Intraluminal glucose: substrate for ischemic intestine

Transmural intestinal wall permeability in severe ischemia after enteral protease inhibition

In intestinal ischemia, inflammatory mediators in the small intestine's lumen such as food byproducts, bacteria, and digestive enzymes leak into the peritoneal space, lymph, and circulation, but the mechanisms by which the intestinal wall permeability initially increases are not well defined. We hypothesize that wall protease activity (independent of luminal proteases) and apoptosis contribute to the increased transmural permeability of the intestine's wall in an acutely ischemic small intestine. To model intestinal ischemia, the proximal jejunum to the distal ileum in the rat was excised, the lumen was rapidly flushed with saline to remove luminal contents, sectioned into equal length segments, and filled with a tracer (fluorescein) in saline, glucose, or protease inhibitors. The transmural fluorescein transport was determined over 2 hours. Villi structure and epithelial junctional proteins were analyzed. After ischemia, there was increased transmural permeability, loss of villi structure, and destruction of epithelial proteins. Supplementation with luminal glucose preserved the epithelium and significantly attenuated permeability and villi damage. Matrix metalloproteinase (MMP) inhibitors (doxycycline, GM 6001), and serine protease inhibitor (tranexamic acid) in the lumen, significantly reduced the fluorescein transport compared to saline for 90 min of ischemia. Based on these results, we tested in an in-vivo model of hemorrhagic shock (90 min 30 mmHg, 3 hours observation) for intestinal lesion formation. Single enteral interventions (saline, glucose, tranexamic acid) did not prevent intestinal lesions, while the combination of enteral glucose and tranexamic acid prevented lesion formation after hemorrhagic shock. The results suggest that apoptotic and protease mediated breakdown cause increased permeability and damage to the intestinal wall. Metabolic support in the lumen of an ischemic intestine with glucose reduces the transport from the lumen across the wall and enteral proteolytic inhibition attenuates tissue breakdown. These combined interventions ameliorate lesion formation in the small intestine after hemorrhagic shock.

Removal of luminal content protects the small intestine during hemorrhagic shock but is not sufficient to prevent lung injury

The small intestine plays a key role in the pathogenesis of multiple organ failure following circulatory shock. Current results show that reduced perfusion of the small intestine compromises the mucosal epithelial barrier, and the intestinal contents (including pancreatic digestive enzymes and partially digested food) can enter the intestinal wall and transport through the circulation or mesenteric lymph to other organs such as the lung. The extent to which the luminal contents of the small intestine mediate tissue damage in the intestine and lung is poorly understood in shock. Therefore, rats were assigned to three groups: No-hemorrhagic shock (HS) control and HS with or without a flushed intestine. HS was induced by reducing the mean arterial pressure (30 mmHg; 90 min) followed by return of shed blood and observation (3 h). The small intestine and lung were analyzed for hemorrhage, neutrophil accumulation, and cellular membrane protein degradation. After HS, animals with luminal contents had increased neutrophil accumulation, bleeding, and destruction of E-cadherin in the intestine. Serine protease activity was elevated in mesenteric lymph fluid collected from a separate group of animals subjected to intestinal ischemia/reperfusion. Serine protease activity was elevated in the plasma after HS but was detected in lungs only in animals with nonflushed lumens. Despite removal of the luminal contents, lung injury occurred in both groups as determined by elevated neutrophil accumulation, permeability, and lung protein destruction. In conclusion, luminal contents significantly increase intestinal damage during experimental HS, suggesting transport of luminal contents across the intestinal wall should be minimized.

The value of early enteral nutrition in the prophylaxis of stress ulceration in the severely burned patient

A retrospective analysis of prospectively collected data was performed to compare the frequency of upper gastrointestinal bleeding (GIB) in seriously burned patients treated with either cimetidine and antacids or enteral nutrition for ulcer prophylaxis. Five hundred and twenty-six seriously burned patients admitted to the burn intensive care unit of the BG Trauma Centre Ludwigshafen during a 4-year period were included into the study. All patients admitted to the burn unit from 1989 to 1991 received i.v. cimetidine (400 mg q4) for ulcer prophylaxis. If the intragastric pH dropped below 3.5, gastric pH was titrated with antacids up to > or = 4 via nasogastric tube. During the second 2-year period (1992-1993) early enteral nutrition alone was regarded to be ulcer protective and no further interventions for ulcer prophylaxis were routinely performed. Signs of overt upper GIB were monitored and documented through the entire study period. The overall occurrence rate of upper GIB in the cimetidine/antacids (C/A) group (n = 253) was 8.3 per cent with six cases of serious bleeding in five patients (1.98 per cent). In the enteral nutrition (EN) group (n = 273) the overall incidence of GIB was 3.3 per cent with two cases of serious bleeding (0.73 per cent). There were no deaths directly related to ulcer haemorrhage. The difference in the overall frequency of overt GIB between the groups studied was statistically significant (< 0.05). In our experience, early enteral nutrition is effective in the prevention of stress haemorrhage in the upper gastrointestinal tract. Additional medicinal prophylaxis is not required in burn patients.

