Inhibitory effect of intragastric glucose on gastric acid secretion and gastric emptying of liquids in man. Role of endogenous somatostatin, gastrin, and insulin

Acute gastric injury after ingestion of substrate with hyperosmolar glucose and benzoate inversely related with small intestinal bacterial overgrowth

BACKGROUND/AIMS

The occurrence of gastrointestinal symptoms and the presence of small intestinal bacterial overgrowth (SIBO) could be determined after ingestion of substrate with highly concentrated glucose for glucose breath test (GBT), after which endoscopic images for acute gastric injury have not been clarified. The aims of this study were to investigate the prevalence and relationship of acute gastric injury with SIBO after GBT.

MATERIALS AND METHODS

A cohort of 235 patients with functional gastrointestinal symptoms undergoing breath test with 50 g glucose solution, immediately followed by upper endoscopy were surveyed. The acute gastric injury in endoscopic images and the GBT for hydrogen (H2) or methane (CH4) were assessed.

RESULTS

The prevalence of acute gastric injury was 28.1% (66/235) after GBT. There were significant differences in GBT positivity (+) with and without gastric injury (25.8% vs 40.8%, p=0.03). In subtypes, GBT (H2) + was significantly lower in group with gastric injury than in the group without. No differences were seen in GBT (CH4) + between two groups. On multivariate analysis, the subtype of GBT (H2) + (Odds ratio (OR)=0.42; 95% Confidence interval (CI)=0.20-0.90; p=0.03) inversely and female (OR=2.11; 95% CI=1.11-4.00; p=0.02) were significantly related with gastric injury. Whereas gastric injury was the only independent related factor for GBT + inversely (OR=0.51; 95% CI=0.27-0.97; p=0.04).

CONCLUSION

Highly concentrated glucose might provoke acute gastric injury, which could predict the absence of SIBO.

Are gastric, jejunal, or both forms of enteral feeding gastroprotective during stress?

BACKGROUND

Clinical data suggest enteral nutrition prevents stress ulceration and intragastric nutrients prevent restraint-induced gastric injury. The purpose of these studies was to determine if jejunal nutrients can protect without gastric contact and to determine if gastric pH, motility, or mucosal perfusion is affected.

METHODS

In Experiment 1, 27 rats were restrained for 2 h at room temperature followed by 2 h in cold (4 degrees C), with intragastric (IG) or intrajejunal (IJ) 2 ml/h infusions of saline or 25% glucose. Gastric lesions, pH, volumes, and glucose concentrations were measured postmortem. In Experiment 2, 23 rats had gastric strain gauges implanted >5 days prior to a 0.5 ml/h IG or IJ infusion during stress. In Experiment 3, 40 rats were anesthetized for laser Doppler measurements of gastric mucosal perfusion and arterial catheter monitoring of systemic hemodynamics. Rats received 0.5-ml boluses of concentrated glucose or saline IG or IJ, and were monitored for 60 min.

RESULTS

(1) The 2 ml/h IJ and IG glucose infusions prevented gastric injury, but the elevated gastric glucose concentrations suggested equal gastric contact. (2) The 0.5 ml/h glucose IG and IJ infusions decreased gastric injury without reflux of the IJ glucose into the stomach and suppressed stress-induced hypercontractility, but not acidity. (3) Systemic perfusion pressures were unaffected by enteral glucose. IG glucose had little effect on gastric mucosal perfusion, while IJ glucose decreased gastric perfusion within 5 min.

CONCLUSIONS

These studies show that large volumes of enteral glucose prevent restraint injury but IJ glucose refluxes into the stomach. The gastroprotective effects of small, nonrefluxing volumes of IJ glucose are associated with suppression of stress-induced gastric hypercontractility, but not with suppressed acidity or enhanced perfusion.

Gastric emptying in diabetes mellitus: relationship to blood-glucose control

The application of novel investigative techniques has established that disordered gastric motility is a frequent complication of diabetes mellitus. Thus, gastric emptying of solid or nutrient liquid meals is abnormal in 30% to 50% of randomly selected outpatients with long-standing type 1 or type 2 diabetes. Delayed gastric emptying occurs more frequently than rapid emptying. There is increasing evidence that disordered gastric motility has a major impact on the management of patients with diabetes mellitus by leading to gastrointestinal symptoms and poor glycemic control. Although both gastroparesis and upper gastrointestinal symptoms have been attributed to irreversible autonomic damage, it is now clear that acute changes in the blood-glucose concentration have a major effect on both gastrointestinal motor function and the perception of sensations arising in the gut. For example, there is an inverse relationship between the rate of gastric emptying and the blood-glucose concentration, so that gastric emptying is slower during hyperglycemia and accelerated during hypoglycemia. This article reviews some issues in the etiology, diagnosis, and management of problems associated with gastric emptying in elderly persons with diabetes mellitus.

