Increases in intestinal glucose absorption and hepatic glucose uptake elicited by luminal but not vascular glutamine in the jointly perfused small intestine and liver of the rat

1. Previous studies have shown that an arterial-to-portal glucose concentration gradient may be an important signal for insulin-dependent net hepatic glucose uptake. It is not known whether intestinal factors also contribute to the regulation of hepatic glucose utilization. This problem was studied in a newly developed model which allows luminal perfusion of the small intestine via the pyloric sphincter and a combined vascular perfusion of the small intestine via the gastroduodenal artery and superior mesenteric artery, and of the liver via the hepatic artery and portal vein. 2. In both the presence and the absence of 1 mM-glutamine in the vascular perfusate, only about 7% of a luminal bolus of 5500 mumol (1 g) of glucose was absorbed by the small intestine, and nothing was taken up by the liver. 3. With small doses of 75-380 mumol (11-55 mg) of luminal glutamine, but not with 300 mumol of alanine, the intestinal absorption of the luminal glucose bolus was increased almost linearly from 7% to a maximum of 40% and the hepatic uptake from 0% to a maximum of 22%. 4. The increase of hepatic glucose uptake caused by luminal glutamine was only observed when the glucose load was applied into the intestinal lumen, rather than into the superior mesenteric artery. 5. The relative hepatic glucose uptake (uptake/portal supply) was enhanced from 0% to 55% with an increase in portal supply by luminal glutamine, whereas with a similar range of portal glucose supply the relative hepatic uptake by the isolated liver, perfused simultaneously via the hepatic artery and portal vein, was slightly decreased, from 20% to 15%. 6. Addition of various amounts of portal glutamine and/or alterations in the Na+ content of the portal perfusate failed to mimic the luminal glutamine-dependent activation of hepatic glucose uptake. Therefore the luminal-glutamine-elicited activation of hepatic glucose uptake was apparently not caused by a simple increase in the portal-arterial glucose gradient, by glutamine itself or by Na(+)-dependent alterations in hepatic cell volume. The results suggest that luminal glutamine caused not only an increase in intestinal glucose absorption by unknown mechanisms but also the generation of one or more humoral or nervous 'hepatotropic' signals in the small intestine which enhanced the hepatic uptake of absorbed glucose.

[The microhemodynamics and lymph flow in the small intestine under the action of histamine against a background of water loading and hyperthermia in dogs]

In anesthetized dogs, an increase of the lymph flow and the transcapillary fluid transfer, under the effect of histamine, was due to elevation of capillary hydrostatic pressure and capillary filtration coefficient in the small intestine. Against the background of water load and hyperthermia, histamine induced less obvious shifts of the microhemodynamic parameters and lymph flow in the small intestine.

Sequence of morphological alterations in a small intestinal ischaemia/reperfusion model of the anesthetized rat. A light microscopy study

Previous studies have shown serious mucosal damage and destruction to be associated with intestinal ischaemia/reperfusion. As both destruction and concomitant regeneration can be observed together in this potentially lethal condition we have studied the development and sequence of events by evaluating morphological changes of the small intestine in an ischaemia/reperfusion model in anaesthetized rats. Forty-five minutes of ischaemia was followed by 4 hours of reperfusion. Tissue samples of the small intestine were examined by light microscopy in normal and semithin sections. Samples were collected at the end of ischaemia, at 10 min, and at 1, 2, 3 and 4 hours of reperfusion, respectively. Survival was assessed in a parallel group of anaesthetized rats. The morphological changes were described and they were analysed by a semi-quantitative method using five different markers of histological alteration. The mortality rate of a control survival group was 100%. Mucosal destruction at the end of ischaemia and during reperfusion was diffuse and steadily increased as a function of reperfusion time. At the same time the epithelium showed intensive regenerative growth which covered the denuded mucosal surface by the third hour of reperfusion. A secondary epithelial desquamation followed this process and was accompanied by heavy inflammatory cell infiltration. The infiltration may be the cause of the secondary epithelial injury.

