Effects of peripherally and centrally applied ghrelin in the pathogenesis of ischemia-reperfusion induced injury of the small intestine

Ghrelin is an important hormone involved in the control of the human appetite center. Recently, protective properties of this hormone have been recognized in various models of impairment of the gastric mucosa, including stress, ischemia and reperfusion (I/R). Ghrelin is predominantly secreted by the gastric mucosa of stomach, but there are other sources of ghrelin, for example in the hypothalamus and various parts of the central nervous system (CNS) that should be taken into consideration. This hormone exerts biological effects via the activation of growth hormone secretagogue receptor (GHSR), the presence of which was confirmed in different parts of the gastrointestinal (GI) tract and midbrain structures. Although substantial evidence of the divergent biological effects of ghrelin and the mechanism of its action has been emphasized, the precise mechanisms of ghrelin which affords GI protection is still unclear. Particularly, there is a sparse amount of evidence concerning its action on the GI system. The major aim of the present study was to evaluate the importance of peripherally and centrally administered ghrelin at different times of the ischemia and reperfusion (I/R period in the modulation of resistance of the intestinal mucosa to the injury induced by ischemia and subsequent reperfusion. Secondly, we wanted to evaluate the possible mechanism of the action of ghrelin with a particular focus on its influence on the intestinal blood flow. Male Wistar rats were divided into 4 series (A-D) of the experimental groups (n=7). In series A the importance of peripherally administered ghrelin at different time of I/R period was studied. In series B the importance of centrally administered ghrelin at different time of I/R period was evaluated. In series C and D, the mechanisms of peripherally and centrally administered hormone were examined, respectively. Two models of the I/R period were selected: short lasting (30/60 min) and long lasting (60/120 min). The following drugs were used: ghrelin (50 μg/kg i.p. or 1 nmol in 10 μl i.c.v.), 6 hydroxy dopamine (50 mg/kg i.p.), nadolol (0.5 mg/kg i.p.), calcitonin gene related peptide fragment (CGRP(8-37), 100 μg /kg i.p.), capsaicin (5-10 mg/100 ml solution s.c.). The mesenteric blood flow (MBF-ml/min), the intestinal microcirculatory blood flow (LDBF-PU), the arterio-venous oxygen difference (AVO(2)-ml/O(2)/100 ml blood), and the intestinal oxygen uptake (VO(2)) in ml O(2)/min were measured. Mucosal impairment was assessed planimetrically with the use of a digital photo analyzer (LA) and histologically with the use of the six-point Park/Chiu scale. Peripheral administration of ghrelin evoked marked increase of MBF and LDBF by 42% and 48%, respectively, with significant reduction of LA by 38%. When ghrelin was administered at the beginning of the reperfusion period during the short I/R period or prior to the long lasting I/R period, the vascular reactions and protective effects were reduced, but not completely abolished. The central administration of ghrelin before the short I/R period significantly increased the MBF and LDBF by about 32% and 35%, respectively, as well as LA reduction by about 20% in comparison to the control group. However, when ghrelin was administered prior to the long I/R period or after the onset of completed ischemia, neither vascular nor protective effects were noticed. Sensory denervation and the blockade of the CGRP1 receptors totally blocked the protective and hyperemic effects of the peripherally administered ghrelin. Selective blockade of the adrenergic system or blunting of the vagal nerves (vagotomy) significantly but not totally eliminated the effects of centrally applied ghrelin, which were abolished when both adrenergic and parasympathetic pathways were ablated. These results indicate that ghrelin applied centrally or peripherally markedly increases resistance of the intestinal tissue during the I/R period induced mucosal and hyperemic impairment evoked by I/R. Ghrelin is an important mediator of the increase in the intestinal microcirculation and elevation of the intestinal metabolism, which seems to be, at least in part, responsible for the observed protection of the intestine subjected to I/R. Impairment of this microvasculature response due to I/R seems to be responsible for a markedly observed weaker effect of ghrelin when this hormone was administered after the ischemic period. The lack of a protective effect observed after central administration of this peptide against a long lasting I/R period is probably due to damage of neural pathways caused by I/R. Finally, the peripheral activity of ghrelin in the intestine is mediated by the sensory neurons with a prominent role of CGRP released from their endings. However, this peripheral action of ghrelin depends upon the proper functioning of both the sympathetic and parasympathetic system.

