Sarcoplasmic reticulum and excitation-contraction coupling in mammalian smooth muscles

The sarcoplasmic reticulum (SR) was studied in the smooth muscles of rabbit main pulmonary artery, mesenteric vein, aorta, mesenteric artery, taenia coli, guinea pig mesenteric artery, and human uterus, and correlated with contractions of the smooth muscles in Ca-free media. SR volumes were determined in main pulmonary artery (5.1%), aorta (5%), portal-anterior mesenteric vein (2.2%), taenia coli (2%), and mesenteric artery (1.8%): because of tangentially sectioned membranes these estimates are subject to a correction factor of up to +50% of the values measured. Smooth muscles that contained a relatively large volume of SR maintained significant contractile responses to drugs in the virtual absence of extracellular calcium at room temperatures, while smooth muscles that had less SR did not. The unequal maximal contractions of main pulmonary artery elicited by different drugs were also observed in Ca-free, high potassium-depolarizing solution, indicating that they were secondary to some mechanism independent of changes in membrane potential or calcium influx. Longitudinal tubules of SR run between and are fenestrated about groups of surface vesicles separated from each other by intervening dense bodies. Extracellular markers (ferritin and lanthanum) entered the surface vesicles, but not the SR. The peripheral SR formed couplings with the surface membrane: the two membranes were separated by gaps of approximately 10 nm traversed by electron-opaque connections suggestive of a periodicity of approximately 20-25 nm. These couplings are considered to be the probable sites of electromechanical coupling in twitch smooth muscles. Close contacts between the SR and the surface vesicles may have a similar function, or represent sites of calcium extrusion. The presence of both thick and thin myofilaments and of rough SR in smooth muscles supports the dual, contractile and morphogenetic, function of smooth muscle.

Recent portal or mesenteric venous thrombosis: increased recognition and frequent recanalization on anticoagulant therapy

Characteristics and outcomes of recent portal or mesenteric venous thrombosis are ill-known. We intended to compare these features with those of patients with portal cavernoma, and also to assess the incidence of recanalization of recent thrombosis on anticoagulation therapy. All patients seen between 1983 and 1999 were enrolled into this retrospective study if recent portal or mesenteric venous thrombosis or portal cavernoma had been documented, and if cancer of the liver, pancreas, or bile duct, intrahepatic block including cirrhosis, and obstruction of the hepatic veins had been ruled out. The proportion of recent thrombosis was 7% in patients seen before 1990 and 56% after 1994 (P <.05). Patients with recent thrombosis (n = 33) or cavernoma (n = 108) did not differ with regard to age, sex ratio, or prevalence of prothrombotic states and of previous thrombotic events. In patients with recent thrombosis, septic pylephlebitis was more common and the incidence of gastrointestinal bleeding was lower (2.4 vs. 12.7/100 patient-years). Recanalization occurred in 25 of 27 patients given anticoagulation and 0 of 2 patients not given anticoagulation. The probability of recanalization was related to the extent of thrombosis (P =.003). In conclusion, mesenteric or portal venous thrombosis is increasingly recognized at an early stage. The features differentiating recent thrombosis and cavernoma are related to silent onset precluding early recognition and therapy in the latter. Frequent association with prothrombotic states and frequent recanalization on anticoagulation support the recommendation of early anticoagulation therapy in all patients with recent portal vein thrombosis.

PULSATILE PRESSURES IN THE MICROCIRCULATION OF FROG'S MESENTERY

Pressure within the microvascular bed of the frog mesentery has been recorded continuously with micropressure transducers which have tip diameters ranging between 0.5–5 µ. The mean values of pressure are in the range of those previously reported. The waveform of the pressure pulses in arterioles and metarterioles closely resembles that in the larger arteries. This observation signifies that the vascular walls are considerably stiffer than is generally believed. The stiffness is probably attributable to the constricted vascular smooth muscle.

Systematic review of survival after acute mesenteric ischaemia according to disease aetiology

BACKGROUND

Differentiation of acute mesenteric ischaemia on the basis of aetiology is of great importance because of variation in disease progression, response to treatment and outcome. The aim of this study was to analyse the published data on survival following acute mesenteric ischaemia over the past four decades in relation to disease aetiology and mode of treatment.