Current theories of pathogenesis and treatment of nonocclusive mesenteric ischemia

Nonocclusive mesenteric ischemia (NOMI) is a poorly understood condition marked by progressive intestinal ischemia leading to infarction, sepsis, and death in a high proportion of patients. The mortality rate for this intestinal disorder remains high, even when the diagnosis is made early in the disease course. This paper presents a comprehensive review of NOMI with a detailed discussion of its history, pathophysiology, diagnosis, and treatment.

Intestinal ischemia: treatment by peritoneal lavage with oxygenated perfluorochemical

Though the delivery of elemental oxygen to tissues ravaged by anaerobic infection may be useful, little data exists that suggests that such therapy may benefit ischemic tissue. We report the development of a model to test the question that peritoneal lavage with an oxygen containing solution may favorably influence occlusive intestinal ischemia. Adult Sprague-Dawley rats with Nembutal (sodium pentobarbital) anesthesia underwent midline laparotomy; a microvascular clamp was applied to the superior mesenteric artery (SMA); and an inflow and outflow lavage catheter was placed. Treatment groups included control rats undergoing SMA occlusion only without lavage, rats lavaged with albumin during SMA occlusion (medium control), and rats lavaged during SMA occlusion with oxygenated perfluorochemical FC-47 emulsified in albumin (O2-FC-47). The increase in serum L-lactate following occlusion was used as an index of intestinal injury whether the perfusate was maintained at room temperature (28 degrees C) or body temperature (37 degrees C). Beginning with time O, which corresponded to the time of unclamping, subsequent samples were collected at 15, 30, and 60 minutes after a 30-minute SMA occlusion. Sequential lactates in 13 control rats were 4.18, 4.10, 3.88, and 4.52 mmol/L. Albumin lavaged animals had values at 28 degrees C of 2.23, 1.35, 1.8, and 2.44 mmol/L and values at 37 degrees C of 2.22, 1.40, 2.07, and 3.21 mmol/L, respectively. With O2-FC-47 lavage the respective lactates were 1.89, 1.09, 1.32, and 1.44 mmol/L at 28 degrees C and 2.14, 2.19, 2.50, and 2.1 mmol/L at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dimethyl sulfoxide on the function and structure of the intact and ischemic canine ileum

The action of dimethyl sulfoxide (DMSO) was investigated employing an experimental model of intestinal perfusion in vivo of isolated loops of dog ileum before, during, and following 1-h ischemia. DMSO was administered either into the intestinal lumen or by a continuous injection via a branch of the artery supplying the experimental loop. In the intact intestine, intraluminal DMSO significantly decreased the net movement of water, electrolytes, and glucose without affecting either the active transport of phenylalanine and beta-methylglucoside or morphology. This inhibition was irreversible since, following DMSO removal, there was only partial recovery of water absorption, while the other parameters remained significantly low. Inhibition by DMSO was delayed when the substance was injected intraarterially (i.a.). Regardless of its route of administration, DMSO did not reduce the extent of ischemic injury in comparison with non-treated "Controls": during ischemia, all functional parameters were practically non-existent. Following the re-establishment of circulation, a net loss of water and electrolytes ensued, and active transport did not improve. In both instances, the structural alterations were those associated with ischemia of the experimental model employed: short, broad, club-shaped villi which had completely lost their epithelium, but fairly intact crypts. It can be concluded from the data presented that in the dog DMSO inhibits absorption in the intact ileum and exerts no protection against ischemic lesion.