[A scanning electron microscopic study on experimental ischemic lesions in dogs]

Occlusion of minute vessels in the bowel wall is thought to be a cause of ischemic lesions. This study was performed to clarify the pathohistology and the morphology of these various lesions. Microbarium suspension was injected into the mesenteric vessels of twenty four dogs and the ischemic lesions were produced experimentally. The degree of the bowel damage was parallel to the amount of injected microbarium suspension. The resected specimen of the various stages of the disease was studied histologically and morphologically by a scanning electron microscopy. With the small amount of barium suspension the lesions were confined to the mucosal layers. The epithelial cells regenerated regularly and the villi normalized rather quickly, and these lesions healed within one to two weeks (transient form). With the large amount of barium suspension the lesions involved both submucosal and muscular layers. The epithelial cells regenerated irregularly and the villi rearranged to abnormal forms. These lesions healed in two to four weeks leaving the stenosis due to scar formation (stricturing form). This study suggests that scanning electron microscopic investigation can be used to assess the details of morphological changes of ischemic mucosa, special reference to the degeneration and regeneration process of epithelium of the villi.

[An animal model of posttraumatic multiple system organ failure (MSOF)]

Hemorrhagic shock, sepsis, excessive systemic inflammatory reactions, and failure of intestinal mucosal barrier function are known to be major predisposing factors in the development of MSOF in patients after severe trauma or burns. We investigated the possibility of complicating clinically simulating MSOF in animals. Our results showed that, with compounded traumatic factors, including damages to the bowel, and proper circulatory and respiratory support, an animal model which simulated the pathophysiology and histopathology of MSOF could be reproduced to offer opportunity for the study of mechanisms and therapy. Markers of MSOF were also described for reference.

Intestinal villus microcirculatory response to hemorrhage in adult and immature rats

The response of the villus microcirculation to moderate hemorrhage was compared in adult and immature rats. As an estimate of villus blood flow, flux of red blood cells through the terminal arteriole loop at the villus tip was quantified in vivo using fluorescence epilumination videomicroscopy. Baseline red blood cell flux and mean arterial pressure (MAP) of immature rats (973 cells/s, 84 mm Hg) were significantly less than that of adults (1,435 cells/s, 131 mm Hg). Following hemorrhage of 30% of estimated blood volume, MAP of immature rats was still 24% less than that of adults; however, villus flux was not significantly different (578 cells/s immature, 640 cells/s adult; P = .63). Thus, as indicated by changes in villus flux, immature rats do not appear to be more susceptible to acute intestinal blood flow reduction induced by a single moderate hemorrhage. Immaturity of villus microvascular anatomy and of intestinal vasoregulatory mechanisms may account for the differential response.

Evaluation of a 20-MHz ultrasound transducer used in diagnosing porcine small bowl ischemia

The authors have previously demonstrated the ability of an 8.5-MHz linear array to detect moderate or severe intestinal ischemia in a porcine model. This study compares the ability of the 8.5-MHz linear array with a prototype miniature 20-MHz ultrasound (US) imaging probe in detecting small bowel ischemia. Five piglets were studied in which vascular clamps were applied to isolated jejunal pedicles, then released sequentially at hourly intervals to induce ischemia from 0 to 6 hours. After 24 hours of reperfusion, the tissue was removed and examined with both the 8.5-MHz linear array and the 20-MHz probe. A histologic examination also was done. The acoustical criteria used for interpretation were presence or absence of folds, number of echo layers, relative thickness of layers and homogeneity and continuity of layers. The 8.5-MHz system predicted the duration of ischemia with a kappa value of 0.66 +/- 0.03, whereas the 20-MHz system had a kappa value of 0.49 +/- 0.03. Both systems were able to distinguish normal or mild ischemia from moderate or severe ischemia with sensitivity and specificity rates of at least 94%. Both 8.5- and 20-MHz US systems detected intestinal ischemia in vitro. Further studies are indicated to determine the ideal frequency and design for a US system that can be used clinically.