METHOD

A systematic review of the available literature from 1966 to 2002 was performed.

RESULTS

Quantitative analysis of data derived from 45 observational studies containing 3692 patients with acute mesenteric ischaemia showed that the prognosis after acute mesenteric venous thrombosis is better than that following acute arterial mesenteric ischaemia; the prognosis after mesenteric arterial embolism is better than that after arterial thrombosis or non-occlusive ischaemia; the mortality rate following surgical treatment of arterial embolism and venous thrombosis (54.1 and 32.1 per cent respectively) is less than that after surgery for arterial thrombosis and non-occlusive ischaemia (77.4 and 72.7 per cent respectively); and the overall survival after acute mesenteric ischaemia has improved over the past four decades.

CONCLUSION

There are large differences in prognosis after acute mesenteric ischaemia depending on aetiology. Surgical treatment of arterial embolism has improved outcome whereas the mortality rate following surgery for arterial thrombosis and non-occlusive ischaemia remains poor.

Quantitative investigations of the adhesiveness of circulating polymorphonuclear leucocytes to blood vessel walls

1. A new simple method is described for quantitating the adhesiveness of circulating polymorphonuclear leucocytes, or granulocytes, to the walls of blood vessels. The cheek pouch of anaesthetized hamsters or a small part of the mesentery of anaesthetized mice were prepared for continuous microscopic observation of selected venules. Those granulocytes which moved sufficiently slowly to be individually visible were counted for 1 or 2 min periods as they rolled past a selected point on one side of a vessel. The velocity distribution of these cells was determined by analysing films. Films were used also to measure mean blood flow velocity in the venules by observing embolizing platelet thrombi induced by the iontophoretic application of adenosine diphosphate. Emigration of granulocytes into the tissues was quantitated by enumerating them in standard areas of stained histological sections.2. In control experiments with hamster cheek pouch venules, the rolling granulocyte count usually passed through a maximum shortly after the preparation was set up and then fell to a low constant value. In mouse mesentery venules the count remained at a low approximately constant value from the beginning for at least 3 hr.3. The mean velocity of blood flow in the venules was between 900 and 200 mu/sec. All rolling granulocytes moved much more slowly; in hamster cheek pouch venules the mean velocity was about 20 mu/sec and in mouse mesentery venules about 10 mu/sec. Around these means the velocity distribution of individual cells was narrow.4. Rolling of granulocytes was abolished by superfusing ethylenediamine tetra-acetate (EDTA, 0.1 M) suggesting that the phenomenon depends on calcium or magnesium ions.5. Agents were applied locally to the observed venules. Human serum albumin, trypsin or histamine in high concentrations did not affect the rolling granulocyte count.6. The rolling granulocyte count was increased during the application of Hammarsten casein or Escherichia coli culture filtrate which are chemotactic to granulocytes in vitro. These agents did not cause alterations in mean blood flow velocity in the observed venules which might have accounted for the effect on the rolling granulocyte counts. When E. coli culture filtrate was perfused through mouse intestine the increase in rolling granulocyte count in the draining venous blood was proportional to the logarithm of the concentration of filtrate.7. The rolling granulocyte count was also increased by the local application of plasma globulin permeability factor or lymph node permeability factor.8. Granulocyte counts in standard histological sections showed no significant increases in control preparations but considerable increases following the application of Hammarsten casein.

Pneumatosis intestinalis and portomesenteric venous gas in intestinal ischemia: correlation of CT findings with severity of ischemia and clinical outcome

OBJECTIVE

The purpose of this study was to analyze the correlation between pneumatosis or portomesenteric venous gas, or both, the severity of mural involvement, and the clinical outcome in patients with small- or large-bowel ischemia.

MATERIALS AND METHODS

CT scans of 23 consecutive patients presenting with pneumatosis or portomesenteric venous gas caused by bowel ischemia were reviewed. The presence and extent of both CT findings were compared with the clinical outcome in all patients and with the severity and extent of ischemic bowel wall damage as determined by surgery (15 patients), autopsy (three patients), or follow-up (five patients).