The role of glucose in preventing stress gastric mucosal injury

Reports from other investigators have shown the ability of pretreatment with either parenteral (glucose) or enteral (bolus Vivonex HN) nutrition to protect against stress ulcer formation, suggesting that the mechanism of protection may be substrate availability. However, these prior animal studies have used inordinately high amounts of Vivonex HN (equal to 1050 ml/hr in a human). This study compared cytoprotection afforded by pretreatment with a continuous infusion of Vivonex HN at a more clinically applicable level to that of both parenteral (ip) and enteral (po) glucose to test the above hypothesis. One hundred eight rats were infused (0.1 ml/min) for 30 min with: po water, ip water, po 25% glucose, ip 25% glucose, or po Vivonex HN. This was followed by 2 hr of cold-restraint stress. Serum glucose was determined. Poststress, animals were sacrificed, stomachs inspected, and mean ulcer index was calculated. Only oral 25% glucose offered significant gastric cytoprotection. Serum glucose was highest in both glucose groups.

CONCLUSIONS

(1) Vivonex HN pretreatment failed to cytoprotect in this model, (2) gastric cytoprotection by oral but not by parenteral glucose in the presence of similar serum glucose levels suggests that luminal factors, in addition to substrate availability, are necessary for this protection to occur.

Response of the intestinal mucosa to ischaemia

Images

Epithelial lesions in low flow states: a unifying concept

Several epithelium-lined organs are highly vulnerable in low flow states, and may lead to lesions such as hemorrhagic enteritis, stress ulcer, renal tubular necrosis, acalculous cholecystitis and "shock lung". A hypothesis is presented which postulated that the redistribution of the subepithelial microcirculatory blood flow and the subsequent damage to the epithelial barrier are the crucial processes in their pathogenesis. Presently available evidence in support of this thesis is summarized.

Protection of the intestinal mucosa during ischaemia by intraluminal perfusion

The function of the intestinal mucosa immediately after one hour's ischaemia was examined by means of tests in vivo and in vitro. During the ischaemia, the intestinal loop was perfused with media of different compositions, in an attempt to assess which provided the best protection of the epithelium from the deleterious effects of the ischaemia. The absorption of water, ions and glucose was then monitored in vivo, and the uptake of phenylalanine and beta methyl-glucoside by slices of mucosa was determined in vitro. The unprotected mucosa loses all active transport capacity in vitro following one hour's ischaemia, and is the site of a pronounced loss of water and ions into the lumen in vivo. Glucose absorption in vivo is also abolished. If the loop is perfused during the ischaemia with glucose-containing Krebs bicarbonate buffer, much of the transport capacity in vitro is retained; the loss of ions and water is prevented, and glucose absorption in vivo occurs. Perfusion during the ischaemia with other media, such as isotonic mannitol, Krebs bicarbonate buffer, or Ringer-lactate solution, results in a marked protection of the mucosa, in comparison with the unperfused loop, but the effects are not as pronounced as those of the glucose-containing buffer. It is concluded that the act of perfusing the intestine is the most beneficial factor, but that the presence of glucose in the perfusate does afford added protection.

"A spoonful of sugar" - trans-alveolar nutrition

In this initial study, it has been postulated that even the simple bronchial administration of isotonic glucose and insulin can maintain alveolar cell metabolism as measured by A.T.P. activity; further studies, using aerosolized glucose solutions, will test the validity of the hypothesis that alveolar metabolism can be maintained by the administration of substrate in aerosolized form by the alveolar route and will determine whether this form of substrate administration has clinical potential.

The roles of intraluminal chyme and vasomotor response in the pathogenesis of non-occlusive intestinal infarcts

The purpose of this study is to clarify the role of intraluminal chyme and the splanchnic vasomotor reaction on the pathogenesis of non-occlusive intestinal infarcts. In 5 mongrel dogs, 3 types of intestinal loops were created. A cervical loop, which is a heterotopic autotransplant of a segment of intestine, contains no chyme and is disconnected from the splanchnic innervation. A Thiry-Vella loop simultaneously constructed in the abdomen is also devoid of intraluminal chyme, but is still innervated. The intestine-in-continuity possesses both splanchnic innervation and intraluminal chyme. Hemorrhagic shock was then induced and the morphological response of the three types of intestine examined. The results indicate that the cervical loop is least damaged, whereas both the Thiry-Vella loop and the intestine-incontinuity are both severely damaged. It is concluded that in the non-occlusive hemorrhagic infarction of the intestinal mucosa, the peculiar splanchnic vasomotor response plays the dominant role. The pathogenesis of non-occlusive intestinal infarcts and its clinical implications are discussed.