Piggy-back mesenteric arterial reconstruction

Reimplantation of stenotic or occluded visceral arteries into the aorta is one solution to symptomatic chronic visceral ischemia. We report a patient in whom the associated problem of small bowel infarction precluded prosthetic reconstruction and saphenous vein was unavailable. Reimplantation of the celiac artery into the aorta was combined with piggy-back reimplantation of the superior mesenteric artery into the side of the celiac artery to provide successful revascularization of the small bowel. A 16-month angiographic and 5-year clinical follow-up is provided.

[Enteroscopy: methods and results]

Recent advances in the instrumentation and techniques of enteroscopy now permit examination of the small bowel. This report is on the use of a prototypic small bowel enteroscopy to investigate patients with gastrointestinal bleeding of obscure origin. We used the sonde-type enteroscope (Olympus Corp.) that migrates distally responding to peristaltic activity. This instrument has neither tip deflection controls nor interventional capability. Small bowel enteroscopy was performed in 17 patients. Arteriovenous malformations were visualized in 5 patients but three of them suffered from Rendu-Osler disease. Small bowel enteroscopy can be useful in the evaluation of patients with gastrointestinal bleeding of obscure origin. However, patients must be well selected on basis of negative routine examinations because this method is time-consuming.

Recurrent gastrointestinal bleeding due to angiodysplasias in the small bowel. Experience with panendoscopic diagnosis and treatment in 6 patients

Detection of bleeding from angiodysplasias located in the small bowel remains a diagnostic challenge. Intraoperative panendoscopy of the small bowel is a safe method with high diagnostic yield. The experience with this technique in 6 patients with overt bleeding or melena is described. During the panendoscopy a suture technique was used as therapeutic modality. This method is easy, cheap, does not require special skills or instruments, and the result is seen immediately.

Small bowel transplantation in the mouse: development of a model

The rat has been used as a model to study the significance of graft and host interactions in small bowel transplantation (SBTX). A mouse model of SBTX would allow investigators to apply the knowledge of the well-defined genetics in the mouse to this field of study. Therefore, we have developed a mouse model of heterotopic SBTX using syngeneic C57BL6/J mice. Animals were anesthetized with a combination of ketamine and xylazine. Donor animals underwent midline laparotomy, with isolation of a segment of bowel as an isograft for transplantation to a recipient animal. The bowel was flushed in situ prior to removal of the graft with a Carrel patch of aorta and portal vein. The recipient animal underwent midline laparotomy and preparation of its infrarenal aorta and inferior vena cava for end-to-side anastomosis of the graft with 10-0 nylon. After vascular reperfusion of the graft the ends of the isografted bowel were brought out as stomata. Successful grafts were later assessed for viability by laparotomy or histological examination at the time of sacrifice. Areas of technical difficulty in this model and issues that might improve the experimental results are discussed. This model should allow investigators to apply the well-defined genetics of the mouse to probe the challenging field of intestinal transplantation.

Surgical approach to occult gastrointestinal bleeding

In 5% of patients with gastrointestinal bleeding, standard evaluation fails to reveal the source of the bleeding. We describe the management of 71 patients treated for obscure gastrointestinal bleeding at the Mount Sinai Medical Center, New York, New York, from 1985 to 1991. There were 38 men (54%) and 33 women (46%). The mean age was 60 years. The patients had bleeding episodes for a mean period of 26 months and required an average of 20 units of blood prior to surgical treatment. All had undergone an extensive diagnostic workup including barium contrast studies, endoscopies, and angiographies. Some had multiple bleeding scans, Meckel scans, and surgical explorations. Three patients were found to have "watermelon stomach" on endoscopy and had an antrectomy. Sixty-eight (96%) patients underwent a preoperative small bowel enteroscopy, which revealed the precise diagnosis in 50 (70%) of the patients. All patients underwent surgery. In 30 (42%) patients in whom the bleeding site was not apparent at exploration, intraoperative enteroscopy was performed. Two actively bleeding patients had intraoperative enteroscopy, which failed to localize the bleeding site, and intraoperative scintigraphy was utilized. The bleeding was found to originate in small bowel arteriovenous malformation (AVM) (28 patients), leiomyoma (8 patients), primary small bowel malignancies (11 patients), and other causes (24 patients). Fifty-six patients (80%) had no further bleeding; 9 with multiple small bowel AVM have experienced rebleeding and are alive. Six patients died of recurrent bleeding, and six died of metastatic cancer. An aggressive approach should be applied in patients in whom standard evaluation fails to localize the source of gastrointestinal bleeding. Enteroscopy, surgical exploration with additional intraoperative enteroscopy, and occasional intraoperative scintigraphy can achieve an excellent yield and allow resection and potential cure.