RESULTS

Seven patients showed isolated pneumatosis, and 16 patients showed portomesenteric venous gas with or without pneumatosis (11 and five patients, respectively). Pneumatosis and portomesenteric venous gas were associated with transmural bowel infarction in 14 (78%) of 18 patients and 13 (81%) of 16 patients, respectively. Nine patients (56%) with portomesenteric venous gas died. Of seven patients with infarction limited to one bowel segment (jejunum, ileum, or colon), only one patient (14%) died, whereas of the 10 patients with infarction of two or three bowel segments, eight patients (80%) died.

CONCLUSION

CT findings of pneumatosis intestinalis and portomesenteric venous gas due to bowel ischemia do not generally allow prediction of transmural bowel infarction, because they may be observed in patients with only partial ischemic bowel wall damage. The clinical outcome of patients with bowel ischemia with these CT findings seems to depend mainly on the severity and extent of their underlying disease.

Correlation between spiral computed tomography, endoscopic ultrasonography and findings at operation in pancreatic and ampullary tumours

BACKGROUND

Spiral computed tomography (CT) allows high-resolution examination of the pancreas, surrounding vascular structures, lymph nodes and liver. Endoscopic ultrasonography (EUS) also allows high-resolution imaging of the pancreas and adjacent structures but is an invasive procedure. With the availability of spiral CT, the role of EUS in the investigation of patients with suspected pancreatic or ampullary tumours is unclear.

METHODS

Forty-eight patients with clinical suspicion of a pancreatic or ampullary tumour underwent both spiral CT and EUS. Thirty-four patients had surgical exploration, of whom 17 underwent pancreatic resection and 17 had biliary and gastric bypass. The results of spiral CT and EUS were compared with the operative findings.

RESULTS

The final histological diagnosis was ductal adenocarcinoma (24 patients), ampullary carcinoma (six), serous cystadenoma (two) and chronic pancreatitis (two). EUS demonstrated 33 and spiral CT 26 of the 34 primary lesions. EUS was particularly useful in the assessment of small resectable tumours missed by spiral CT. The sensitivity and specificity of EUS and spiral CT for detecting involvement by the tumour of the superior mesenteric vein, portal vein and lymph nodes were similar, but EUS was less effective at evaluating the superior mesenteric artery.

CONCLUSION

EUS is an important additional investigation after spiral CT in patients with a suspected pancreatic or ampullary tumour.

Septic thrombophlebitis of the portal vein (pylephlebitis): diagnosis and management in the modern era

Pylephlebitis usually occurs secondary to infection in the region drained by the portal venous system. We describe a case of pylephlebitis at our institution and examine 18 other cases culled from the literature since 1979, reviewing diagnostic and management issues. A precipitating focus of infection (most commonly diverticulitis) was identified in 13 (68%) of the cases. Bacteremia (often polymicrobial) was present in 88% of the patients. The most common blood isolate was Bacteroides fragilis. Overall mortality was 32%, but most of the patients who died had severe sepsis prior to the initiation of antibiotic therapy. In no case was improvement in a patient's clinical status clearly attributable to the use of heparin, but some beneficial effect of anticoagulation could not be ruled out. This report is the first to examine the published experience with pylephlebitis during the era of antibiotics and modern imaging and is also the first to review critically the role of anticoagulation in the management of this disease.

Role of CD11/CD18 in shear rate-dependent leukocyte-endothelial cell interactions in cat mesenteric venules

In vivo microscopy was used to assess the relationships among shear rate (and shear stress), leukocyte rolling velocity, and leukocyte adherence in a cat mesentery preparation. Shear rate in individual venules and arterioles of 25-35 microns diameter were varied over a wide range by graded occlusion of an arterial loop. There was a linear decline in leukocyte rolling velocity (Vwbc) as red cell velocity (Vrbc) was reduced. The ratio Vwbc/Vrbc remained constant despite variations in shear stress from 5-25 dyn/cm2. A reduction in shear stress was associated with an increased leukocyte adherence, particularly when Vwbc was reduced below 50 microns/s. Reduction in wall shear rate below 500 s-1 in arterioles allowed 1-3 leukocytes to adhere per 100 microns length of vessel, while venules exposed to the same shear rates had 5-16 adherent leukocytes. In arterioles, leukocyte rolling was only observed at low shear rates. At shear rates less than 250 s-1 leukocyte rolling velocity was faster in arterioles than venules, and the ratio Vwbc/Vrbc for arterioles was 0.08 +/- 0.02, which was fourfold higher than the ratio obtained in venules at similar shear rates. Pretreatment with the CD18-specific antibody (mAb) IB4 increased leukocyte rolling velocity in venules by approximately 20 microns/s at red cell velocities below 2,000 microns/s. mAb IB4 largely prevented the leukocyte adherence to arterioles and venules, and increased the ratio Vwbc/Vrbc observed in venules at low shear elicit a CD18-dependent adhesive interaction between leukocytes and microvascular endothelium, and that differences in shear rates cannot explain the greater propensity for leukocyte rolling and adhesion in venules than arterioles.

