in the jejunal mucosa. Immunohistochemistry localized the enzymes to the apical brush-border membrane whereas IRAP was localized in the subapical cytosolic compartment in the enterocyte. AngIV increased the glucose-induced electrogenic transport in vitro.

CONCLUSION

The present study indicates the presence of substrates and enzymes necessary for AngIV formation as well as the receptor IRAP in the jejunal mucosa. The functional data suggest that AngIV regulates glucose uptake in the healthy human small intestine.

Surgery in the treatment of type 2 diabetes mellitus

Background and Aims:

The prevalence of diabetes is increasing worldwide, and most of the cases are type 2 diabetes mellitus. The relationship between type 2 diabetes mellitus and obesity is well established, and surgical treatment is widely used for obese patients with type 2 diabetes mellitus. The aim was to present current knowledge about the possible mechanisms responsible for glucose control after surgical procedures and to review the surgical treatment results.

Material and Methods:

Medical literature was searched for the articles presenting the impact of surgical treatment on glycemic control, long-term results, and possible mechanisms of action among obese individuals with type 2 diabetes mellitus.

Results:

Remission of type 2 diabetes mellitus after bariatric surgery depends on the definition of the remission used. Complete remission rate after surgery with the new criteria is lower than was considered before. Randomized controlled studies demonstrate that surgery is superior to best medical treatment for the patients with type 2 diabetes mellitus. The recurrence of type 2 diabetes mellitus after bariatric surgery is observed in up to 40% of cases with ≥5 years of follow-up. Despite the recurrence of type 2 diabetes mellitus in this group, better glycemic control and lower risk of macrovascular complications are present. Incretin effects on glycemic control after bariatric surgery are well described, but the role of other possible mechanisms (bile acids, microbiota, intestinal gluconeogenesis) in humans is unclear.

Conclusion:

Surgery is an effective treatment of type 2 diabetes mellitus in obese patients. The most optimal surgical procedure for the treatment of obese patients with type 2 diabetes mellitus is still to be established. More research is needed to explore the mechanisms of glycemic control after bariatric surgery.

Bone mineral density and expression of vitamin D receptor-dependent calcium uptake mechanisms in the proximal small intestine after bariatric surgery

BACKGROUND

Roux-en-Y gastric bypass may lead to impaired calcium uptake. Therefore, operation-specific effects of gastric bypass and vertical banded gastroplasty on bone mineral density (BMD) were examined in a randomized clinical trial. Bone resorption markers and mechanisms of decreased calcium uptake after gastric bypass were investigated using blood and endoscopic samples from two additional patient cohorts.

METHODS

Total BMD and non-weight-bearing skull BMD were measured by dual-energy X-ray absorptiometry at baseline, and 1 and 6 years after gastric bypass or vertical banded gastroplasty in patients who were not receiving calcium supplements. Bone resorption markers in serum and calcium uptake mechanisms in jejunal mucosa biopsies were analysed after gastric bypass by proteomics including radioimmunoassay, gel electrophoresis and mass spectrometry.

RESULTS

One year after surgery, weight loss was similar after gastric bypass and vertical banded gastroplasty. There was a moderate decrease in skull BMD after gastric bypass, but not after vertical banded gastroplasty (P < 0·001). Between 1 and 6 years after gastric bypass, skull BMD and total BMD continued to decrease (P = 0·001). C-terminal telopeptide levels in serum had increased twofold by 18 months after gastric bypass. Proteomic analysis of the jejunal mucosa revealed decreased levels of heat-shock protein 90β, a co-activator of the vitamin D receptor, after gastric bypass. Despite increased vitamin D receptor levels, expression of the vitamin D receptor-regulated calcium transporter protein TRPV6 decreased.

CONCLUSION

BMD decreases independently of weight after gastric bypass. Bone loss might be attributed to impaired calcium absorption caused by decreased activation of vitamin D-dependent calcium absorption mechanisms mediated by heat-shock protein 90β and TRPV6.

Long-term results of a randomized clinical trial comparing Roux-en-Y gastric bypass with vertical banded gastroplasty

BACKGROUND

The long-term results of Roux-en-$\hbox{Y}$ gastric bypass (gastric bypass) and vertical banded gastroplasty (VBG) from randomized studies have not been described in detail.

METHODS

Patients were randomized to gastric bypass or VBG. Body mass index (BMI), body composition, eating habits and gastrointestinal hormones were reviewed after 6 years. The frequency of reoperation was assessed up to 10 years after surgery.

RESULTS

Sixty-six (80 per cent) of the 82 subjects randomized were assessed for weight and BMI 6 years after surgery, 30 (81 per cent) in the gastric bypass group and 36 (80 per cent) in the VBG group. Intention-to-treat analysis demonstrated greater weight loss after gastric bypass compared with VBG, 6 years after surgery: BMI reduced from 41·8 (95 per cent confidence interval 41·3 to 42·3) to 30·3 (28·6 to 32·0) kg/m(2) for gastric bypass and from 42·3 (42·8 to 44·8) to 32·9 (31·3 to 34·5) kg/m(2) for VBG (P = 0·036). Gastric bypass caused a larger loss of fat mass (P = 0·026) and better preservation of lean tissue (P = 0·009). Patients having a gastric bypass had greater postprandial responses to the satiety hormones glucagon-like peptide 1 and peptide YY (P = 0·003 and P = 0·004 respectively). Ghrelin levels did not differ between the groups. Patients with a gastric bypass maintained a lower intake of fat compared with those having VBG (P = 0·013). Some 89 per cent of patients who initially had VBG had undergone, or were scheduled for, conversion to gastric bypass at latest follow-up.

CONCLUSION

Gastric bypass was superior to VBG regarding weight loss, body composition, dietary composition and postprandial satiety hormone responses.

The renin-angiotensin system and the gastrointestinal mucosa

The gastrointestinal (GI) tract is fundamental for the intake of fluid and electrolytes and accommodates a large proportion of bodily hemodynamics and host defence systems. Despite that the renin-angiotensin system (RAS) is a prominent regulatory system for fluid and electrolyte homeostasis its impact on GI physiology is only little explored. Recent data indicate that RAS is well expressed and active in the GI tract although exact physiological roles are to be settled. There are several reports showing influences by RAS and its key mediator angiotensin II (AngII) on intestinal epithelial fluid and electrolyte transport and data are accumulating, suggesting involvement in GI mucosal inflammation and carcinogenesis. Of particular interest is the increasing amount of experimental support for the involvement of AngII formation and actions via the AngII subtype 1 (AT1) receptor in the pathogenesis and treatment of inflammatory bowel disease. The picture of RAS in the GI tract is, however, far from complete. Because RAS is an important application area for reno-cardiovascular diseases, a number of pharmacological agents as well as research technologies already exist and can in the future be used for GI research. A marked expansion of knowledge concerning the role of RAS in GI physiology and pathophysiology is to be expected.

Angiotensin II-induced contractions in human jejunal wall musculature in vitro

AIM

Angiotensin II is well known for its contractile effects on smooth muscle cells. This effect is also present in the gut previously shown in animal models. The aim of this study was to clarify expression and localization of angiotensin II receptors in the human small intestine and to explore the pharmacological profile of angiotensin II effects in vitro.

METHODS

Strips of jejunal muscle wall from 32 patients undergoing bariatric surgery were used to record isometric tension in vitro in response to angiotensin II (10(-10)-10(-5) M) alone and in the presence of PD123319 (10(-7) M), losartan (10(-7) M), PD123319 (10(-7) M) and losartan (10(-7) M) in combination, tetrodotoxin (TTX) (10(-6) M), atropine (10(-6) M) and guanethidine (3 x 10(-6) M). Western blot, immunohistochemistry and RT-PCR were performed on corresponding muscle samples to identify expression and localization of key components of the renin-angiotensin system.

RESULTS

Angiotensin II elicited concentration-dependent contraction in both longitudinal and circular jejunal muscle wall strips; neither TTX, atropine nor guanethidine affected this action. Losartan alone and in combination with PD123319 shifted the concentration-response curve to the right. Transcription of angiotensinogen, ACE and angiotensin II types 1 and 2 receptor RNA was detected in all patients. Immunohistochemistry detected angiotensin II type 1 receptors in the musculature; both angiotensin II types 1 and type 2 receptors were found in the myenteric plexus.

CONCLUSION

This pharmacological analysis indicates that the contractile action elicited by angiotensin II on jejunal wall musculature is primarily mediated through the angiotensin II type 1 receptor located on the musculature.