Arterial thrombosis: relevance of a model with two levels of severity assessed by histologic, ultrastructural and functional characterization

BACKGROUND

We previously described a model of laser-induced thrombosis in mesenteric arterioles with superficial and deep levels of injury producing a transient thrombus resolving within 2 min and a larger almost occlusive thrombus, respectively. Both types of lesion were sensitive to platelet GPIIb-IIIa and P2Y(12) inhibition, whereas only deep injuries were sensitive to thrombin blockade.

OBJECTIVE

The aim of the present study was to use histologic methods and electron and intravital microscopy to characterize the lesions and thrombi and to extend our knowledge of the sensitivity of this model to genetic and pharmacologic inhibition.

RESULTS

A superficial injury was found to detach the endothelial cells and expose a collagen III- and IV-rich subendothelium where platelets could adhere. Tissue factor and fibrin were not detected. Deeper penetration of the external elastic lamina occurred in deep injuries, with exposure of collagen I, III and IV. Here the thrombus was composed of platelets exhibiting a decreasing gradient of degranulation from the deepest lesion area to the surface. Fibrin was found close to the most activated platelets. Consistently, glycoprotein VI (GPVI)-collagen and GPIb-von Willebrand factor (VWF) interactions were found to be critical in superficial injuries. After deep lesion, thrombus formation was modestly reduced in GPVI-immunodepleted mice and still strongly inhibited in VWF(-/-) mice. Combined hirudin infusion and GPVI depletion further inhibited thrombosis after deep injury.

CONCLUSIONS

This study confirms the feasibility of inducing arterial thrombosis with distinct levels of severity and establishes the central roles of collagen and VWF in thrombus formation after superficial injury. Collagen, VWF and thrombin all appear to contribute to thrombosis after deep arterial lesion.

[Portal vein thrombosis after laparoscopy--an underestimated complication]

Portal vein thrombosis after laparoscopy became an issue of interest with the technological progress in surgery (the expanding use of minimally invasive approach) and imaging (the higher availability of Doppler ultrasonography and spiral computer tomography). Along with the extensive interest for laparoscopy in our country, a guideline for the prophylaxis and treatment of this potentially deadly complication seems necessary. Portal vein thrombosis (PVT) should be promptly diagnosed and treated to prevent its extension to the superior mesenteric venous system, as it may sometime trigger a potentially life-threatening complication, the entero-mesenteric venous infarction. It is acknowledged that the increasing use of laparoscopy in the last decades represents a major therapeutical progress. The effects of this approach are still to be explored.

Replanting the inferior mesentery artery during infrarenal aortic aneurysm repair: influence on postoperative colon ischemia

BACKGROUND

Replanting the inferior mesentery artery (IMA) to prevent ischemic colitis (IC) has been discussed for many years; yet, to our knowledge, no prospective studies have been conducted to compare the incidence of histologically proven IC in patients with and without IMA revascularization. The aim of this prospective study, with histologic evaluation of the sigmoid colon mucosa, was to assess the influence of replanting the IMA on IC and mortality.

METHODS

From January 1999 to December 2003, 160 consecutive patients who were operated on for a symptomatic (n = 21) or asymptomatic (n = 139) infrarenal aortic aneurysm were prospectively assessed and randomly assigned either to replanting or ligating the IMA. Sigmoidoscopy with biopsy was performed on day 4 or 5 after surgery; an autopsy was performed on patients not surviving to day 5 after surgery. All patients gave written informed consent.

RESULTS

Of the 160 randomized patients, 128 had a confirmed patent IMA and formed the basis of this study. Their age was 70 +/- 8 years (men, 70 +/- 8 years; women, 73 +/- 7 years). The IMA was replanted in 67 patients (52%) and ligated in 61 (48%) intraoperatively. IC developed in six patients with a replanted IMA and in 10 with a ligated IMA (relative risk [RR], 0.55; 95% confidence interval [CI], 0.21 to 1.41; chi2 = 1.62; P = .203). Blood loss in the two cohorts did not differ significantly (P = .788); however, patients with IC had a significantly higher blood loss compared with the cohort without IC (P = .012) and were older (P = .017). Age, sex distribution, clamping time, the use of tube or bifurcated grafts, and intraoperative hypotension did not differ between patients with ligated or replanted IMA.