Acute mesenteric ischemia: the challenge of gastroenterology

Intestinal ischemia has been classified into three major categories based on its clinical features, namely, acute mesenteric ischemia (AMI), chronic mesenteric ischemia (intestinal angina), and colonic ischemia (ischemic colitis). Acute mesenteric ischemia is not an isolated clinical entity, but a complex of diseases, including acute mesenteric arterial embolus and thrombus, mesenteric venous thrombus, and nonocclusive mesenteric ischemia (NOMI). These diseases have common clinical features caused by impaired blood perfusion to the intestine, bacterial translocation, and systemic inflammatory response syndrome. Reperfusion injury, which exacerbates the ischemic damage of the intestinal microcirculation, is another important feature of AMI. There is substantial evidence that the mortality associated with AMI varies according to its cause. Nonocclusive mesenteric ischemia is the most lethal form of AMI because of the poor understanding of its pathophysiology and its mild and nonspecific symptoms, which often delay its diagnosis. Mesenteric venous thrombosis is much less lethal than acute thromboembolism of the superior mesenteric artery and NOMI. We present an overview of the current understanding of AMI based on reported evidence. Although AMI is still lethal and in-hospital mortality rates have remained high over the last few decades, accumulated knowledge on this condition is expected to improve its prognosis.

Catechin is metabolized by both the small intestine and liver of rats

Flavan-3-ols are the most abundant flavonoids in the human diet, but little is known about their absorption and metabolism. In this study, the absorption and metabolism of the monomeric flavan-3-ol, catechin, was investigated after the in situ perfusion of the jejunum + ileum in rats. Five concentrations of catechin were studied, ranging from 1 to 100 micromol/L. The absorption of catechin was directly proportional to the concentration, and 35 +/- 2% of the perfused catechin was absorbed during the 30-min period. Effluent samples contained only native catechin, indicating that intestinal excretion of metabolites is not a mechanism of catechin elimination. Catechin was absorbed into intestinal cells and metabolized extensively because no native catechin could be detected in plasma from the mesenteric vein. Mesenteric plasma contained glucuronide conjugates of catechin and 3'-O-methyl catechin (3'OMC), indicating the intestinal origin of these conjugates. Additional methylation and sulfation occurred in the liver, and glucuronide + sulfate conjugates of 3'OMC were excreted extensively in bile. Circulating forms were mainly glucuronide conjugates of catechin and 3'OMC. The data further demonstrate the role of the rat small intestine in the glucuronidation and methylation of flavonoids as well as the role of the liver in sulfation, methylation and biliary excretion.

Mesenteric venous thrombosis: a changing clinical entity

OBJECTIVE

Mesenteric venous thrombosis (MVT) and its clinical spectrum have become better defined following improvements in diagnostic imaging. Historically, MVT has been described as a morbid clinical entity, but this may not necessarily be true. Often, an underlying disease process that predisposes a patient to MVT can be found and potentially treated. This study was designed to evaluate the diagnostics and management of MVT and to review long-term results of treatment.

PATIENTS

Thirty-one patients in whom MVT was diagnosed between 1985 and 1999 were retrospectively reviewed. Survivors were contacted for follow-up. There were 15 men and 16 women. Ages ranged from 22 to 80 years (mean, 49.1 years). Thirteen patients had documented hypercoagulability, 10 had a history of previous abdominal surgery, 6 had a prior thrombotic episode, and 4 had a history of cancer. MVT presented as abdominal pain (84%), diarrhea (42%), and nausea/vomiting (32%). Computed tomography (CT) was considered diagnostic in 18 (90%) of 20 patients who underwent the test. CT diagnosed MVT in 15 (100%) of 15 patients presenting with vague abdominal pain or diarrhea. Angiography demonstrated MVT in only five (55.5%) of nine patients.