Angiotensin II induced contraction of rat and human small intestinal wall musculature in vitro

BACKGROUND

Angiotensin II (Ang II) is a well-known activator of smooth muscle in the vasculature but has been little explored with regard to intestinal wall muscular activity. This study investigates pharmacological properties of Ang II and expression of its receptors in small-intestinal smooth muscle from rats and humans.

METHODS

Isometric recordings were performed in vitro on small intestinal longitudinal muscle strips. Protein expressions of Ang II typ 1 (AT1R) and typ 2 (AT2R) receptors were assessed by Western blot.

RESULTS

Ang II elicited concentration-dependent contractions of rat jejunal and ileal muscle preparations. The concentration-response curve (rat ileum, EC(50): 1.5 +/- 0.9 x 10(-8) M) was shifted to the right by the AT1R receptor antagonist losartan (10(-7) M) but was unaffected by the AT2R antagonist PD123319 (10(-7) M) as well as by the adrenolytic guanethidine (3 x 10(-6) M) and the anticholinergic atropine (10(-6) M). Human duodenal, jejunal and ileal longitudinal muscle preparations all contracted concentration-dependently in response to Ang II. The concentration-response curve (human jejunum, EC(50): 1.5 +/- 0.8 x 10(-8) M) was shifted to the right by losartan (10(-7) M) but was unaffected by PD123319 (10(-7) M). Both AT1R and AT2R were detected in all segments of the rat small intestinal wall musculature, whereas only AT1R was readily detectable in the human samples.

CONCLUSION

Ang II elicits contractions of small-intestinal longitudinal muscle preparations from the small intestine of rats and man. The pharmacological pattern and protein expression analyses indicate mediation via the AT1R.

Duodenogastric bile reflux is common in cystic fibrosis

BACKGROUND

Patients with cystic fibrosis (CF) have a high incidence of gastroesophageal reflux disease, but few cases of mucosal injury are reported. Duodenogastric reflux has not been studied in CF but has been suggested to have a pathogenic role in producing alkaline injury to the esophageal mucosa. The aim of this study was to analyze the presence of duodenogastric reflux in patients with CF.

PATIENTS AND METHODS

Ten patients with CF and 7 healthy volunteers participated in the study. Gastroduodenal manometry and intragastric perfusion were performed in all subjects. Gastric perfusate was analyzed for bilirubin and bile acids. Only patients and controls exhibiting normal migrating motor complexes were evaluated.

RESULTS

Eight patients with CF had normal motility recordings and had significantly higher gastric bilirubin levels compared with healthy subjects (P = 0.003). The bilirubin concentration was associated with bile acid regurgitation in five patients with CF. All bile acids were conjugated with a high glycine/taurine ratio and low levels of secondary bile acids. Small amounts of keto bile acids were found in two patients.

CONCLUSION

The patients with CF had an increased incidence of duodenogastric reflux compared with healthy subjects. The bile acid composition was typical for CF with low levels of secondary bile acids. Although high bile acid concentration was found in the duodenogastric reflux in most patients with CF, the less toxic profile of the bile acids might possibly contribute to the low frequency of Barrett's esophagus in CF.

Effects of dietary nitrate on oesophageal motor function and gastro-oesophageal acid exposure in healthy volunteers and reflux patients

BACKGROUND/AIMS

High concentrations of nitric oxide (NO), derived from dietary nitrite in an acid environment, have been demonstrated in the gastric fundus and in the oesophagus. The aim of this study was to investigate whether luminal NO can influence oesophageal smooth muscle performance, lower oesophageal sphincter (LOS) function or gastric and oesophageal acid exposure.

METHODS

Eleven healthy volunteers and 9 patients with chronic gastro-oesophageal reflux disease (GORD) received a diet deprived of nitrate/nitrite but supplemented with placebo or potassium nitrate for 4 days in a randomised order. On day 4 in each trial period, manometry was performed including a sleeve sensor registration of the LOS followed by a simultaneous 24-hour intra-gastric and oesophageal pH registration.

RESULTS

Nitrate supplementation increased the proportion of effective peristalsis when analysed for the entire study population. No other significant effects of dietary nitrate were found on oesophageal motor variables, on the sphincter resting tone or on the number or duration of transient sphincter relaxations. No effect was found on either gastric acidity or gastro-oesophageal reflux variables. Major reflux symptoms were not influenced by nitrate administration.

CONCLUSION

Dietary nitrate did not significantly affect oesophageal motor or LOS function, gastro-oesophageal acid reflux or reflux symptomatology either in healthy volunteers or in GORD patients.

The angiotensin II receptor blocker candesartan improves survival and mesenteric perfusion in an acute porcine endotoxin model

BACKGROUND

Blockade of the angiotensin II type 1 (AT1) receptor has been demonstrated to ameliorate splanchnic hypoperfusion in acute experimental circulatory failure. This study focused on hemodynamic changes and survival in pigs treated with AT1 blockade prior to or during acute endotoxinemia.

METHODS

Escherichia coli lipopolysaccharide endotoxin was infused in anesthetized and mechanically ventilated pigs. Systemic, renal, mesenteric and jejunal mucosal perfusion as well as systemic oxygen and acid-base balance were monitored. The selective AT1 receptor blocker candesartan was administered prior to as well as during endotoxinemia. Control animals received the saline vehicle.

RESULTS

Pre-treatment with candesartan resulted in higher survival rate (83%, 10 out of 12 animals) compared with 50% (6 of 12) in control animals and 27% (3 of 11) in animals treated during endotoxinemia. Pre-treatment with candesartan resulted in higher cardiac output, mixed venous oxygen saturation, arterial standard base-excess, portal venous blood flow during endotoxin infusion compared with controls and animals treated during endotoxinemia. No adverse effects were found on neither systemic nor renal circulation.

CONCLUSION

The favorable results of AT1 receptor blockade prior to endotoxinemia are lost when blockade is established during endotoxinemia demonstrating the importance of the renin-angiotensin system and its dynamic involvement in acute endotoxinemic shock.

Stimulated murine macrophages as a bioassay for H. pylori-related inhibition of nitric oxide production

BACKGROUND

Interference with the L-arginine/nitric oxide pathway may be a virulence strategy for the gastric pathogen Helicobacter pylori. This study evaluates a bioassay for such inhibitory actions on nitric oxide synthase.

METHODS

Cultured murine macrophages were stimulated by lipopolysaccharide and interferon-gamma. Nitric oxide synthesis and the expression of inducible nitric oxide synthase (iNOS) at increasing concentrations of L-arginine were analysed using chemiluminescence and Western blotting, respectively.

RESULTS

The bioassay was evaluated against nitrite accumulation and two established NOS inhibitors. Bacterial extracts or whole cells of one H. pylori strain inhibited nitric oxide production at low L-arginine concentrations (2-20 microM). A higher concentration of L-arginine (200 microM) was not associated with such inhibition. The iNOS expression was not affected by any of the additives compared to stimulated controls.

CONCLUSIONS

This bioassay is a reliable and simple method for analysing iNOS inhibition, resolving effects on enzyme activity or enzyme expression. H. pylori water extract and whole cells exert an L-arginine-dependent NOS inhibition, not influencing iNOS expression.

Oesophageal intraluminal nitric oxide facilitates the acid-induced oesophago-salivary reflex

BACKGROUND

The present study explores some aspects of the triggering of the acid-induced oesophago-salivary reflex. In addition to hydrogen ions, there are two acid-dependent molecules with messenger potential in the oesophageal lumen: CO2 and NO. The aim of this study was to clarify whether oesophageal NO and CO2 participate in the regulation of salivary neutralizing capacity in response to acid exposure.

METHODS

Healthy volunteers received oesophageal acidification composed of HCl, with NO3-, or HCO3- or NO3- and HCO3- in combination. In a second series of experiments, the exposure period was divided into 2 separate 10-min events. Saliva volume and titratable buffering capacity were used to calculate alkaline secretion.

RESULTS

Salivary alkaline secretion increased markedly following 20 min intraluminal exposure to HCl. The initial part of this response was 22% +/- 2.2% larger (P < 0.05) if NO3- was present. When HCO3- was added, or if NO3- and HCO3- were given simultaneously, the secretory response tended to be lower. The accumulated responses over 70 min to 2 short HCl exposures (10 min each separated by a 30 min 'rest') compared to one long one lasting 20 min were similar regardless of the presence of NO3-.

CONCLUSION

The data suggest that oesophageal intraluminal NO facilitates initiation of the oesophago-salivary reflex. CO2 seems to have a negligible effect on alkaline salivation, and repeated stimulation does not influence the magnitude of the response over time.