Effects of dexamethasone on glutamine metabolism in the isolated vascularly perfused rat small intestine

Post-stress metabolism is associated with a large glutamine (Gln) efflux from muscle and an increased Gln utilization by the small intestine. Both appear to be modulated by corticosteroids. The present investigation was performed to better characterize the mechanism of corticoid action on Gln metabolism in an isolated preparation of vascularly perfused rat small intestine. In all perfusions, a synthetic perfusate free from blood components was used with only 0.6 mM Gln and 10 mM glucose as substrates. Irrespective of dexamethasone concentrations in the vascular perfusate (none, 0.25 mg l-1, or 2.5 mg l-1, isolated intestines from normal rats exhibited unchanged extraction rates of Gln (-85 +/- 8, -89 +/- 10, and -87 +/- 16 nmol min-1 g-1) and unchanged production rates of alanine (43 +/- 9, 40 +/- 7, and 51 +/- 5 nmol min-1 g-1) and ammonia (49 +/- 15, 45 +/- 13, and 54 +/- 13 nmol min-1 g-1). Similarly, when intestines were vascularly perfused 2 or 9 days after dexamethasone injection (0.45 mg kg-1 BW), net Gln uptake also remained unchanged (-88 +/- 16 and -84 +/- 11 nmol min-1 g-1). There was, however, a shift in nitrogenous products of Gln metabolism from ammonia (-31% and -38%) to alanine (+16% and +64%). Thus, the failure of dexamethasone to increase Gln uptake in the isolated rat intestine may indicate that rather than acting directly on the mucosa, dexamethasone could regulate intestinal Gln consumption in vivo by indirect mechanisms possibly involving extramucosal tissues. Dexamethasone pretreatment may modulate the pattern of nitrogenous products in portal venous blood presented to the liver and thus support enhanced nitrogen loss through ureagenesis by metabolic cooperation between gut and liver.

Organ blood flow in Fischer-344 rats bearing MCA-induced sarcoma

Although blood flow is central to systemic metabolism, little is known about the effect of tumor on the perfusion of host tissues. This study evaluated the effects of a methylcholanthrene-induced sarcoma on blood flow to intra-abdominal organs and skeletal muscle of Fischer-344 rats anesthetized with pentobarbital sodium. Animals were studied by aortic injection of radiolabeled microspheres when the tumors reached 20% of body weight. Total-organ arterial flows in spleen, liver, small intestine, and pancreas were each increased to 50-150% in tumor bearers relative to controls (P less than 0.05). Portal venous flow and flow per gram to hindlimb muscle were 60 +/- 20 and 300 +/- 100% greater, respectively, in tumor-bearing animals (P less than 0.005). This study shows that tumor growth can be associated with large changes in organ flow and distribution of cardiac output. The increase in skeletal muscle flow in the tumor bearers, which lost normal tissue weight relative to pair-fed controls (P less than 0.05), is in marked contrast to decreased muscle flow previously observed in simple starvation.