RESULTS

Seven of 31 patients died within 30 days (< 30-day mortality rate, 23%). Twenty-two patients (72%) were initially treated with heparin. Nine patients were not heparinized: four of them died, and two were later given warfarin sodium (Coumadin). Of the 31 patients, only one received lytic therapy. Three patients became symptom free without anticoagulation. Ten patients (32%) underwent bowel resection. Overall, 19 (79%) of 24 survivors were treated with long-term warfarin therapy. Long-term follow-up was obtained in 24 patients (mean, 57.7 months). Twenty-one (88%) of 24 survived in follow-up.

CONCLUSION

The diagnosis of MVT should be suspected when acute abdominal symptoms develop in patients with prior thrombotic episodes or a documented coagulopathy. CT scanning appears to be the primary diagnostic test of choice. Anticoagulation is recommended. If diagnosed and treated early, MVT is not likely to progress to gangrenous bowel. Recent mortality rates for MVT are lower than previously published, perhaps because of earlier diagnosis and aggressive treatment or possibly because we now readily diagnose a more benign form of the disease, which is due to widespread use of CT scanning.

Sweet talk in the brain: glucosensing, neural networks, and hypoglycemic counterregulation

Glucose is the primary fuel for the vast majority of cells, and animals have evolved essential cellular, autonomic, endocrine, and behavioral measures to counteract both hypo- and hyperglycemia. A central component of these counterregulatory mechanisms is the ability of specific sensory elements to detect changes in blood glucose and then use that information to produce appropriate counterregulatory responses. Here we focus on the organization of the neural systems that are engaged by glucosensing mechanisms when blood glucose concentrations fall to levels that pose a physiological threat. We employ a classic sensory-motor integrative schema to describe the peripheral, hindbrain, and hypothalamic components that make up counterregulatory mechanisms in the brain. We propose that models previously developed to describe how the forebrain modulates autonomic reflex loops in the hindbrain offer a reasoned framework for explaining how counterregulatory neural mechanisms in the hypothalamus and hindbrain are structured.

Heme oxygenase/carbon monoxide-biliverdin pathway down regulates neutrophil rolling, adhesion and migration in acute inflammation

BACKGROUND AND PURPOSE

Heme oxygenase (HO) activity is known to down-regulate inflammatory events. Here, we address the role of HO and its metabolites, carbon monoxide (CO) and biliverdin (BVD), in leukocyte rolling, adhesion and neutrophil migration during inflammatory processes.

EXPERIMENTAL APPROACH

Intravital microscopy was used to evaluate leukocyte rolling and adhesion in the mesenteric microcirculation of mice. TNFalpha and IL-1beta were determined by ELISA and HO-1 protein expression by Western blot.

KEY RESULTS

Intraperitoneal challenge with carrageenan enhanced HO-1 protein expression in mesentery and bilirubin concentration in peritoneal exudates. Pretreatment of mice with a non-specific inhibitor of HO (ZnDPBG) or with a HO-1 specific inhibitor (ZnPP IX) enhanced neutrophil migration, rolling and adhesion on endothelium induced by carrageenan. In contrast, HO substrate (hemin), CO donor (DMDC) or BVD reduced these parameters. The reduction of neutrophil recruitment promoted by HO metabolites was independent of the production of chemotactic cytokines. Inhibitory effects of CO, but not of BVD, were counteracted by treatment with a soluble guanylate cyclase (sGC) inhibitor, ODQ. Furthermore, inhibition of HO prevented the inhibitory effect of a nitric oxide (NO) donor (SNAP) upon neutrophil migration, while the blockade of NO synthase (NOS) activity by aminoguanidine did not affect the CO or BVD effects.

CONCLUSIONS AND IMPLICATIONS

Metabolites of HO decreased leukocyte rolling, adhesion and neutrophil migration to the inflammatory site by a mechanism partially dependent on sGC. Moreover, inhibition by NO of neutrophil migration was dependent on HO activity.