Sources of intra-oesophageal nitric oxide production following intraluminal acid exposure

BACKGROUND

The aim of the present study was to assess luminal nitric oxide (NO) levels in the oesophagus during baseline and acidic conditions and to clarify the sources of such oesophageal NO formation.

METHODS

Healthy volunteers received an intra-oesophageal infusion of either HCl (100 mM) or NaCl (50 mM) on two separate study days. After a low nitrate diet, nitrate load or no dietary restrictions/pretreatment, direct intraluminal measurements of NO formation were performed using a tonometric technique. Endoscopy was performed and mucosal biopsies were taken and analysed by means of immunohistochemistry, Western blot and RT-PCR.

RESULTS

No intra-oesophageal NO was detected during baseline conditions with pH neutrality. During the infusion of HCI the NO levels rose dramatically to around 12000 ppb. This high rate of NO formation fell by 95% following deviation of saliva. NO formation after an acute nitrate load was almost doubled during acid perfusion compared to control. Immunohistochemistry demonstrated distinct staining for iNOS in the oesophageal squamous epithelial cells, and Western blot and RT-PCR confirmed the presence of iNOS.

CONCLUSION

Two sources exist for intra-oesophageal NO formation, both dependent on the luminal acidity: 1) chemical reduction of salivary nitrite, a mechanism related to dietary intake of nitrate, and 2) NO formation within the oesophageal mucosal epithelium by enzymatic degradation of L-arginine. In the latter case, the NO synthase has antigenic characteristics, indicating the inducible isoform, although a functional behaviour suggests an unconventional subtype.

Helicobacter pylori infection inhibits antral mucosal nitric oxide production in humans

BACKGROUND

Inducible NO synthase expression is upregulated in H. pylori-infected gastric mucosa, suggesting increased NO synthesis as part of a host defense reaction. This study investigates actual NO production in the human antrum in situ.

METHODS

Gastroscopy with antral biopsy sampling and intragastric tonometric NO assessments were performed on H. pylori-positive and -negative volunteers. The antral mucosal specimens were analyzed with regard to inducible NO synthase (Western blotting) and the presence of the endogenous NO synthase inhibitor asymmetric dimethylarginine (ADMA) as well as L-arginine.

RESULTS

Mucosal expression of inducible NO synthase was markedly increased in H. pylori infected subjects compared to noninfected ones. The ratio between the tissue contents of L-arginine and asymmetric dimethylarginine was considerably lower in the infected group. Antral output of NO was similar in the two groups during baseline conditions. Following intragastric L-arginine exposure. the antral NO production in controls was unaltered (from 442 ppb +/- 104 to 286 ppb +/- 94), whereas it increased (from 524 ppb +/- 162 to 1066 ppb +/- 274) in the infected individuals.

CONCLUSIONS

The study confirms that NO synthase expression is increased in H. pylori-infected antral mucosa. However, NO synthesis is restricted owing to the presence of pathogen-induced competitive NO synthase inhibitors such as methylated arginines.

Jejunal luminal nitric oxide during severe hypovolemia and sepsis in anesthetized pigs

OBJECTIVE

Lowered gut blood perfusion and the associated intestinal mucosal barrier dysfunction is considered important in the pathophysiology leading to critical illness. Intestinal mucosal nitric oxide formation has been attributed a key role in the regulation of epithelial permeability and other properties of the intestinal mucosal barrier. This study was performed to delineate intestinal mucosal NO formation during hypovolemia or sepsis, both of which are associated with intestinal hypoperfusion.

MATERIALS AND METHODS

Seventeen pigs were subjected to 2 h of severe hypovolemia (bleeding induced) or sepsis (systemic infusion of live Escherichia coli) or no treatment (controls). Jejunal mucosal NO production was monitored by a tonometer. Mesenteric blood flow was measured as portal venous blood flow by an ultrasonic transit time flowmeter probe, and oxygen delivery and consumption were calculated from regional blood samples.

RESULTS

Intestinal perfusion and oxygen delivery were reduced by the same order of magnitude in both groups. Jejunal mucosal NO production and oxygen consumption decreased markedly in the hypovolemia group but remained stable in the group subjected to septic shock.

CONCLUSIONS

These data suggest that blood loss inhibits jejunal mucosal NO production as part of a general downregulation of nonvital organs. Sepsis represents a more complex stress condition with activation/maintenance of host defense mechanisms as reflected by maintained jejunal mucosal NO production despite reduced gut blood perfusion.

Dynamic involvement of the inducible type of nitric oxide synthase in acid-induced duodenal mucosal alkaline secretion in the rat

It has previously been shown that mucosal nitric oxide synthase (NOS) is involved in acid-induced duodenal mucosal alkaline secretion. The primary aim of the present study was to elucidate which isoform of NOS is responsible in rats. Immunohistochemistry showed that inducible NOS (iNOS) was constitutively expressed in villous epithelial cells. Exposing the duodenal mucosa to 10 mM HCl resulted in an increased duodenal mucosal alkaline secretion. This response was totally inhibited by intraluminal administration of a selective inhibitor of iNOS (L-N6-1-iminoethyl-lysine). One hour after the acid exposure, western blot technique showed a marked increase in mucosal iNOS expression. A second acid exposure resulted in a further stimulation of alkaline secretion. These data suggest that exposure of the duodenal mucosa to HCI initiates an increased mucosal alkaline secretion, via NO synthesis mediated by iNOS located in the epithelial cells of the villi. In addition, luminal acid stimulates expression of iNOS.

Gastric IgA in cystic fibrosis in relation to the migrating motor complex

BACKGROUND

Gastrointestinal symptoms in cystic fibrosis are frequent, but little is known about the underlying pathophysiology. Mucosal secretion of IgA is important for the immunologic function in the human gastrointestinal tract but has not been studied in cystic fibrosis. The aim of this study was to quantify the release of IgA by the gastric mucosa in relation to interdigestive motor activity in patients with cystic fibrosis with different genotypes.

METHODS

The study included 7 healthy adult volunteers and 10 adult patients with cystic fibrosis, all Helicobacter pylori-negative. All patients had pathological sweat tests and clinical symptoms and signs of cystic fibrosis. All but one were colonized with Pseudomonas aeruginosa. Three patients were pancreatic sufficient. The investigation was performed using intragastric perfusion and gastroduodenal manometry.

RESULTS

During the investigation, 8 of 10 patients with cystic fibrosis showed the characteristic pattern of interdigestive motility. The patients had significantly lower levels of gastric IgA compared to healthy subjects during phases II and III of migrating motor complex, median (range) 120 (67-442) and 36 (6-299) microg/5 min. 382 (40-1176) and 56 (4-398) (P = 0.03 and P = 0.04), respectively. Only one patient with genotype R668C/unknown showed IgA levels within the normal range. There was no correlation to gastric presence of duodenogastric reflux markers.

CONCLUSION

The interdigestive motility pattern was normal in most patients with cystic fibrosis. The low levels of IgA released from the gastric mucosa in the patients might indicate a defective gastric transmucosal IgA transport in cystic fibrosis.

Angiotensin II type 2 receptor-mediated duodenal mucosal alkaline secretion in the rat

The aims of this study were to elucidate the distribution of angiotensin receptors (AT(1) and AT(2)) in the duodenal wall and to investigate whether AT(2) receptors are involved in the regulation of duodenal mucosal alkaline secretion, which is of importance for the mucosal defense against gastric acid. Immunohistochemistry was used to locate AT(1) and AT(2) receptors in chloralose-anesthetized rats. Duodenal mucosal alkaline output was measured by use of in situ pH-stat titration. Immunohistochemistry demonstrated a distinct staining for both AT(1) and AT(2) receptors in the lamina propria of the villi and also for AT(1) receptors in the muscularis interna. When angiotensin II was infused in the presence of the AT(1) receptor antagonist losartan, mucosal alkaline secretion increased by ~50%. This response was inhibited by the AT(2) receptor antagonist PD-123319. The AT(2) receptor agonist CGP-42112A increased mucosal alkaline secretion by ~50%. This increase was absent in the presence of PD-123319 but not in the presence of losartan or the local anesthetic lidocaine. We conclude that angiotensin II stimulates duodenal mucosal alkaline secretion by activation of AT(2) receptors located in the duodenal mucosa/submucosa.

