Effects of acute normovolemic anemia on gastric mucosal blood flow in rats: role of nitric oxide

A matched case-control study of a novel Acid-pump antagonist and proton-pump inhibitor for the treatment of iatrogenic ulcers caused by endoscopic submucosal dissection

BACKGROUND/AIMS

Revaprazan, a novel acid-pump antagonist, and proton-pump inhibitors (PPIs) have pH-independent effects on ulcer healing. The addition of a PPI promotes the cell restitution rate as well as vessel regeneration and maturation for ulcer repair. Revaprazan is known to protect the mucosa by increasing the prostaglandin concentration.

METHODS

We reviewed the medical records of patients who underwent endoscopic submucosal dissection (ESD) for gastric neoplasia at Yeungnam University Hospital between January 2008 and May 2009. We conducted a matched case-control study to compare the healing rates effected by revaprazan and rabeprazole.

RESULTS

Each group consisted of 30 patients. The baseline characteristics did not differ significantly between the two groups. Stage S1 disease was observed in 97% and 100% of patients after 8 weeks of treatment in the revaprazan and rabeprazole groups, respectively. In the revaprazan group, only one patient had stage H2 disease: a 54-year-old man with a 5.5-cm lesion after ESD of the ulcer, type IIa early gastric cancer, and adenocarcinoma. No serious adverse effects occurred during the treatment period in either group.

CONCLUSIONS

The safety and efficacy profiles of revaprazan and rabeprazole are similar for the treatment of ESD-induced ulcers.

Degree of healing and healing-associated factors of endoscopic submucosal dissection-induced ulcers after pantoprazole therapy for 4 weeks

BACKGROUND

There is no consensus regarding the degree of healing of endoscopic submucosal dissection (ESD)-induced ulcers and the optimal duration of proton pump inhibitor (PPI) treatment.

AIM

To evaluate the degree of healing and the factors associated with healing of ESD-induced ulcers after PPI therapy for 4 weeks.

METHODS

Fifty-six patients who underwent complete ESD for adenoma or early gastric cancer were enrolled. All patients underwent follow-up endoscopy to evaluate the degree of ulcer healing after pantoprazole therapy (40 mg per day) for 4 weeks. We evaluated change in size of ESD-induced ulcers between baseline and 4 weeks, and correlated relevant factors with degree of healing of small and large ulcers.

RESULTS

At follow-up, 28 (50%) patients had large ulcers (area > 10 mm(2)). Ulcer size at 4 weeks was closely correlated with initial ulcer size (P < 0.001) and abruptly increased when initial ulcer size was larger than 4 cm. Comorbidity, procedure time, and initial specimen size were significantly associated with healing rate, but multivariate analysis showed that initial ulcer size was the only significant parameter (P < 0.015).

CONCLUSIONS

Healing degree of ESD-induced ulcers at 4 weeks is dependent on initial ulcer size, indicating that duration of treatment with PPI should be dependent on initial ulcer size.

Heart, kidney, and intestine have different tolerances for anemia

Organ systems do not respond uniformly to changes in systemic oxygen delivery because of global and local redistributive mechanisms. We hypothesized that progressive hemodilution would evoke a different response in the microvascular oxygenation of the heart compared with kidney and gut. To evaluate this hypothesis, we studied the effect of stepwise isovolemic hemodilution on systemic hemodynamic and oxygenation parameters as well as the relation between systemic hematocrit (Ht) and microvascular PO(2) (microPO(2)) in heart, kidney, and intestines in an anesthetized and mechanically ventilated rat model. Baseline conditions were similar in the hemodilution group and in the control group. In the hemodilution group, Ht was diminished from 46.6 +/- 3.8% to 7.0 +/- 1.8% [mean +/- standard deviation (SD)]. This group had no effect on measured hemodynamics; only when Ht fell below 10% did blood pressure start to decrease. The microPO(2) values in heart, kidney, and intestines did not respond uniformly. Renal microPO(2) (56 +/- 10 mm Hg at baseline) started to decrease at a Ht of 38.5 +/- 8.6%, whereas intestinal microPO(2) (59 +/- 6 mm Hg at baseline) did not start to decrease until Ht reached 17.4 +/- 7.1%. Finally, cardiac microPO(2) (40 +/- 6 mm Hg at baseline) decreased only in the ultimate stage of the experiment at Ht of 8.7 +/- 3.5%. Based on these observations, we conclude that the regulation of microvascular oxygenation during progressive anemia is specific for each organ system. The relation between these observations and organ function and damage needs to be determined.