Gray-scale ultrasonic properties of the normal and inflamed pancreas

Eighty-seven examinations of the pancreas in 52 patients with acute or chronic pancreatitis and 31 examinations in 31 normal subjects were reviewed. Demonstration of the portal and splenic veins served as a guidepost to the pancreas. The normal pancreas was indistinguishable from the surrounding tissues in a substantial minority of examinations, and the ultrasonic characteristics of the normal pancreas were quite variable. Acute pancreatitis was found to be characterized by swelling, loss of internal echoes, and loss of distinction between the pancreas and splenic vein. In 50% of patients with chronic inactive pancreatitis, the pancreas could not be identified. Ultrasound should precede endoscopic retrograde cholangiopancreatography whenever a pseudocyst might be present.

Diagnosis and management of intestinal ischaemic disorders

Although intestinal ischaemia is an infrequent event, early recognition and appropriate treatment can reduce the potential for a devastating outcome

Prospective study of the incidence and risk factors of postsplenectomy thrombosis of the portal, mesenteric, and splenic veins

HYPOTHESIS

Splenectomy is recognized as a cause of portal, mesenteric, and splenic vein thrombosis. The exact incidence of the complication and its predisposing factors are not known.

DESIGN

Prospective observational cohort study. The median follow-up time of the patients was 22.6 months.

SETTING

University surgical clinic in a teaching hospital.

PATIENTS

A total of 147 consecutive patients who underwent splenectomy in a 4-year period were enrolled in the study.

INTERVENTIONS

Preoperative and postoperative evaluation included ultrasonography with color Doppler flow imaging of the portal system, results of blood coagulation tests, fibrinogen levels, D-dimer levels, and complete blood counts. Operative sheets were recorded and reviewed. When portal system thrombosis (PST) was diagnosed, a complete control for acquired and congenital thrombophilia disorders was obtained.

MAIN OUTCOME MEASURES

Primary end points of the study were the assessment of the incidence of postsplenectomy PST and the identification of risk factors for its occurrence.

RESULTS

Portal system thrombosis occurred in 7 (4.79%) of 146 patients who underwent splenectomy. The age, sex, type or length of the operation, and use of preoperative and postoperative thromboprophylaxis with low molecular weight heparin did not prove to be significant factors in the occurrence of PST. Platelet count of more than 650 x 10(3)/microL and greater spleen weight (>650 g) was associated with the development of PST (P = .01, P = .03). Normal D-dimer levels on diagnosis of the complication showed a negative predictive value of 98%. Two of the affected patients were diagnosed with thrombophilia disorders. In a median follow-up period of 22.6 months, no other case of PST was recorded.

CONCLUSIONS

Postsplenectomy PST occurs in approximately 5% of patients. Possible risk factors are thrombocytosis, splenomegaly, and congenital thrombophilia disorders.

Splenic and portal venous obstruction in chronic pancreatitis. A prospective longitudinal study of a medical-surgical series of 266 patients

The aim of this study was a prospective search for splenoportal venous obstruction (SPVO) in a medical-surgical series of 266 patients with chronic pancreatitis who were followed up a mean time of 8.2 years. SPVO was systematically searched for using ultrasonography and then confirmed by angiography or computed tomography. SPVO was found in 35 patients (13.2%) but was symptomatic in only two. Initial obstruction involved the splenic vein in 22 patients, the portal vein in 10, and the superior mesenteric vein in three. Since venous obstruction extended from the splenic to the portal vein in five patients, the prevalence of portal obstruction was 5.6% (15/266). Acute pancreatitis and pseudocysts were the probable cause of SPVO in 91.4% of our cases. Half the cases of splenic venous obstruction were related to pseudocysts of the caudal pancreas. Esophageal varices were found in two patients and gastric varices in four at the time of diagnosis and during follow-up. At the end of follow-up, 12 patients had undergone splenopancreatectomy (N = 11) or splenectomy (N = 1). Only one patient was operated on for massive esophageal variceal bleeding, and another patient died due to intractable colic variceal bleeding. In four of six patients operated on with portal vein obstruction, surgery was difficult due to venous collaterals. Ten patients were not operated on and 13 patients operated on were not treated for SPVO. The mean follow-up after diagnosis of SPVO for these final 23 patients was 28.9 months. None of these patients bled.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure to improve outcome in acute mesenteric ischaemia: seven-year review

OBJECTIVE

To determine whether the prognosis of acute mesenteric ischaemia has changed over the past seven years.