Effects of hypovolaemia on acid-induced duodenal mucosal damage in the rat

Modest acute hypovolaemia in rats markedly decreases the duodenal mucosal alkaline secretion via neurohumoral links. The present study was undertaken to investigate if such a procedure influences the morphological changes observed following an acid challenge of the duodenal mucosa. Experiments were performed on anaesthetized male Sprague-Dawley rats. HCl (10 or 100 mM) was infused during 15 min into the duodenum via a luminally situated catheter. Time controls were compared with animals bled 10% of total blood volume. Mucosal damage was evaluated by light microscopic morphometry on transverse sections and by scanning electron microscopy of the luminal surface. Perfusion with either 10 mM or 100 mM HCl reduced villus length by about 30%. The villus area was unaffected by 10 mM HCl, but was reduced significantly by 10% by 100 mM HCl as compared with NaCl time controls. Hypovolaemia did not influence the morphometrical changes induced by 10 mM HCl but reduced significantly both villus length (-28%) and villus area (-10%) as compared with the unbled 100 mM HCl group. Scanning electrone microscopy (SEM)-based visual damage score was not influenced by the hypovolaemia procedure in any of the acidities. Morphological changes of the duodenal mucosa, induced by moderate intra-luminal acidity (10 mM HCl), is not influenced by hypovolaemia. However, at higher acidities (100 mM HCl) the hypovolaemia contributes to more severe mucosal damage.

Intragastric nitric oxide/nitrite in Helicobacter pylori-infected subjects

BACKGROUND

Nitrite (NO2-) in swallowed saliva is reduced to nitric oxide (NO) and other nitrogen oxides by the intragastric acidity. This mechanism is probably important for the intragastric clearance of ingested micro-organisms and nitrosating compounds. The study examines the balance between intragastric NO and NO2- in relation to endogenous acid production and infection with Helicobacter pylori.

METHODS

Six healthy H. pylori-negative and six H. pylori-positive volunteers with no known gastroduodenal pathology were examined after an overnight fast. Gastric NO was measured using a chemiluminescence technique and pH as well as NO2- were analysed in gastric aspirates.

RESULTS

Gastric NO was slightly lower in H. pylori-positive subjects (1560 +/- 211 ppb) than in uninfected controls (2112 +/- 430 ppb; P > 0.05) during basal conditions, whereas both pH and NO2- concentration were similar in the two groups. During inhibition of acid secretion (omeprazole 20 mg b.i.d. over 5 days) median pH and mean NO2- concentration in gastric aspirates were significantly higher in H. pylori positives than in the controls. Furthermore, during omeprazole treatment the intragastric NO levels were almost absent in H. pylori positives, whereas approximately 50% remained in H. pylori-negative individuals.

CONCLUSION

Proton-pump inhibition in H. pylori-infected individuals abolishes the intragastric chemical reduction of swallowed NO2- in the fasting stomach.

Gastric secretion in cystic fibrosis in relation to the migrating motor complex

BACKGROUND

Patients with cystic fibrosis (CF) have been claimed to have defect intestinal motility and gastric acid secretion. The aim of this work was to study the interdigestive motility and the motility-related secretions in the upper gastrointestinal tract in patients with CF compared to healthy controls.

METHODS

Concomitant gastroduodenal manometry combined with intragastric perfusion was performed in 12 healthy volunteers and 10 patients with CF.

RESULTS

Eight CF patients showed a normal migrating motor complex. Motility-related gastric secretion of acid and bicarbonate was evaluated in six patients and did not differ from healthy subjects. Gastric net fluid secretion was significantly decreased in the CF patients and bilirubin reflux was significantly increased. The CF patients with pancreatic insufficiency lacked motility-related variations in plasma levels of motilin and pancreatic peptide.

CONCLUSIONS

No defect in fasting motility or gastric secretion of acid or bicarbonate could be seen in well-nourished adult CF patients. The main finding was a significantly lower net fluid secretion and higher bilirubin reflux compared to healthy subjects. Indications of a genetic relationship could be seen.

[When is H pylori a cause of duoenal ulcer? Hypersecretion of gastric acid, active duodenitis and reduced bicarbonate secretion are links in the chain]

Helicobacter pylori infection engaging mainly the gastric antrum causes hypersecretion of gastric acid. The increased duodenal acid load gives rise to islands of gastric mucosa in the proximal duodenum. As these bacteria thrive only on gastric mucosa it presents an opportunity for Helicobacter pylori to colonize the duodenum. A much higher density of virulent Helicobacter pylori has been found in the duodenum of duodenal ulcer patients in comparison to infected subjects without duodenal ulcer. The high density of virulent Helicobacter pylori in the proximal duodenum results in a strong inflammatory reaction with active duodenitis and impaired bicarbonate secretion. These characteristics of duodenal ulcer patients, together with the acid hypersecretion, seem to be the key factors in evoking a duodenal ulcer.

Intragastric CO2 and nitric oxide participate in the regulation of peptone-induced gastrin release in humans

BACKGROUND

Moderate acidification of the gastric lumen inhibits peptone-induced gastrin release. The aim of the present study was to investigate if the gastric acid neutralization products CO2 (from secreted HCO3) and NO (from reduced salivary nitrite) could act as intermediate messengers between luminal acidity and the inhibition of peptone-induced gastrin release.

METHODS

Fourteen healthy volunteers (mean age, 27 years; range, 20-39 years; 3 women) participated in the study. Intragastric perfusion with saline or peptone was performed on the healthy volunteers. Venous blood samples were analyzed for serum gastrin concentrations. Intragastric NO was measured by chemiluminescence.

RESULTS

Basal serum gastrin ranged between 11 and 23 pmol/l. Peptone in Sörensen's phosphated buffer (pH 6.9, PCO2 0 mmHg) increased serum gastrin by 83% +/- 23%, whereas acidified peptone (pH 2.0) did not stimulate gastrin release. Acidified peptone buffered with NaHCO3 to neutrality (pH 6.9, PCO2 approximately 600 mmHg) increased serum gastrin by 166% +/- 29%. Low intragastric NO levels were obtained by deviation of saliva. During such salivary depletion, acidified peptone (pH 2.0) stimulated gastrin release to a level of about 40% of the control response (pH 6.9). This peptone-induced gastrin response during salivary deviation was inhibited by addition of nitrite to the perfusate.

CONCLUSIONS

Acid-induced inhibition of peptone-stimulated gastrin release is partly dependent on intraluminal NO formed in the reaction between salivary nitrite and gastric acid. In addition, the gastric acid neutralization product CO2 seems to potentiate the effect of peptone on gastrin release.

Angiotensin II blockade in existing hypovolemia: effects of candesartan in the porcine splanchnic and renal circulation

Angiotensin II (AngII) is an important vasoconstrictor during hypovolemia. This study focused on the effects of the AngII receptor blocker candesartan on intestinal, hepatic, and renal hemodynamics during severe hypovolemia when administered in preexisting moderate hypovolemia. It was hypothesized that specific AngII receptor blockade might enhance splanchnic perfusion during hypovolemia. Fasted, anesthetized, ventilated, juvenile pigs were hemorrhaged by 20% of the blood volume for 30 min. Animals were then randomized to receive candesartan (CAND, n = 11) or the vehicle (CTRL, n = 10) prior to further hemorrhage to 40% of the blood volume for 30 min. The shed blood was then retransfused. Systemic and splanchnic hemodynamics were recorded including intestinal mucosal, superficial and parenchymal hepatic, and cortical and medullary renal microcirculation by laser-Doppler flowmetry. Arterial blood gases were analysed. Candesartan-treated animals maintained mesenteric and jejunal mucosal perfusion during 40% hypovolemia compared to CTRL animals, while no differences were observed in the hepatic and renal circulation. Retransfusion restored mesenteric and renal blood flows despite persistent hypotension and reduced cardiac output in both CAND and CTRL animals. Renal medullary and hepatic parenchymal microcirculation failed to recover during retransfusion in both CAND and CTRL animals. Arterial acidosis, hypercarbia, and a negative base excess were observed in CTRL animals following retransfusion whereas those parameters were normalised in CAND animals. Administration of candesartan in moderate hypovolemia ameliorated the reduction and consequences of mesenteric and intestinal, but not hepatic perfusion during severe hypovolemia. No adverse effects were observed in the renal circulation.

Jejunal mucosal nitric oxide production and substrate dependency during acute mesenteric hypoperfusion in pigs

OBJECTIVE

Jejunal nitric oxide (NO) formation is impaired during mucosal hypoperfusion. This study was undertaken to investigate whether this phenomenon could result from a restricted mucosal availability of NO-synthase substrates, ie, oxygen and/or L-arginine.