CONCLUSION

Although replanting the IMA did not confer a statistically significant reduction of perioperative morbidity or mortality in this study, it appears that older patients and patients with increased intraoperative blood loss might benefit from IMA replantation, because this maneuver does not increase perioperative morbidity or substantially increase operation time.

Acute mesenteric ischemia: still high mortality rate in the era of 24-hour availability of angiography

BACKGROUND

Acute mesenteric ischemia (AMI) is a serious condition with high mortality rate due to difficult and late diagnosis. Early and aggressive evaluation in high risk patients by mesenteric angiography is the key to the reduction in mortality rate. However; many physicians hesitated to perform it because of its availability, the risk of complications and high negative results. This study reviewed outcome of AMI in term of mortality rate, factors associated with mortality and the rate of angiography in high risk patients.

MATERIAL AND METHOD

The clinical data of the patients who were diagnosed as AMI were retrospectively reviewed. The clinical outcome was recorded and the factors associated with mortality were analysed.

RESULTS

Thirty-five patients were enrolled into this study during 5 years. The mortality rate was 74.3%. There were 22 high risk patients for AMI. The rate of angiography performed in this group was 4.5% (1/22). The factors associated with mortality were age more than 60 years, patients with peritonitis, hypotension, arterial cause, time interval between admission and operation or treatment more than 24 hours, bowel gangrene >100 cms. However all these factors were not statistically significant.

CONCLUSION

The mortality rate of AMI is still high even at the tertiary hospital where the angiography is available 24 hours. To decrease the mortality rate, the physicians must have the high index of suspicion in high risk patients and do not hesitate to perform early mesenteric angiography.

Inhibitory activity of kinetin on free radical formation of activated platelets in vitro and on thrombus formation in vivo

Kinetin has been shown to have anti-aging effects on several different systems, including plants and human cells. Recently, we demonstrated that kinetin markedly inhibited platelet aggregation in washed human platelets. In the present study, an electron spin resonance (ESR) method was used to further evaluate the scavenging activity of kinetin on the free radicals formed. Kinetin (70 and 150 microM) concentration dependently reduced the ESR signal intensity of hydroxyl radicals in collagen (1 microg/ml)-activated platelets. Furthermore, kinetin was effective in reducing the mortality of ADP-induced acute pulmonary thromboembolism in mice when administered intravenously at doses of 4 and 6 mg/kg. In addition, intravenous injection of kinetin (4 and 6 mg/kg) significantly prolonged the bleeding time by approximately 1.9- and 2.1-fold as compared with normal saline in severed mesenteric arteries of rats. A continuous infusion of kinetin (0.6 mg/kg/min) for 10 min also significantly increased the bleeding time by about 2.3-fold, and the bleeding time returned to baseline within 120 min after cessation of kinetin infusion. Platelet thrombi formation was induced by irradiation of mesenteric venules with filtered light in mice pretreated intravenously with fluorescein sodium. When kinetin was administered at 13 and 14 mg/kg in mice pretreated with fluorescein sodium (5 mg/kg), the occlusion time was significantly prolonged. In conclusion, these results suggest that kinetin has effective free radical-scavenging activity in vitro and antithrombotic activity in vivo. Treatment with kinetin may lower the risk of thromboembolic-related disorders. Therefore, kinetin may be a potential therapeutic agent for arterial thrombosis, but its toxicity must be further assessed.

[The possible role of NO in regulating the thrombogenic and thromboresistant properties of the vessels in cerebral ischemia and postischemic reperfusion in rats]

In rats weighing 200 to 250 g, postischemic reperfusion of the brain induced distant alterations in the microvessel thromboresistance. A significant decrease in the venule thrombogenesis properties occurred. Changes found in the arterioles may be assessed as an increase of the haemostatic potential.