Animal models of portal hypertension

Animal models have allowed detailed study of hemodynamic alterations typical of portal hypertension and the molecular mechanisms involved in abnormalities in splanchnic and systemic circulation associated with this syndrome. Models of prehepatic portal hypertension can be used to study alterations in the splanchnic circulation and the pathophysiology of the hyperdynamic circulation. Models of cirrhosis allow study of the alterations in intrahepatic microcirculation that lead to increased resistance to portal flow. This review summarizes the currently available literature on animal models of portal hypertension and analyzes their relative utility. The criteria for choosing a particular model, depending on the specific objectives of the study, are also discussed.

Intravenous nitroglycerin does not preserve gastric microcirculation during gastric tube reconstruction: a randomized controlled trial

Introduction

Complications of oesophagectomy and gastric tube reconstruction include leakage and stenosis, which may be due to compromised microvascular blood flow (MBF) in gastric tissue. We recently demonstrated that decreased MBF could be improved perioperatively by topical administration of nitroglycerin. The aim of the present study was to investigate whether nitroglycerin, administered intravenously during gastric tube reconstruction, could preserve tissue blood flow and oxygenation in the gastric fundus, and reduce the incidence of postoperative leakage.

Methods

In this single-centre, prospective, double-blinded study, we randomized 32 patients scheduled for oesophagectomy into two groups. The intervention group received intravenous nitroglycerin during gastric tube reconstruction, and the control group received normal saline. Baseline values for MBF, microvascular haemoglobin oxygen saturation and microvascular haemoglobin concentration were determined at the gastric fundus before and after gastric tube construction and after pulling up the gastric tube to the neck.

Results

MBF and microvascular haemoglobin oxygen saturation decreased similarly in both groups during gastric tube reconstruction and were comparable. The oesophageal anastomosis was controlled by contrast radiography before discharge from the hospital; leakage was observed in two patients (13%) in the nitroglycerin group and five patients (31 %) in the control group (not significant).

Conclusion

Under stable systemic haemodynamic conditions, continuous intravenous administration of nitroglycerin could not prevent deterioration in gastric microvascular perfusion and microvascular haemoglobin saturation during gastric tube reconstruction. (Trial registration number NCT 00335010.)

Animal models of portal hypertension

Animal models have allowed detailed study of hemodynamic alterations typical of portal hypertension and the molecular mechanisms involved in abnormalities in splanchnic and systemic circulation associated with this syndrome. Models of prehepatic portal hypertension can be used to study alterations in the splanchnic circulation and the pathophysiology of the hyperdynamic circulation. Models of cirrhosis allow study of the alterations in intrahepatic microcirculation that lead to increased resistance to portal flow. This review summarizes the currently available literature on animal models of portal hypertension and analyzes their relative utility. The criteria for choosing a particular model, depending on the specific objectives of the study, are also discussed.

Modelos animales en el estudio de la hipertensión portal

Animal models allow detailed study of the hemodynamic alterations in portal hypertension syndrome and of the molecular mechanisms involved in the abnormalities in splenic and systemic circulation associated with this syndrome. Models of prehepatic portal hypertension can be used to study alterations in the splenic circulation and the physiopathology of hyperdynamic circulation. Moreover, models of cirrhosis allow the alterations in intrahepatic microcirculation that lead to increased resistance to portal flow to be studied. The present review summarizes currently available animal models of portal hypertension and analyzes their relative utility in investigating the distinct disorders associated with this entity. The criteria for the choice of a particular model, depending on the specific objectives of the study, are also discussed.

Redistribution of intestinal microcirculatory oxygenation during acute hemodilution in pigs

Acute normovolemic hemodilution (ANH) compromizes intestinal microcirculatory oxygenation; however, the underlying mechanisms are incompletely understood. We hypothesized that contributors herein include redistribution of oxygen away from the intestines and shunting of oxygen within the intestines. The latter may be due to the impaired ability of erythrocytes to off-load oxygen within the microcirculation, thus yielding low tissue/plasma Po2 but elevated microcirculatory hemoglobin oxygen (HbO2) saturations. Alternatively, oxygen shunting may also be due to reduced erythrocyte deformability, hindering the ability of erythrocytes to enter capillaries. Anesthetized pigs underwent ANH (20, 40, 60, and 90 ml/kg hydroxyethyl starch; ANH group: n = 10; controls: n = 5). We measured systemic and mesenteric perfusion. Microvascular intestinal oxygenation was measured independently by remission spectrophotometry [microcirculatory HbO2 saturation (μHbO2)] and palladium-porphyrin phosphorescence quenching [microcirculatory oxygen pressure in plasma/tissue (μPo2)]. Microcirculatory oxygen shunting was assessed as the disparity between mucosal and mesenteric venous HbO2 saturation (HbO2-gap). Erythrocyte deformability was measured as shear stress-induced cell elongation (LORCA difractometer). ANH reduced hemoglobin concentration from 8.1 to 2.2 g/dl. Relative mesenteric perfusion decreased (decreased mesenteric/systemic perfusion fraction). A paralleled reduction occurred in mucosal μHbO2 (68 ± 2 to 41 ± 3%) and μPo2 (28 ± 1 to 17 ± 1 Torr). Thus the proposed constellation indicative for oxygen off-load deficits (sustained μHbO2 at decreased μPo2) did not develop. A twofold increase in the HbO2-gap indicated increasing intestinal microcirculatory oxygen shunting. Significant impairment in erythrocyte deformability developed during ANH. We conclude that reduced intestinal oxygenation during ANH is, in addition to redistribution of oxygen delivery away from the intestines, associated with oxygen shunting within the intestines. This shunting appears to be not primarily caused by oxygen off-load deficit but rather by oxygen/erythrocytes bypassing capillaries, wherein a potential contributor is impaired erythrocyte deformability.