DESIGN

Controlled study using laboratory animals.

SETTING

University animal research laboratory.

SUBJECTS

Eighteen chloralose-anesthetized, ventilated, juvenile Landrace domestic pigs.

INTERVENTIONS

Mesenteric hypoperfusion was induced by intrapericardial infusion of Ringer's solution to achieve decreased cardiac output by creation of cardiac tamponade.

MEASUREMENTS AND MAIN RESULTS

Animals were prepared for jejunal intraluminal perfusion with 150 mM NaCl or 3 mM L-arginine solution in an isolated intestinal segment and then subjected to cardiac tamponade. Jejunal mucosal NO formation was measured with a tonometric technique. Mesenteric blood flow was measured as portal blood flow, and mucosal perfusion was measured by laser Doppler flowmetry. Regional oxygen consumption and delivery were calculated from arterial and portal blood samples. Cardiac tamponade reduced jejunal NO formation (-52%), mesenteric oxygen delivery (-75%), oxygen consumption (-39%), and mucosal perfusion (-43%). Oxygenation of the jejunal intraluminal perfusate completely restored the intestinal NO levels within 30 mins, whereas presence of L-arginine was without effect.

CONCLUSIONS

The study indicates that oxygen rather than L-arginine is the rate-limiting factor for mucosal NO production during acute reduced splanchnic perfusion.

Tonometric assessment of jejunal mucosal nitric oxide formation in anaesthetized pigs

Nitric oxide (NO) in the gut has attracted increasing interest as a regulatory factor for a wide variety of intestinal functions. This study was performed to evaluate some methodological aspects and jejunal sources for NO synthesis. Bench side evaluations and an animal model using chloralose-anaesthetized pigs were used. Immunohistochemistry was performed on samples from pig intestine and direct measurements of intestinal NO formation were performed using intraluminal tonometry. Tonometric measurements were quantitatively accurate and with high reproducibility. A substantial NO formation was assessed which was markedly inhibited by luminal administration of the non-selective NOS inhibitor L-NAME. Intravenous administration of L-NAME also reduced jejunal NO formation but to a lesser extent. Immunohistochemistry revealed staining for the inducible type of NOS in the mucosal surface epithelium whereas endothelial and neuronal subtypes were located in deeper layers of the jejunal wall. The study argues for that the source of jejunal NO production, as measured by intraluminal tonometry, is located in close proximity with the intestinal mucosa. The NOS in this compartment is predominantly of the inducible type.

Specific angiotensin II receptor blockage improves intestinal perfusion during graded hypovolemia in pigs

OBJECTIVE

To investigate the potential of specific angiotensin II subtype 1 (AT1) receptor blockade to modify the mesenteric hemodynamic response to acute hypovolemia and retransfusion.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University-affiliated animal research laboratory.

SUBJECTS

Fasted, anesthetized, ventilated, juvenile domestic pigs of both sexes.

INTERVENTIONS

Acute, graded hypovolemia by 20% and 40% of the total estimated blood volume followed by retransfusion in control animals (CTRL; n = 10) and animals pretreated with the AT1 receptor blocker candesartan (CAND; n = 10).

MEASUREMENTS AND MAIN RESULTS

Invasive monitoring of arterial and central venous blood pressures, cardiac output, portal venous blood flow, and jejunal mucosal blood flow. Blood gases were repeatedly analyzed to calculate oxygen delivery and consumption. Thirty minutes after each level of hypovolemia at 20% and 40%, cardiac output was decreased in CTRL animals from a baseline of 2.9 +/- 0.1 to 1.8 +/- 0.2 and 1.1 +/- 0.2 L/min, with no differences compared with CAND animals. Cardiac output was restored to 3.0 +/- 0.3 L/min 30 mins after retransfusion in CTRL animals, with no significant intergroup differences. Baseline portal venous blood flow (Q(MES)) and jejunal mucosal perfusion (PU(JEJ)) were greater in CAND animals compared with CTRL animals. During graded hypovolemia, CAND animals maintained Q(MES) and PU(JEJ) at significantly higher levels compared with CTRL animals, particularly after 40% hemorrhage (+221% and + 244%, respectively, relative to the mean values in CTRL animals). The same pattern was observed after retransfusion. Moreover, the calculated mesenteric critical oxygen delivery was significantly greater in CTRL animals (74 mL/min) compared with CAND animals (34 mL/min). No animals died in the CAND group, whereas four animals died during 40% hypovolemia or retransfusion in the CTRL group.

CONCLUSIONS

Specific AT1 blockade before acute hypovolemia significantly ameliorated mesenteric and, in particular, jejunal mucosal hypoperfusion. In addition, cardiovascular stability was improved, and mortality in conjunction with acute hypovolemia and retransfusion could be completely avoided. These findings support a fundamental role of the renin-angiotensin system in the mesenteric response to acute hypovolemia and indicate a substantial interventional potential for candesartan in conjunction with circulatory stress.

Conceivable mechanisms by which Helicobacter pylori provokes duodenal ulcer disease

A conceivable concept for the development of duodenal ulcers in Helicobacter pylori (H. pylori) infected subjects is presented in this chapter. The concept includes an explanation of the fact that only a minority of all H. pylori-infected subjects will develop a duodenal ulcer. Helicobacter pylori infection of the antrum induces a hypersecretion of gastric acid secretion, giving rise to gastric metaplasia in the duodenal bulb. This gastric metaplasia is a prerequisite for H. pylori colonization of the bulb. These events are common to all H. pylori-infected subjects. However, a much higher density of H. pylori bacteria and colonization with virulent organisms has been found in the bulb of duodenal ulcer patients, resulting in a much stronger inflammatory reaction with active duodenitis and an impaired bicarbonate secretion. These characteristics, together with acid hypersecretion, seem to be the important factors in evoking a duodenal ulcer.

Differentiation of the peptidergic vasoregulatory response to standardized splanchnic hypoperfusion by acute hypovolaemia or sepsis in anaesthetized pigs

This study was performed to integratively investigate the vasoregulatory response during standardized splanchnic hypoperfusion in pigs. Splanchnic perfusion was reduced to 50% of baseline by: haemorrhage by 20 and 40% of the estimated total blood volume; femoral venous infusion of live E. coli to establish sepsis of systemic origin; portal venous infusion of live E. coli to establish sepsis of splanchnic origin. Invasive haemodynamic monitoring and radioimmunoassay analyses of arterial plasma concentrations of angiotensin II, endothelin-1 and atrial natriuretic peptide were carried out. Acute hypovolaemia reduced systemic and splanchnic vascular resistances following transient increases and increased angiotensin II levels (+587%), whereas endothelin-1 and atrial natriuretic peptide levels did not change significantly. Systemic sepsis following femoral venous infusion of E. coli resulted in increased splanchnic vascular resistance and increased levels of angiotensin II (+274%), endothelin-1 (+134%) and atrial natriuretic peptide (+185%). Infusion of E. coli via the portal venous route induced an increase in splanchnic vascular resistance associated with particularly elevated levels of angiotensin II (+1770%) as well as increased endothelin-1 (+201%) and atrial natriuretic peptide (+229%) concentrations. Hypovolaemia and sepsis, although standardized with a predefined level of splanchnic hypoperfusion, elicited differentiated cardiovascular and vasopeptidergic responses. Sepsis, particularly of portal origin, notably increased splanchnic vascular resistance related to increased production of the vasoconstrictors angiotensin II and endothelin-1. The role of atrial natriuretic peptide as a vasodilator seems to be of subordinate importance in hypovolaemia and sepsis.

Splanchnic circulation and regional sympathetic outflow during peroperative PEEP ventilation in humans

The splanchnic organs represent a major target for sympathetic outflow and an important region for haemodynamic effects on cardiovascular homeostasis. We have studied regional haemodynamic and sympathetic changes in the splanchnic bed during standardized circulatory stress from positive end-expiratory pressure ventilation (PEEP). We investigated eight patients undergoing major upper abdominal surgery using a radiotracer method to measure plasma spillover of norepinephrine as an index of sympathetic nerve activity using arterial, portal and hepatic venous blood sampling. Mesenteric and hepatic perfusion were measured by ultrasound transit time flowmetry and blood-gas analyses. Steady state measurements were performed before and during PEEP ventilation at 10 cm H2O. Plasma spillover of norepinephrine in the mesenteric and hepatic organs represented mean 49 (SEM 8)% and 7 (2)%, respectively, of systemic norepinephrine spillover at baseline, and PEEP ventilation did not cause any significant changes. However, PEEP ventilation significantly decreased portal venous blood flow while hepatic blood flow was preserved by a compensatory increase in hepatic arterial blood flow. Mesenteric and hepatic oxygen delivery changed according to blood flow, and there were no changes in regional oxygen consumption. Thus PEEP ventilation altered mesenteric and hepatic perfusion, independent of any change in corresponding sympathetic nerve activity. Regulation of hepatic blood supply, not related to sympathetic activity, maintained liver oxygenation during PEEP ventilation despite a simultaneous decrease in mesenteric perfusion.