Lipocortin 1 protects against splanchnic artery occlusion and reperfusion injury by affecting neutrophil migration

Splanchnic artery occlusion and reperfusion (SAO/R) shock was induced in rats by clamping both the superior mesenteric artery and the celiac trunk for 45 min, followed by release of the clamp (60-min reperfusion). Following this reperfusion period, rats developed a fall in mean arterial blood pressure, associated with a significant increase in tissue myeloperoxidase (MPO) activity in the intestine and a marked histologic injury to the distal ileum. Treatment of rats with a lipocortin-1 (LC1)-derived N-terminal peptide, peptide Ac(2-26), dose-dependently (0.125-0.5 mg/kg s.c.) reduced the progressive fall in blood pressure and prevented the infiltration of neutrophils into the reperfused intestine (reduced MPO activity). The LC1 peptide also reduced the degree of ischemia/reperfusion injury in the bowel as evaluated by histologic examination. The glucocorticoid dexamethasone (0.1 mg/kg s.c., -1 h) also produced a marked improvement in SAO/R shock (i.e., maintained mean arterial blood pressure and reduced tissue MPO activity), and this was reversed by pretreatment with two different antisera raised against the LC1 pharmacophore. Peptide Ac(2-26) (0.5 mg/kg s.c., -30 min) reduced (>60%) the extent of IL-1beta-induced cell emigration and significantly attenuated (approximately 45%) the number of adherent leukocytes in the rat mesenteric vascular bed, as assessed by video microscopy. These results suggest that LC1 inhibits neutrophil migration and accumulation into reperfused tissues, thereby ameliorating the outcome of SAO/R shock.

[Role of coagulation disorders in mesenteric ischemia]

Mesenteric ischemic process can lead to bowel infarction or indolent low-grade ischemia. Inherited thrombophilia represents about 30 to 40% of mesenteric vein thrombosis. Analysis of thromboembolism sites occurring during genetic defect of coagulant factors showed that mesenteric thrombosis is the third localization after lung and legs, in equal incidence with cerebral thrombosis. The genetic defects known to be associated with thrombophilia, as deficiencies of protein C, protein S, antithrombin III, and dysfibrinogenemia, are discussed. A special interest is devoted to resistance to activated protein C. Acquired diseases, as myeloproliferative disease or paroxysmal nocturnal hemoglobinemia, inducing thrombosis are also discussed. Recent advances in both basic and clinical research have provided new insights that may be integrated into diagnostic and therapeutic practices.

Effect of troxerutin on laser-induced thrombus formation in rat mesenteric vessels, coagulation parameters and platelet function

The antithrombotic effect of Troxerutin have been studied in an experimental model of thrombosis in which rat mesenteric vessels (arterioles and venules) 25-30 microns in diameter were injured by well defined argon laser lesions. Furthermore in vitro effect of this agent on coagulation parameters (IIa, Xa inhibition, TT, heptest), and platelet function (platelet adhesion to the siliconised glass and extracellular matrix, platelet spreading) has been investigated 2 h after oral drug administration. Troxerutin at a dose of 10 mg/kg markedly inhibited thrombus formation in venules. Higher dose (50 mg/kg) was needed to obtain the same antithrombotic effect when arterioles were studied. After application of a single dose of Troxerutin (100 mg/kg) antithrombotic effect lasted for 6 h to 7.5 h when venules were studied, and for 4.5 h to 6 h when arterioles were investigated. In in vitro study we did not observe any effect of Troxerutin on coagulation parameters. In concentrations of 100 micrograms/ml in platelet rich plasma Troxerutin significantly inhibited platelet adhesion to the extracellular matrix and siliconised glass as well as platelet spreading. It is likely that this drug possesses antithrombotic effect evaluated by inhibition of platelet function and protection of endothelial cells.

Experimental thrombosis model induced by free radicals. Application to aspirin and other different substances

A large number of experimental studies suggests that oxygen free radicals play a major role in the pathogenesis of the myocardial lesions observed during the sequence ischemia-reperfusion. The purpose of this study was to determine whether oxygen free radicals can induce thrombosis. In so doing we have developed a new experimental thrombosis model. Reproducible focal thrombosis has been achieved by irradiating mesenteric arterioles of rat for variable time with green filtered light issuing from a mercury lamp after systemic injection of different rose bengal doses. The number of emboli that remove in the blood (N), the duration of total occlusion (T) and the number of emboli per minute were then measured. As control, no rose bengal administration was done and the vessels were exposed to the filtered light. In comparison with this control, results clearly showed that free radicals always induced thrombosis and the induced thrombus was mainly composed of platelets. In this new thrombosis model induced by free radicals antithrombotic drugs (aspirin, 200 mg/Kg, heparin, 2 mg/Kg) and antioxidants (vitamin C, 10 and 20 mg/Kg, allopurinol, 200 and 300 mg/Kg, vitamin E, 500 and 1000 mg/Kg) have been tested. Results have shown that only heparin and vitamin E had an antithrombotic effect on thrombus formation induced by free radicals. This model should be useful in studying the effects of different drugs and could lead to new treatment modalities for ischemic accident and other cardiovascular diseases.