DESIGN

Retrospective study.

SETTING

Teaching hospital, Scotland.

SUBJECTS

57 patients who presented to this hospital between January 1987 and December 1993 with acute mesenteric ischaemia.

MAIN OUTCOME MEASURES

Morbidity, mortality and prognostic features.

RESULTS

46 of the 57 patients died. Only 18(32%) patients were accurately diagnosed before operation or death. Clinical presentation, white cell count, and serum amylase activity were not helpful in the diagnosis. Only 3 patients had mesenteric angiography, and none were given lytic agents or vasodilators.

CONCLUSION

Mortality from acute mesenteric ischaemia has not changed during the past two decades and in the absence of an accurate diagnostic test is unlikely to do so.

Review article: diagnosis and management of mesenteric ischaemia with an emphasis on pharmacotherapy

Mesenteric ischaemia results from decreased blood flow to the bowel, causing cellular injury from lack of oxygen and nutrients. Acute mesenteric ischaemia (AMI) is an uncommon disorder with high morbidity and mortality, but outcomes are improved with prompt recognition and aggressive treatment. Five subgroups of AMI have been identified, with superior mesenteric artery embolism (SMAE) the most common. Older age and cardiovascular disease are common risk factors for AMI, excepting acute mesenteric venous thrombosis (AMVT), which affects younger patients with hypercoaguable states. AMI is characterized by sudden onset of abdominal pain; a benign abdominal exam may be observed prior to bowel infarction. Conventional angiography and more recently, computed tomography angiography, are the cornerstones of diagnosis. Correction of predisposing conditions, volume resuscitation and antibiotic treatment are standard treatments for AMI, and surgery is mandated in the setting of peritoneal signs. Intra-arterial vasodilators are used routinely in the treatment of non-occlusive mesenteric ischaemia (NOMI) and also are advocated in the treatment of occlusive AMI to decrease associated vasospasm. Thrombolytics have been used on a limited basis to treat occlusive AMI. A variety of agents have been studied in animal models to treat reperfusion injury, which sometimes can be more harmful than ischaemic injury. Chronic mesenteric ischaemia (CMI) usually is caused by severe obstructive atherosclerotic disease of two or more splanchnic vessels, presents with post-prandial pain and weight loss, and is treated by either surgical revascularization or percutaneous angioplasty and stenting.

Mesenteric venous thrombosis

The prevalence of mesenteric venous thrombosis has increased over the past 2 decades with the routine use of contrast-enhanced computed tomography (CT) in patients presenting with abdominal pain and those with portal hypertension. Concurrent with increasing recognition, routine and frequent use of anticoagulation has reduced the need for surgical intervention and improved outcome in these patients. Acute thrombosis often presents with abdominal pain, whereas chronic disease manifests either as an incidental finding on CT or with features of portal hypertension. Contrast-enhanced CT diagnoses about 90% of cases. The presence of collateral circulation and cavernoma around a chronically thrombosed vein differentiates chronic from acute disease. The superior mesenteric vein is often involved, whereas involvement of the inferior mesenteric vein is rare. Associated portal venous thrombosis can be seen if the disease originates in the major veins instead of the small vena rectae. Thrombophilia and local abdominal inflammatory conditions are common causes. Management is aimed at preventing bowel infarction and recurrent thrombosis. Anticoagulation, the mainstay of management, has also been safely used in patients with cirrhosis and portal hypertension. This review discusses the pathogenesis of thrombosis of mesenteric veins, the diagnosis and differentiation from arterial ischemia, the emergence of the JAK2 (Janus kinase 2) sequence variation as a marker of thrombophilia and myelodysplastic neoplasms, and new anticoagulants. Algorithms for the management of acute and chronic mesenteric venous thrombosis are provided to help readers understand and remember the approach to the management of acute and chronic mesenteric venous thrombosis.