Is the esophageal squamous epithelial barrier function impaired in patients with gastroesophageal reflux disease?

BACKGROUND

A disturbed epithelial barrier function has been promoted as one factor in the pathogenesis of gastroesophageal reflux disease (GERD). We therefore studied the effect of acid perfusion on the transmural potential difference (PD) of the distal esophagus in relation to onset of reflux symptoms.

METHODS

PD was assessed during perfusion with saline and with 0.1 M HCl in healthy controls (n = 17) and in GERD patients without (n = 15) or with esophagitis (n = 6) and in remission after a fundoplication (n = 10). Heartburn and other upper GI symptoms were recorded concomitantly. Endoscopy-negative patients were studied before and after omeprazole treatment.

RESULTS

HCl perfusion induced more lumennegative peak PD values in patients with active GERD, regardless of the presence or absence of esophagitis, than in healthy controls. After successful therapy, the PD response to acid perfusion equalled that of healthy subjects. Acid perfusion was associated with the onset of heartburn in most patients with active GERD but in none of the healthy subjects, and less frequently after medical and surgical therapy.

CONCLUSIONS

The epithelial permeability to hydrogen ions differs between healthy subjects and patients with active GERD. Effective treatment, such as omeprazole or fundoplication, might improve the barrier function.

Carbon dioxide mediates duodenal mucosal alkaline secretion in response to luminal acidity in the anesthetized rat

BACKGROUND & AIMS

Acid exposure of the duodenum elicits various functional responses, e.g., an increased mucosal alkaline secretion. Despite low pH in luminal contents, the mucosal secretion of bicarbonate-rich fluid results in pH neutrality at the surface epithelium. It follows that it is probably not luminal pH that triggers the secretory response. The present study was undertaken to investigate if CO2 could serve as an intermediate messenger between luminal acid and the mucosal secretory response.

METHODS

Experiments were performed on chloralose-anesthetized rats. The duodenal mucosal alkaline secretion was measured by in situ pH-stat titration.

RESULTS

Exposure of the duodenal mucosa to CO2, administered either as a pregassed solution (pH 4, PCO2 700 mm Hg) or as an acidified bicarbonate solution (pH 6.4, PCO2 240 mm Hg), raised the alkaline output by approximately 65%. This response was blocked by the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (0.3 mmol/L intraluminally) but not by indomethacin (5 mg/kg intravenously).

CONCLUSIONS

Exposure of the duodenal mucosa to solutions with high concentrations of CO2 increases the mucosal alkaline secretion despite an almost neutral pH. Data indicate that the L-arginine/NO pathway is involved in the mediation of this response.

Human duodenogastric reflux, retroperistalsis, and MMC

The aim of this study was to determine to what extent human migrating motor complex (MMC)-related secretory phenomena are influenced by a recently discovered period of duodenal retroperistalsis during late phase III. A constant-flow perfusion technique was used to measure gastric appearance of acid, bicarbonate, pepsin, bilirubin, IgA, and duodenally infused [14C]polyethylene glycol (PEG) 4000 in 12 healthy volunteers. Interdigestive gastroduodenal motility was recorded by digital manometry. During late antral phase II and III, the gastric lumen was acidified (P < 0.005 phase III vs. phase I) together with a marked increase in luminal pepsin output (3.1 +/- 1.2 during phase III vs. 0.25 +/- 0.08 kU/5 min in phase I, P < 0.01), followed by a realkalinization due to a simultaneous reduction of acid secretion and a duodenogastric reflux, aided by retrograde peristalsis, of bicarbonate and IgA but not of bilirubin, at the end of antral phase III (P < 0.05 phase III vs. phase I values). This physiological duodenoantral reflux phenomenon may play an important role in the chemical and immunological restitution of the antral mucosal barrier function after the exposure to high acid and pepsin concentrations during antral phase III activity.

Detecting gastrointestinal hypoperfusion during cardiac tamponade in pigs: a role for nitric oxide tonometry?

OBJECTIVE

To evaluate different techniques and regional approaches for detecting critical reductions in gastrointestinal (GI) perfusion.

DESIGN

Laboratory, animal, controlled study.

SETTING

University animal research laboratory.

SUBJECTS

Thirteen anesthetized, ventilated, juvenile domestic pigs.

INTERVENTIONS

Dextran was infused into the pericardial sac to achieve cardiac tamponade that reduced cardiac output to 25% of baseline value. Hemodynamics were invasively monitored, and blood gases were sampled in the systemic and portal circulations. Tonometers were placed in the corpus of the stomach and in the jejunum, 50 cm aboral to the ligament of Treitz.

MEASUREMENTS AND MAIN RESULTS

We measured cardiac output, portal venous blood flow, mesenteric oxygen delivery and consumption, systemic and portal venous blood gases and acid-base balance, stomach and jejunal transepithelial potential difference, stomach and jejunal intramucosal pH, arterial plasma concentrations of asymmetric dimethylarginine, and jejunal, intraluminal nitric oxide. One hour of cardiac tamponade decreased mesenteric oxygen delivery and consumption in a linear fashion and resulted in mesenteric acidosis, as evidenced by decreases in pH, standard bicarbonate, oxygen saturation, and PO2 and increases in PCO2. The potential difference in the jejunum decreased earlier than in the stomach, whereas stomach intramucosal pH decreased before jejunal intramucosal pH. Intraluminal nitric oxide in the jejunum was markedly reduced soon after cardiac tamponade. This reduction was accompanied by an increase in arterial plasma concentrations of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine. Investigated variables were unchanged in control animals.

CONCLUSIONS

Both intramucosal pH and potential difference measurements may be used to detect critical reduction in GI perfusion. Regional and temporal differences may reduce the accuracy of these methods. Jejunal tonometry can yield an early nitric oxide measurement that indicates mesenteric low-flow conditions. Jejunal tonometry also yields quantitative information about this modulator of hemodynamic and mucosal barrier function, information that is relevant to GI failure during shock.

Acid-induced duodenal mucosal nitric oxide output parallels bicarbonate secretion in the anaesthetized pig

We recently showed the involvement of the L-arginine/nitric oxide (NO) pathway in acid-induced duodenal mucosal bicarbonate secretion in rats. The aim of the present study was to confirm this observation in pigs by direct measurements of NO production. Experiments were performed on 16 anaesthetized pigs of both sexes treated with guanethidine (6 mg kg-1, intravenously). A duodenal segment, devoid of pancreaticobiliary influxes, was perfused with saline and the duodenal mucosal bicarbonate secretion was calculated from continuous measurements of pH and PCO2. The perfusate contents of NO and its oxidative product nitrite were determined by chemiluminescence, after reduction of nitrite to NO. Luminal acidification with 30 mM hydrochloric acid increased the output of bicarbonate as well as NO to the perfusate, by 195 +/- 45% and 106 +/- 10%, respectively. These responses to acid were markedly inhibited by adding the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 0.3 mM) to the perfusate. The inhibitory effect of L-NMMA could be reversed by administration of L-arginine (3 mM). The study presents simultaneous measurements of bicarbonate and NO outputs to a duodenal luminal perfusate. The results strongly support the view that the L-arginine/NO pathway is involved in the acid-induced duodenal mucosal bicarbonate secretory response.