Plasma molecular forms of gastrin, neurotensin and somatostatin in pregnancy and gestational diabetes after an oral glucose load or a mixed meal

At present the physiological role of gastrin, neurotensin and somatostatin in pregnancy and gestational diabetes is scarcely known. We have measured their different molecular forms in plasma of six female controls, six normal pregnant (NP) women and six gestational diabetic (GD) women under basal conditions and 30 min after an oral glucose load (100 g) and a liquid mixed meal in order to study if their alteration could contribute to the impaired glucose tolerance in GD. Total basal concentrations of neurotensin and somatostatin were higher in GD than in controls and NP, and no change was found after the glucose load or mixed meal in GD. Neurotensin-1-13 was the main molecular form of all neurotensins at basal time in the three groups studied, being higher in GD in comparison with controls and NP. Somatostatin-1-14 was the predominant molecular form in controls and GD under basal conditions and did not show any change any change after stimuli. In NP, somatostatin-1-14 showed a significant increase following both kinds of stimuli. Total gastrin concentrations in NP and GD showed a significant increase after the glucose load, which was not observed in controls. Gastrin-17 was the main molecular form at basal time and 30 min post-stimuli in GD but not in NP and controls. We suggest that the basal elevation of neurotensin and somatostatin levels could contribute to the impaired glucose tolerance observed in gestational diabetes, as well as to the lack of post-stimuli responses for neurotensin and somatostatin in GD.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of intragastric and intravenous glucose on restraint model of stress ulceration

Intragastric glucose prevents acute stress-induced gastric mucosal injury in the restrained rat. Because increased gastric contractions contribute to mucosal injury in this model and because parenteral glucose infusions have been shown to suppress gastric contractility, we hypothesized that centrally mediated responses to hyperglycemia might contribute to the cytoprotective effect of intragastric glucose. We compared intragastric and intravenous 25% glucose with saline infusions during cold restraint and measured their impact on gastric lesions, serum glucose levels, gastric residual volume (an indirect indicator of net gastric contractility), acidity, and mucin concentration. We found that both intravenous and intragastric glucose infusions increased serum glucose to over 500 mg/dl after 4 hr of stress. Intragastric glucose increased residual volume and gastric pH, as well as decreased gastric mucosal injury, but intravenous glucose had no effects on gastric function. We found that none of the potentially protective effects of intragastric glucose are mediated by central responses to hyperglycemia, and likewise that intravenous glucose has no effect on gastric mucosal injury.

Intestinal fat does not inhibit gastric function through a hormonal somatostatin mechanism in dogs

In awake dogs with chronic gastric, duodenal, and jejunal fistulas, F(ab)1 fragments of somatostatin monoclonal antibody (mAb S607) were administered intravenously (IV) to test the hypothesis that intraintestinal lipid inhibits peptone-stimulated gastric acid secretion and emptying by a hormonal somatostatin mechanism. Plasma somatostatin was increased significantly by duodenal and jejunal perfusion with 20% lipid. Somatostatin administered IV caused dose-dependent inhibition of meal-stimulated gastric acid secretion and gastric emptying similar to that seen after intestinal perfusion with lipid. Administration of mAb S607 F(ab)1 fragments significantly reversed somatostatin (400 pmol.kg-1.h-1, IV)-induced inhibition of peptone-stimulated acid output and gastric emptying. Acid output inhibited by intraduodenal lipid was reversed partially after F(ab)1 administration, but the inhibitory effect of intrajejunal lipid was not altered. Inhibition of acid secretion by IV somatostatin and by intraintestinal fat was not caused by a decrease in circulating gastrin concentrations. Gastric emptying delayed by intraintestinal lipid was unaffected by antibody administration. Somatostatin does not appear to be a major hormonal mediator of intestinal fat-induced inhibition of gastric acid secretion or delayed gastric emptying in dogs.