Mesenteric venous thrombosis

Mesenteric venous occlusion produces a spectrum of clinical presentations, the most common of which is the acute onset of abdominal pain with progressive signs and symptoms of bowel infarction. This acute form of mesenteric venous thrombosis, compared with other forms of acute mesenteric infarction, occurs in younger patients, typically has a more indolent and nonspecific course, involves shorter segments of bowel, and has a lower mortality rate. In contradistinction to our recommended therapy in other forms of acute mesenteric infarction, immediate anticoagulation is indicated for mesenteric venous thrombosis. Second-look operations are used, as in other forms of acute mesenteric infarction, whenever portions of bowel of questionable viability are not resected at the primary operation. Chronic mesenteric venous thrombosis may produce no symptoms or may cause gastrointestinal bleeding from portal hypertension. Newer imaging techniques have increased the ability to diagnose and define the extent of all forms of mesenteric venous thrombosis and have added to the therapeutic options available to manage them.

Mesenteric venous thrombosis: diagnosis and noninvasive imaging

Mesenteric venous thrombosis is an uncommon but potentially lethal cause of bowel ischemia. Several imaging methods are available for diagnosis, each of which has advantages and disadvantages. Doppler ultrasonography allows direct evaluation of the mesenteric and portal veins, provides semiquantitative flow information, and allows Doppler waveform analysis of the visceral vessels; however, it is operator dependent and is often limited by overlying bowel gas. Conventional contrast material-enhanced computed tomography (CT) allows sensitive detection of venous thrombosis within the central large vessels of the portomesenteric circulation and any associated secondary findings; however, it is limited by respiratory misregistration, motion artifact, and substantially decreased longitudinal spatial resolution. Helical CT and CT angiography, especially when performed with multi-detector row scanners, and magnetic resonance (MR) imaging, particularly gadolinium-enhanced MR angiography, enable volumetric acquisitions in a single breath hold, eliminating motion artifact and suppressing respiratory misregistration. Helical CT angiography and three-dimensional gadolinium-enhanced MR angiography should be considered the primary diagnostic modalities for patients with a high clinical suspicion of mesenteric ischemia. Conventional angiography is reserved for equivocal cases at noninvasive imaging and is also used in conjunction with transcatheter therapeutic techniques in management of symptomatic portal and mesenteric venous thrombosis.

Cross-bridge kinetics, cooperativity, and negatively strained cross-bridges in vertebrate smooth muscle. A laser-flash photolysis study

The effects of laser-flash photolytic release of ATP from caged ATP [P3-1(2-nitrophenyl)ethyladenosine-5'-triphosphate] on stiffness and tension transients were studied in permeabilized guinea pig protal vein smooth muscle. During rigor, induced by removing ATP from the relaxed or contracting muscles, stiffness was greater than in relaxed muscle, and electron microscopy showed cross-bridges attached to actin filaments at an approximately 45 degree angle. In the absence of Ca2+, liberation of ATP (0.1-1 mM) into muscles in rigor caused relaxation, with kinetics indicating cooperative reattachment of some cross-bridges. Inorganic phosphate (Pi; 20 mM) accelerated relaxation. A rapid phase of force development, accompanied by a decline in stiffness and unaffected by 20 mM Pi, was observed upon liberation of ATP in muscles that were released by 0.5-1.0% just before the laser pulse. This force increment observed upon detachment suggests that the cross-bridges can bear a negative tension. The second-order rate constant for detachment of rigor cross-bridges by ATP, in the absence of Ca2+, was estimated to be 0.1-2.5 X 10(5) M-1s-1, which indicates that this reaction is too fast to limit the rate of ATP hydrolysis during physiological contractions. In the presence of Ca2+, force development occurred at a rate (0.4 s-1) similar to that of intact, electrically stimulated tissue. The rate of force development was an order of magnitude faster in muscles that had been thiophosphorylated with ATP gamma S before the photochemical liberation of ATP, which indicates that under physiological conditions, in non-thiophosphorylated muscles, light-chain phosphorylation, rather than intrinsic properties of the actomyosin cross-bridges, limits the rate of force development. The release of micromolar ATP or CTP from caged ATP or caged CTP caused force development of up to 40% of maximal active tension in the absence of Ca2+, consistent with cooperative attachment of cross-bridges. Cooperative reattachment of dephosphorylated cross-bridges may contribute to force maintenance at low energy cost and low cross-bridge cycling rates in smooth muscle.