Review article: the relevance of portal pressure and other risk factors in acute gastro-oesophageal variceal bleeding

Gastro-oesophageal variceal bleeding is the last step in a chain of events that starts with an increased portal pressure, and is followed by the formation and progressive dilatation of gastro-oesophageal varices. When the tension of the thin wall of the varices exceeds its elastic limit, the varices rupture and bleed. Wall tension is directly proportional to variceal pressure (which is a function of portal pressure) and variceal radius, and inversely related to the thickness of the variceal wall. The above facts explain why a high portal pressure (usually determined by the hepatic venous pressure gradient, or HVPG) and the presence at endoscopy of large varices with red wheals, red spots or diffuse redness on the varices (signalling a reduced wall thickness) correlate with the risk of bleeding.

Healing rate of EMR-induced ulcer in relation to the duration of treatment with omeprazole

BACKGROUND

Although EMR-induced ulcers heal faster and recur less often than noniatrogenic gastric ulcers, there is no consensus regarding the duration of therapy for these ulcers. This study prospectively evaluated healing of EMR-induced ulcers according to the duration of omeprazole therapy.

METHODS

A total of 69 patients were randomly assigned, after EMR, to treatment with omeprazole (20 mg per day) for 7 days (1-week group) or with omeprazole (20 mg per day) for 28 days (4-week group). Four weeks after EMR, ulcer size and stage were compared with those of the initial EMR-induced ulcer. Each patient kept a daily diary of drugs consumed and ulcer-related symptoms during the 4-week period after EMR.

RESULTS

Thirty-four patients were randomized to the 4-week group, and 26 were randomized to the 1-week group. No significant differences were observed between the two groups at 4 weeks after EMR in terms of ulcer reduction ratio (p=0.29) or stage (p=0.11). In addition, no difference was observed between the two groups with respect to ulcer-related symptoms or use of additional gastric-coating medication (p=0.48).

CONCLUSIONS

For EMR-induced ulcer, treatment with omeprazole for 1 week is equivalent to treatment for 4 weeks. Short-term therapy with omeprazole can be considered for EMR-induced ulcer.

Serum and ascitic fluid nitrate levels in patients with cirrhosis

BACKGROUND

Increased nitric oxide level may play a critical role in the hemodynamic disturbances in patients with cirrhosis. There are few reports investigating the factors related to this increase and their results are controversial. The purpose of this study was to reveal the clinical importance of nitric oxide levels and the possible factors related to this increase in patients with cirrhosis.

METHODS

Serum and ascites nitrate levels were studied in 50 patients with cirrhosis and 10 control subjects.

RESULTS

All cirrhotic patients (groups 2, 3, 4, 5, 6) showed significant increase in serum nitrate levels in comparison with that in control subjects (group 1) (p<0.001). Serum nitrate levels were significantly higher (282.4+/-111.3 micromol/l; p<0.05) in patients with spontaneous bacterial peritonitis (group 2) when compared with those in cirrhotic patients without spontaneous bacterial peritonitis (group 3) (186.4+/-87.6 micromol/l). Ascitic fluid nitrate levels were significantly higher (302.4+/-66 micromol/l; p<0.001) in patients with spontaneous bacterial peritonitis (group 2) when compared with those in cirrhotic patients without spontaneous bacterial peritonitis (group 3) (135.4+/-65.8 micromol/l). Serum nitrate levels were significantly lower in cirrhotic patients without ascites (group 5) when compared with those in cirrhotic patients with ascites (group 3) (98.8+/-52.6 vs. 186.4+/-87.6 micromol/l; p<0.05). No significant differences were found among patients with severe anemia (groups 4, 6) and other cirrhotic patients (group 3) (174.5+/-54.5, 168.8+/-63.8 vs. 186.4+/-87.6 micromol/l; p>0.05). Cirrhotic patients with Child--Pugh B and C scores showed higher serum nitrate levels (179.4+/-81.1, 222.5+/-101.7 micromol/l; p<0.001) than did cirrhotic patients with Child--Pugh A score (85.8+/-59.7 micromol/l).