Effect of ingested carbohydrate, fat, and protein on the release of somatostatin-28 in humans

The level of somatostatin-28, a bioactive peptide derived from pro-somatostatin in gastrointestinal epithelial cells, increases in human plasma after food intake. To determine if an equivalent response occurs with individual components of a mixed meal, somatostatin-28 and prosomatostatin, somatostatin-14, and somatostatin-13, in combination, were measured in healthy men before and after intake of (a) a mixed meal (715 kcal), (b) carbohydrate (100 g equivalent glucose), (c) protein (22 and 45 g), and (d) fat (25 and 50 g). After the mixed meal, somatostatin-28 levels doubled within 120 min and gradually declined by 4 h. With carbohydrate, somatostatin-28 levels were unaltered. After 22 and 45 g of protein, somatostatin-28 increased equivalently within 60 min, representing 30% of the amount with the mixed meal. With 25 g fat, a somatostatin-28 increase similar to that with the meal was seen; this response was doubled with 50 g fat. No changes in prosomatostatin, somatostatin-14, or somatostatin-13 were observed with the mixed meal or with the separate macronutrients. The authors conclude that fat is the major stimulus for somatostatin-28 secretion in humans and hypothesize that somatostatin-28 is an inhibitor of the endocrine and exocrine pancreas during nutrient absorption.

Somatostatin may not be a hormonal messenger of fat-induced inhibition of gastric functions

The present study was designed to evaluate somatostatin as a hormonal inhibitor of gastric functions in humans. Seven healthy volunteers were investigated on 6 separate days. Peptone meal-stimulated gastric acid secretion was measured by intragastric titration for 2 h and gastric emptying was estimated with a dye-dilution technique. The effect of intravenous administration of somatostatin at 0, 12.5, 50, 100, and 200 pmol/kg.h was investigated and related to the effect of intragastric administration of 100 ml of vegetable oil. Plasma somatostatinlike immunoreactivity was elevated during intravenous administration of somatostatin at 100 and 200 pmol/kg.h, whereas no increase was detected in response to the oil. Somatostatin infusion at 100 and 200 pmol/kg.h significantly inhibited the acid secretion by 25% and 65%, and the oil reduced the acid output by 41%. Somatostatin at 100 and 200 pmol/kg.h significantly enhanced gastric emptying, whereas the oil inhibited gastric emptying. These observations suggest that somatostatin may not be an important hormonal messenger of fat-induced inhibition of acid secretion or gastric emptying.

Absent postprandial duodenal motility in a child with cystic fibrosis. Correction of the symptoms and manometric abnormality with cisapride

A 19-mo-old boy with cystic fibrosis presented with a lifelong history of feeding problems and constipation, and an 8-mo history of episodes of repeated retching, diaphoresis, dehydration, and somnolence after eating. Tests of esophageal motility and gastric emptying of a 5% glucose meal were normal. Antroduodenal pressure recordings during fasting demonstrated the presence of all phases of the interdigestive motor complex. After consumption of a 240-ml complex liquid meal, however, the contractile pattern that generally accompanies eating was absent and gastric emptying was markedly delayed. When bethanechol or metoclopramide was given 10 min before the complex liquid meal, there was a paucity of contractile activity, gastric emptying was slow, and symptoms of lethargy, diaphoresis, and retching were present. When cisapride was given, there was frequent irregular contractile activity, faster gastric emptying, and no symptoms of lethargy. During the past year treatment with cisapride has been a requirement in order to prevent recurrence of the symptoms. Antroduodenal pressure studies proved helpful in the identification of a treatable manometric abnormality that was associated with symptoms of delayed gastric emptying.

Gastrointestinal somatostatin: distribution, secretion and physiological significance

Somatostatin-like immunoreactivity (SLI) has been found throughout the gastrointestinal tract in all species examined. In the stomach it is mainly present in endocrine-type D-cells whereas in the intestine there is also an extensive distribution in enteric neurones. In all regions of the gastrointestinal tract multiple forms of somatostatin exist. A precursor (prosomatostatin) has been partially sequenced, three forms with 20 (SS-20), 25 (SS-25) and 28 (SS-28) amino acids completely sequenced, and somatostatin-14 (SS-14) demonstrated by radioimmunoassay. Both SS-14 and SS-28 exert a wide range of actions on the gastrointestinal tract and there is strong supportive evidence for a role in the regulation of gastric acid and gastrin secretion, gastrointestinal motility and intestinal transport. Both in vivo and in vitro studies on the secretion of gastric SLI into the vasculature have shown that nutrients initiate the process but that subsequent events are regulated by a complex interplay between hormonal and neuronal pathways. GIP is one of the most potent hormonal secretagogues. In the stomach, acetylcholine, opioid peptides and substance P are probably involved in parasympathetic inhibitory pathways and gastrin releasing peptide in stimulatory pathways. The sympathetic nerves are also stimulatory. Regulation of secretion of intestinal SLI has not been so extensively studied. Although SLI is also found in the gastrointestinal lumen the significance is unclear. Despite these advances the exact route of delivery of somatostatin to its target organs is uncertain and paracrine, endocrine and neural pathways may all be involved.