Atherosclerotic occlusive disease of the superior mesenteric artery: late results of reconstructive surgery

Between 1975 and 1988, 103 patients underwent reconstruction of the superior mesenteric artery for atherosclerotic occlusive disease. Patients undergoing revascularization with associated mesenteric infarction were excluded. There were 89 men and 14 women whose mean age was 57.2 years. Six patients were operated on emergently for impending mesenteric infarction; six patients underwent revascularization after intestinal resection for ischemic lesions; 20 patients had typical abdominal angina; 39 patients had nonspecific abdominal symptoms, and 32 patients underwent revascularization of their superior mesenteric artery for asymptomatic lesions. Revascularization of the celiac axis and inferior mesenteric artery was associated in 36 and four cases, respectively. Four patients (4%) died postoperatively. Four early occlusions (4%) were observed. During the follow-up period (mean = 69 months), 18 patients died; five patients had recurrent intestinal ischemic symptoms, four of whom died. All surviving patients underwent follow-up duplex scanning, examination, and arterial or venous digitalized angiograms in selected cases. Nine patients (9%) had anatomical abnormalities: two stenoses and seven occlusions. Failure of revascularization of the superior mesenteric artery was observed in patients with severe initial intestinal ischemia. Late complications were not statistically significantly related to the different techniques of revascularization used.

Inhibition of post-ischemic reperfusion injury of the small intestine by diamine oxidase

To elucidate the role of diamines in the pathogenesis of post-ischemic reperfusion-induced tissue injury, the effect of diamine oxidase was studied in the rat whose superior mesenteric artery was occluded for 15 min followed by 30 min reperfusion. Kinetic analysis using radiolabeled albumin revealed that the mucosal permeability of the reperfused small intestine increased significantly. Histological examination of the reperfused intestine revealed a marked degeneration of its mucosal layer. Intravenous administration of diamine oxidase inhibited the reperfusion-induced increase in mucosal permeability of the intestine almost completely and preserved the structure of the small intestine. H1-antagonist chlorphenilamine and H2-antagonist famotidine also inhibited the reperfusion injury of the small intestine. These and other results suggested that extracellular diamines might play critical roles in post-ischemic reperfusion-induced injury of the small intestine.

Xanthine oxidase formation during experimental ischemia of the equine small intestine

We hypothesized that xanthine oxidase plays a role in the postischemic reperfusion injury in the equine small intestine. Under anesthesia, four horses and two ponies underwent ischemic strangulating obstructions of segments of the proximal jejunum, mid-jejunum and ileum. Prior to vascular occlusion, and at 1 h and 2 h of ischemia, full-thickness intestinal biopsies were collected for histopathological evaluation and for determination of combined xanthine dehydrogenase (XDH) plus xanthine oxidase (XO) activity, and XO activity alone. The level of XO activity was expressed in percentage according to the ratio of XO/(XDH + XO). We found a nearly threefold increase in the combined level of XDH plus XO activity from ileum to duodenum (p less than 0.04). However, the preischemic level of % XO activity did not vary significantly (p = 0.61) between segments of jejuno-ileum. Likewise, no significant difference was noted between intestinal segments after ischemia. Therefore, the data from all intestinal segments were pooled for each time and analyzed using Wilcoxon's signed rank test (one-tailed). Compared to the pre-ischemic level of % XO activity (median 27%), the % XO activity increased after 1 h of ischemia (median 37.0%), reaching statistical significance (p = 0.016). There were no statistical differences between the preischemic % XO activity and the % XO activity in non-ischemic bowel at the end of the anesthetic period. During ischemia, % XO activity increased, which lends credence to the importance of xanthine oxidase in previously-documented reperfusion injury in the equine small intestine.

Superoxide dismutase promotes ATP and GTP restoration of rat small intestine during postischaemic reperfusion

The small intestine of rats was prepared according to a procedure which is taken for preservation and transplantation in clinical practice. The blood supply of the rat intestine was completely interrupted for 30 min in situ. During this period the lumen of the intestine was rinsed with Ringer-lactate solution. This ischaemic period was followed by 10 min of reperfusion. As a result a decrease in ATP, and GTP concentrations, and of the total adenine nucleotide content during the preservation period occurred. In animals pretreated with superoxide dismutase (i.v. application; superoxide dismutase preparation from human erythrocytes) an accelerated restoration of nucleotide concentrations during the reperfusion period was observed. From the beneficial effect of superoxide dismutase it can be concluded, that there is a considerable formation of active species of oxygen which disturb the energy generation by the mitochondrial respiratory chain during ischaemia/re-oxygenation.