Acid-induced increase in duodenal mucosal alkaline secretion in the rat involves the L-arginine/NO pathway

Duodenal mucosal alkaline secretion increases in response to hydrochloric acid exposure. The tentative role of nitric oxide (NO) in the mediation of this response was investigated. The mucosal alkaline output by a duodenal segment was recorded by in situ titration in chloralose-anaesthetized rats. In some experiments the duodenal blood flow was estimated by laser-Doppler flowmetry. Exposure of the duodenum to acid (0.01 M HCl, 5 min) increased the alkaline secretion by approximately 85%. The NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10 mg kg-1 intravenously or 0.3 mM intraluminally) blocked the secretory increment after mucosal acid exposure. Mean arterial pressure and basal alkaline secretion were markedly raised, whereas duodenal blood flow was decreased, when L-NAME was given intravenously (i.v.). Intraluminal (i.l.) administration left mean arterial pressure as well as duodenal blood flow unaltered, and the duodenal mucosal alkaline secretion was only slightly elevated. The stereoisomer NG-nitro-D-arginine methyl ester (D-NAME) had no effect on either basal or acid-induced duodenal alkaline output. In animals receiving L-arginine (10 mg kg-1 min-1 i.v., or 3 mM i.l.) and L-NAME, the acid exposure elicited an increase in duodenal mucosal alkaline secretion, similar to that observed in controls. The results suggest that the acid-induced increase in duodenal mucosal alkaline secretion involves NO synthesis, which takes place close to the lumen, probably within the mucosa.

Water extract of Helicobacter pylori inhibits duodenal mucosal alkaline secretion in anesthetized rats

BACKGROUND & AIMS

The pathophysiology behind Helicobacter pylori-induced gastroduodenal dysfunction is incompletely understood. The aim of this study was to investigate if a water extract of H. pylori distorts acid-induced duodenal mucosal alkaline secretion.

METHODS

Chloralose-anesthetized rats were prepared for duodenal luminal perfusion and in situ pH-stat titration of mucosal alkaline secretion.

RESULTS

Mucosal bicarbonate secretion increased approximately 55%-60% after a 5-minute exposure to 10 mmol/L HCl. This response was absent when water extracts of three strains of H. pylori (protein content, 0.2-20 microg/mL) had been added to the perfusate. Presence of 3 mmol/L L-arginine, but not the stereoisomer D-arginine, in the luminal perfusate reversed the H. pylori extract blockade of acid-induced mucosal alkaline secretion. High-performance liquid chromatography-based analyses showed that the endogenous nitric oxide synthase inhibitor asymmetric dimethyl arginine (ADMA) increased fourfold in duodenal perfusate and fivefold in duodenal tissue after H. pylori extract exposure. In vitro proteolysis of H. pylori extract also resulted in a substantial accumulation of ADMA. Exogenously administered ADMA, giving similar tissue concentrations, inhibited the mucosal alkaline response to acid exposure.

CONCLUSIONS

Water extracts of H. pylori inhibit acid-induced mucosal alkaline secretion via interference with mucosal NO synthase.

Sympathetic and renin-angiotensin activation during graded hypovolemia in pigs: impact on mesenteric perfusion and duodenal mucosal function

Sympathetic and angiotensinergic activation reduce splanchnic oxygen delivery during hypovolemia, which may lead to failure of the intestinal mucosal barrier and eventually multiple organ dysfunction. This study integrates sympathetic and angiotensinergic responses with splanchnic hemodynamics and duodenal mucosal function during hypovolemia and evaluates pharmacologic blockade of either system to ameliorate the impact of acute hypovolemia. Chloralose-anesthetized pigs subjected to 20 and 40% blood volume reductions were randomized to controls or administered guanethidine or enalaprilate to block sympathetic and angiotensinergic activation, as assessed by plasma norepinephrine spillover and angiotensin II levels, respectively. Mesenteric and hepatic oxygen delivery/consumption as well as duodenal mucosal alkaline secretion and potential difference were determined. Hypovolemia preferentially increased mesenteric sympathetic outflow and caused a vigorous angiotensinergic activation. Guanethidine and enalaprilate blocked effectively the sympathetic and angiotensinergic responses. Treatment with enalaprilate, but not guanethidine, prevented the reduction of mesenteric oxygenation and duodenal mucosal alkaline secretion and potential difference observed in control animals. The down-regulation of mesenteric oxygenation and duodenal mucosal function during hypovolemia can be prevented by administration of enalaprilate, whereas guanethidine is uneffective in this respect. Interference with the reninangiotensin system might be of clinical interest to support mesenteric perfusion and organ function in hypovolemia.

ACE inhibition by enalaprilate stimulates duodenal mucosal alkaline secretion via a bradykinin pathway in the rat

The effects of enalaprilate on duodenal mucosal alkaline secretion (in situ titration) and mean arterial blood pressure were investigated in chloralose-anesthetized male rats. A bolus injection of enalaprilate (0.7 mg/kg intravenously) increased alkaline secretion by about 60%, and this response was resistant to guanethidine (5 mg/kg intravenously), splanchnicotomy, and vagotomy. Furthermore, angiotensin II infusion (0.25-2.5 microg/kg/hr intravenously) following the administration of enalaprilate failed to influence this response. Bradykinin (10(-6)-10(-4) M) applied topically to the serosal surface of the duodenal segment under study increased dose-dependently the duodenal mucosal alkaline secretion, an effect that could be blocked by the selective bradykinin receptor subtype-2 antagonist HOE140 (100 nmol/kg intravenously). HOE140 also antagonized the response to enalaprilate. These data suggest that enalaprilate increases duodenal mucosal alkaline secretion via a local bradykinin pathway involving receptors of the bradykinin receptor subtype-2 antagonist, rather than by blockade of endogenous angiotensin II or by central autonomic neural regulation.

ANG II prolongs splanchnic nerve-mediated inhibition of duodenal mucosal alkaline secretion in the rat

Hypovolemia inhibits duodenal mucosal alkaline (HCO-3) secretion by activation of sympathoadrenergic nerves. A possible involvement of the renin-angiotensin system was investigated. Experiments were performed on chloralose-anesthetized rats. The mucosal alkaline output by a duodenal segment was measured using in situ pH-stat titration equipment. A modest hypovolemia was induced by bleeding the animals approximately 10% of the total blood volume. This procedure decreased duodenal mucosal alkaline secretion to a sustained level of approximately 50% of baseline and reduced mean arterial pressure by approximately 20 mmHg. Intravenous pretreatment with the angiotensin-converting enzyme (ACE) inhibitor enalaprilate (0.7 mg/kg) or the angiotensin II-receptor antagonist losartan (10 mg/kg) altered the response to hypovolemia to a transient one, and alkaline secretion returned to the control level within 40-50 min. When exogenous angiotensin II was administered intravenously (0.25 and 0.75 microgram.kg-1.h-1), a hypovolemia-induced sustained depression of the secretion was observed even during ACE inhibition. Direct electrical stimulation (3 Hz, 5 V, 5 ms, bilaterally) of the peripheral splanchnic nerves decreased duodenal mucosal alkaline secretion to approximately 60% of the control level and increased mean arterial pressure by approximately 20 mmHg. However, in enalaprilate-pretreated animals, the inhibition of alkaline secretion due to splanchnic nerve stimulation was transient, a response that became sustained on angiotensin II substitution. These results suggest that the renin-angiotensin system prolongs the sympathoadrenergic inhibition of duodenal mucosal alkaline secretion and that angiotensin II, in this regard, acts mainly on the peripheral sympathetic efferents.

Hemodynamic, sympathetic and angiotensin II responses to PEEP ventilation before and during administration of isoflurane

BACKGROUND

Positive end-expiratory pressure (PEEP) ventilation and isoflurane anesthesia may opposingly affect the sympathetic nervous and renin-angiotensin systems. This study was performed to elucidate the modulatory effects of isoflurane anesthesia on the neurohumoral and cardiovascular responses to PEEP.

METHODS

Renin-angiotensin and sympathetic nervous activity were investigated in mechanically ventilated, normovolemic, chloralose anesthetized pigs before and during administration of 1.4% isoflurane. Arterial angiotensin II (AII) concentrations were measured and systemic, mesenteric, hepatic and renal spillover of norepinephrine (NE-SO) were calculated using isotope dilution. Regional hemodynamic variables were investigated in parallel.

RESULTS

PEEP10 alone moderately elevated AII levels (+12.5 +/- 4.9 pg/ml, P < 0.05) and increased systemic (+22 +/- 2.9 pmol.min.100 g-1, P < 0.05) and notably mesenteric (+32 +/- 9.6 pmol.min.100 g-1, P < 0.05) NE-SO. Blood flow decreased in all vascular beds studied. Except for in the liver, isoflurane generally reduced NE-SO compared to baseline but did not change AII concentrations. Strikingly, the sympathoexcitatory response to PEEP10 was inhibited, whereas AII increased markedly (+284 +/- 64 pg/ml, P < 0.05) during PEEP10 and isoflurane. Renal blood flow was significantly more reduced during PEEP10 and isoflurane compared to PEEP10 alone, whereas the magnitude of reductions were similar in the other vascular beds.