Antithrombotic activity of a symmetrical triglyceride with eicosapentaenoic acid and gamma-linolenic acid in guinea pig mesenteric microvasculature

The antithrombotic effect of a synthetic symmetrical triglyceride having eicosapentaenoic acid (EPA) at positions 1 and 3, and gamma-linolenic acid (GLA) at position 2 was investigated. Administration of the triglyceride significantly increased thrombus formation time and thrombotic occlusion time induced by light irradiation and a fluorescent dye in guinea pigs after 14 days administration compared to that of soybean oil. The antithrombotic effect of the triglyceride was similar to that of EPA ethyl ester. Administration of the triglyceride increased GLA, dihomo-gamma-linolenic acid (DGLA) and EPA contents in plasma and the liver, and the ratio of DGLA to arachidonic acid. These results might be responsible for this antithrombotic effect.

A new technique for early detection of portal vein and arterial thromboses. Indwelling mesenteric venous catheterization and relevance to small bowel transplantation

The aim of this study was to ascertain whether, in an animal model, continuous monitoring of mesenteric venous pressure (MVP) via an indwelling mesenteric venous catheter could assist in early detection of thrombosis of the portal vein (PVT) and superior mesenteric artery (SMAT). The role of portography via the catheter was also studied in confirming these complications. An animal model of PVT and SMAT was developed in pigs. At laparotomy, a 20-cm jejunal loop was isolated and a heparin-coated catheter was inserted into a mesenteric vein of the isolated jejunum and connected to a pressure transducer. Conditions of PVT were simulated by progressive occlusion of the portal vein (PV) using a silastic tourniquet and those of SMAT by superior mesenteric artery (SMA) clamping. MVPs (mm Hg) were found to significantly increase with all degrees of PV occlusion (P < 0.01, Student's t test) and to significantly decrease after SMA occlusion (P < 0.01). Portography clearly demonstrated all degrees of PV stenosis after PV occlusion and stasis of contrast medium during SMA occlusion. The authors feel that this method enables rapid diagnosis of PVT and SMAT and may be useful in the monitoring of the therapy for these complications after small bowel transplantation.

Concept of an antiatherosclerotic efficacy of calcium entry blockers. INTACT Investigators

Animal experiments suggest an inhibitory effect of calcium entry blockers on arterial calcinosis and the formation of atherosclerotic plaques. Experiments with isolated tissues suggest various mechanisms for an antiatherosclerotic effect of calcium entry blockers. INTACT, the International Nifedipine Trial on Antiatherosclerotic Therapy, is the first study investigating, with a prospective, placebo-controlled, randomized, double-blind design, the influence of a calcium entry blocker (nifedipine 80 mg/day) on the progression of coronary atherosclerosis in patients with proven coronary artery disease. Study endpoints were changes of established coronary stenoses (diameter reduction greater than or equal to 20%), as well as the formation of new stenoses as documented by coronary angiography. Standardized coronary angiograms were taken before and after a treatment period of 3 years. The angiograms were quantitatively analyzed with the computer-assisted edge detection system CAAS. Of the 425 patients included in the study, 282 patients (134 on nifedipine and 148 on placebo) revealed no protocol violations. In the inclusion angiograms of these patients, 893 coronary stenoses were detected which were not significantly influenced in their development by nifedipine. However, 196 entirely new coronary lesions, 185 stenoses and 11 occlusions, were found in the follow-up angiograms. There were 78 lesions in 54 patients (40%) on nifedipine (0.58 new lesions/patient) and 118 lesions in 73 patients (49%; n.s.) on placebo (0.8 new lesions/patient; p = 0.031). In two other studies on the inhibiting effect of dihydropyridine calcium entry blockers on the progression of coronary artery disease in man defining angiographic endpoints, the drugs were also shown to reduce the number of newly formed significant coronary lesions. If further trials in man confirm a protective role of calcium entry blockers against the formation of atherosclerotic coronary lesions, a new strategy in the prevention of coronary artery disease has to be considered.