CONCLUSION

The data suggest that renin-angiotensin activation is important to attenuate the impact of PEEP ventilation on cardiovascular performance during administration of the sympathodepressant isoflurane. Interference with the renin-angiotensin system may cause cardiovascular decompensation in isoflurane anesthetized patients subjected to PEEP-ventilation.

Continuous measurement of gastric nitric oxide production

With the use of a double-lumen catheter, nitric oxide (NO) was dialyzed across a Gore-Tex membrane into a gas phase and subsequently analyzed on-line by chemiluminescence. This new technique for the continuous measurement of NO was evaluated bench-side and applied in the human stomach in vivo to measure the nonenzymatic formation of NO generated from nitrite in an acidic milieu. A linear relation (r2 = 0.991, P < 0.0001) between concentrations of NO in aqueous solutions (2.5-52.5 mM) and NO in the corresponding gas phases obtained by the dialysis technique (50-1,000 parts per billion) validated the present method for quantitative analyses of NO. Interassay and intra-assay coefficients of variation at all concentrations of NO for six experiments were < 5%. High intragastric concentrations of NO (in the micromolar range) were found during basal conditions. The requirement of both nitrite from the saliva and an acidic environment for NO formation is indicated, since depletion of saliva as well as acid neutralization greatly reduced gastric NO concentrations. Furthermore, large amounts of gastric NO were formed after intake of sodium nitrate. With the use of this technique, NO can be continuously measured with accuracy experimentally and clinically in any organ accessible to intubation.

A mechanism by which Helicobacter pylori infection of the antrum contributes to the development of duodenal ulcer

BACKGROUND & AIMS

Helicobacter pylori infection and duodenal ulcer disease are firmly correlated. However, the bacteria do mainly colonize the antrum, indicating an indirect pathogenic mechanism. The aim of this study was to test a concept claiming that H. pylori infection of the antrum selectively blocks normal inhibitory reflex pathways to gastrin and parietal cells.

METHODS

The effect of antral distention was studied on gastric acid secretion stimulated by pentagastrin and on gastrin release stimulated by gastrin-releasing peptide in H. pylori-infected and noninfected patients with and without duodenal ulcer disease, as well as after eradication of the bacteria.

RESULTS

The inhibitory effect on gastric acid secretion induced by antral distention was absent in H. pylori-infected patients irrespective of whether or not they had duodenal ulcer disease. The inhibitory mechanism was restituted in 8 of 10 patients within 9 months after successful eradication of H. pylori infection. Similar results were obtained in studies on gastrin release.

CONCLUSIONS

H. pylori infection blocks normal, physiological inhibitory mechanisms from the antrum to both the gastrin cells and to the parietal cell region, resulting in increased gastrin release and impaired inhibition of gastric acid secretion, which will probably lead to an increased duodenal acid load as a general prerequisite for the development of duodenal ulcer disease.

Sympathetic discharge to mesenteric organs and the liver. Evidence for substantial mesenteric organ norepinephrine spillover

This study using sampling of blood from the portal vein, in addition to arterial and hepatic sites, to estimate separately spillovers of norepinephrine from mesenteric organs and the liver in seven patients undergoing upper abdominal surgery. Conventional measurements in arterial and hepatic venous plasma provided a measure of net hepatomesenteric NE spillover (403 pmol/ml) that indicated a 13% contribution of these organs to total body spillover of NE into systemic plasma (3,071+/-518 pmol/min). The net hepatomesenteric spillover of NE into systemic plasma was much lower than the spillover of NE from mesenteric organs into portal venous plasma (1,684+/-418 pmol/min). This and the hepatic spillover of NE into systemic plasma (212+/-72 pmol/min) indicated a considerable combined spillover of NE from hepatomesenteric organs (1,896+/-455 pmol/min). The sum of the latter estimate with the difference between total body and net hepatomesenteric NE spillovers provided an adjusted total body spillover of NE into both systemic and portal venous plasma (4,564+/-902 pmol/min). Mesenteric organs made a 37% contribution, and the liver made a 5% contribution to the adjusted total body spillover of NE. Thus, a substantial proportion of total body sympathetic outflow is directed towards mesenteric organs; this is obscured by efficient hepatic extraction of NE (86+/-6%) when measurements are restricted to arterial and hepatic venous plasma.

Mechanisms behind changes in gastric acid and bicarbonate outputs during the human interdigestive motility cycle

Human gastric interdigestive acid and bicarbonate outputs vary cyclically in association with the migrating motor complex (MMC). These phenomena were studied in 26 healthy volunteers by constant-flow gastric perfusion, with continuous recording of pH and Pco2 in mixed gastric effluent and concomitant open-tip manometry of gastroduodenal motility. Stable acid and bicarbonate outputs were registered during less than 50% of the MMC cycle. Acid secretion started to increase 71 +/- 3% into the cycle, with maximum output during antral phase III. Bicarbonate output increased biphasically 1) 40 +/- 5% into the cycle, coinciding with reflux of bile, and 2) at the end of duodenal phase III when the aspirate was devoid of bile. The bicarbonate peak associated with phase III was abolished by atropine (0.01 mg/kg iv, n = 8) and by pyloric occlusion (n = 9) but remained unchanged after omeprazole (n = 10). The acid peak was abolished by both atropine and omeprazole. It is concluded that the MMC-related changes in acid and alkaline outputs represent two different and independent phenomena. Acid secretion cyclicity is due to periodical variations in cholinergic stimulation of the parietal cells. In contrast, the phase III-associated increase in bicarbonate output is due to duodenogastric reflux.

The pH/PCO2 method for continuous determination of human gastric acid and bicarbonate secretion. A validation study

BACKGROUND

The present paper describes and evaluates a methodologic approach for registration of the fast, interdigestive, motility-related changes in gastric acid and bicarbonate outputs seen in man.

METHODS

The technique is based on continuous gastric luminal perfusion and measurements of pH and PCO2 in gastric effluent and concomitant intragastric/duodenal manometry. Fourteen healthy volunteers participated.

RESULTS

Direct acid secretory estimations from pH recordings, corrected for hydrogen ion activity, correlated closely with values obtained by conventional titration. After intragastric infusion of bicarbonate, 96 +/- 5% of the newly measured steady-state value was registered virtually instantaneously provided that corrections for the PCO2 electrode time constant and the perfusion/aspiration time were made. In the neutral pH range (pH 5-7), practically full quantitative recovery of intragastrically infused bicarbonate was obtained. In the acid pH interval (pH 2-5) the recovery was significantly lower (53 +/- 6%; p < 0.01). With an aspirate without air admixture and during high perfusion rates (31 and 46 ml/min), full recovery of bicarbonate was obtained also at an acid pH, whereas a reduced perfusion rate (16 ml/min) significantly (p < 0.05) reduced the recovery rate.

CONCLUSIONS

With the pH/PCO2 technique both acid and bicarbonate assessments have a close to on-line time resolution. Acid output is measured accurately, but the method potentially underestimates actual bicarbonate levels in the acid pH range, a combined effect of diffusion of CO2 into air bubbles in the aspirate and into the gastric mucosa from the lumen. A high gastric perfusion rate minimizes this source of error. The pH/PCO2 technique is well suited for studies of the interaction between secretion and motility in the human stomach.

Gastric output of IgA in man: relation to migrating motility complexes and sham feeding

BACKGROUND/AIMS

The immunologic reactivity of the gastric mucosa is poorly understood. The origin and dynamics of immunoglobulin A (IgA) occurring in the gastric lumen were investigated in healthy, Helicobacter pylori-negative volunteers.

METHODS

Gastroduodenal manometric motility recordings were combined with gastric luminal perfusion, enabling calculation of gastric acid output and analysis of the total IgA output.

RESULTS

Acid output and total IgA correlated with the migrating motility complexes (MMC). The gastric IgA release showed maximal values in association with gastric motility phase III (maximal motor activity) and lowest values during phases I and II (none or irregular motor activity). The IgA output correlated with neither swallowed saliva (as indicated by amylase in the gastric perfusate) nor duodenogastric reflux (as indicated by gastric occurrence of bilirubin and/or duodenally infused PEG4000). Stimulation of gastric acid secretion by sham feeding during phase II-like motor activity (n = 6) induced a rapid and transient doubling of IgA output. There was no significant correlation between gastric acid secretion and gastric IgA release.

CONCLUSION

Substantial amounts of IgA are released into the human stomach, most likely originating from the gastric mucosa. The up-regulation of IgA release in association with the activity front of the MMC and anticipatory to food intake suggests a neuroendocrine control of gastric mucosal immune responses.