Inhibitory effects of mold oil including gamma-linolenate on platelet thrombus formation in mesenteric microvessels of the rat

Diet including mold oil from a lipid accumulative fungus, containing gamma-linolenic acid, showed an inhibitory effect on thrombus formation in the microvessels of rats by the light/dye method of the authors. Male Wistar rats were fed for 3 to 4 weeks with two series of experimental diets and were examined for thrombus formation. The thrombus formation times to totally occlude, ts, were 347 sec for (mold + soybean)-oil and 236 sec for (palm + soybean)-oil in the first series of diets and 1288 sec for mold oil, 538 sec for olive oil and 575 sec for safflower oil in the second series of diets. Fatty acid composition of plasma, erythrocyte and liver lipids showed an increase in arachidonate content with the diet including the mold oil. Higher arachidonate content seem favorable in inhibiting thrombus formation with increasing PGI2 formation. In terms of the level of lipid hydroperoxides, indicated as a desaturation index of constituent fatty acids, the higher desaturation index with safflower oil gave shorter ts, which suggested some oxygen derived free radicals from polyunsaturated fatty acids were involved in the mechanism of thrombogenesis study by this method.

[Inhibition of the formation of platelet thrombus by molsidomine and SIN-1 in the mesenteric vessels rats]

Molsidomine and SIN-1 were tested in a thrombosis model in which thrombi are produced in small mesenteric vessels. An interference contrast system based on a Leitz Orthoplan microscope was used to visualize thrombus formation. Vascular lesions were produced with a Coherent CR-Z supergraphite ion laser (Argon laser) in vessel of 20-30 micron diameter. Molsidomine and SIN-1 i.v. at doses of 0.1 and 0.5 mg/kg had a marked and significant antithrombotic effect in arterioles and in venules. Molsidomine at doses of 0.1 and 0.5 mg/kg had no antithrombotic effect 90 min following intravenous injection.

Effect of a prostaglandin E1 derivative (OP-1206) and acetylsalicylic acid on electrically induced thrombosis in guinea-pig mesenteric artery and its modification by an inhibitor of prostaglandin I2 synthetase, tranylcypromine

The antithrombotic effect of a prostaglandin E1 derivative, OP-1206 (17S-20-dimethyl-trans-delta 2-PGE1) X alpha-cyclodextrin clathrate (OP-1206 X alpha-CD), was compared with that of acetylsalicylic acid (ASA) in a electrically induced thrombosis model of guinea-pig mesenteric arteries using intact animals and animals subjected to the superfusion of tranylcypromine (TC, 15 mM) over their mesentery. The drug-effect was assessed by the change of the threshold voltage for the thrombus formation. 1) TC (1.5-15 mM) lowered the threshold voltage, and the effect was comparable to its inhibitory effect on PGI2 formation in vitro, suggesting that PGI2 generated in mesenteric arteries acts to prevent thrombus formation. 2) In intact animals, OP-1206 X alpha-CD at doses of 0.01-0.3 mg/kg, p.o. (as OP-1206), significantly and dose-dependently elevated the threshold voltage. ASA (30-1000 mg/kg, p.o.) significantly elevated the threshold voltage, but the effect reached to its maximum at 100 mg/kg and lessened with further increase of ASA. 3) In TC-treated animals, OP-1206 X alpha-CD elevated the threshold voltage dose-dependently, but the elevation of threshold voltage by ASA reached to its plateau level which was significantly lower than that obtained with OP-1206 X alpha-CD at 0.3 mg/kg, indicating that the antithrombotic effect of ASA is incomplete in this model.(ABSTRACT TRUNCATED AT 250 WORDS)

Concomitant revascularization of intestines during aortoiliac reconstruction: deterrent to catastrophic bowel infarction

This report points out the necessity for revascularization of the intestines in patients with asymptomatic mesenteric occlusive disease at the time of aortoiliac reconstruction. Emphasis is placed upon the well-being of 15 patients followed up for 2 to 5 years, who underwent concomitant bypass grafting of asymptomatic stenosis or occlusion of the mesenteric arteries, in contrast to the fatal or near fatal outcome of 3 patients who did not receive such corrective measures. Aortomesenteric bypass grafting in conjunction with aortobifemoral bypass grafting or endarterectomy does not involve additional operative exposure or add greatly to the operating time, but may prevent catastrophic bowel infarction resulting from progressive occlusion of the mesenteric arteries.