CONCLUSION

Our findings suggest that overproduction of nitric oxide in cirrhotic patients may be related to the severity of liver damage and spontaneous bacterial peritonitis but not related to their anemia.

Preservation of intestinal microvascular Po2 during normovolemic hemodilution in a rat model

The effect of hemodilution on the intestinal microcirculatory oxygenation is not clear. The aim of this study was to determine the effect of moderate normovolemic hemodilution on intestinal microvascular partial oxygen pressure (Po2) and its relation to the mesenteric venous Po2 (Pmvo2). Normovolemic hemodilution was performed in 13 anesthetized male Wistar rats. Systemic hemodynamic and intestinal oxygenation parameters were monitored. Intestinal microvascular Po2 was measured by using the oxygen-dependent quenching of palladium-porphyrin phosphorescence. Hemodilution decreased systemic hematocrit from 45.0% +/- 0.1% (average +/- SEM) to 24.6% +/- 1.6%. The mesenteric blood flow did not change from baseline values, resulting in a linear decrease in intestinal oxygen delivery (from 2.77 +/- 0.15 to 1.42 +/- 0.11 mLxkg(-1)xmin(-1)). The intestinal oxygen extraction ratio increased significantly from 24% +/- 1% to 42% +/- 4%. Pmvo2 decreased significantly (from 57 +/- 2 to 41 +/- 2 mm Hg), but intestinal oxygen consumption and microvascular Po2 remained unaffected. As a result, the difference between microvascular Po2 and Pmvo2 increased significantly during hemodilution. Intestinal microvascular Po2 and oxygen consumption were well preserved during moderate normovolemic hemodilution. These results might be explained by the notion of others that hemodilution induces recruitment of capillaries, resulting in redistribution of the intestinal blood flow in favor of the microcirculation, which allows a more efficient extraction of oxygen. These findings further indicate that the use of venous Po2 values as indicators of microvascular oxygenation may be misleading.

Nitric oxide does not play a major role in the regulation of systemic hemodynamic responses to acute normovolemic hemodilution

BACKGROUND

The mechanisms of cardiovascular changes following acute normovolemic hemodilution (ANH) have not been fully elucidated. We tested the hypothesis that inhibition of nitric oxide synthesis attenuates ANH-induced cardiovascular responses.

METHODS

We observed the effects of N(omega)-nitro-L-arginine methyl ester (L-NAME) pretreatment on ANH-induced cardiovascular responses and compared these effects with those elicited by phenylephrine (PHE). Twenty dogs anesthetized with isoflurane were divided into two groups: one group was pretreated with L-NAME and the other with PHE. Both groups were normovolemically hemodiluted using 6% hydroxyethyl starch to reduce the hemoglobin concentration to approximately 50% of the pretreatment value.

RESULTS

Pretreatment with either L-NAME or PHE caused a significant increase in mean aortic blood pressure (MAP) and systemic vascular resistance (SVR) with a significant decrease in cardiac output (CO) and stroke volume (SV). However, no remarkable differences in these variables were seen between groups. In both groups ANH produced increases in heart rate, CO, SV, and maximal left ventricular dP/dt with a significant decrease in SVR. No significant differences in these variables were apparent after ANH except that MAP was decreased in the PHE group but not in the L-NAME group.

CONCLUSION

Our results suggest that nitric oxide does not play a major role in mediation or modulation of the systemic vascular responses to ANH.

Type I nitric oxide synthase (NOS) is the predominant NOS in rat small intestine. Regulation by platelet-activating factor

Constitutive nitric oxide synthase (cNOS) may play an important protective role in the intestine, since our previous study has shown that the degree of bowel injury induced by platelet-activating factor (PAF), a potent inflammatory mediator, is inversely related to the cNOS content of the intestine. This study aims to examine the composition of the cNOS system in rat small intestine, and its regulation by PAF. We found that an approximately 120 kDa NOS I (neuronal NOS) is the predominant NOS in rat intestine, as evidenced by the following: (a) immunoblotting with specific antibodies detected a NOS I of approximately 120 kDa, but little NOS III; (b) the Ca(2+)-dependent, constitutive NOS (cNOS) activity of the rat intestine was removed by immunoprecipitation with the anti-NOS I, but not anti-NOS II or anti-NOS III antibodies; (c) RT-PCR revealed constitutive expression of NOS I in the intestinal tissue, but only a minute amount of NOS III. Immunofluorescent staining with anti-NOS I located NOS in the Auerbach plexus and nerve fibers in the muscle layer. We also found that this 120 kDa NOS I is rapidly (within 1 h) down-regulated in response to PAF administration. The protein level, enzyme activity as well as mRNA of nNOS were all decreased in the intestine.

Effects of increasing blood hemoglobin levels on systemic hemodynamics of acutely anemic cirrhotic patients

BACKGROUND/AIMS

In experimental portal hypertension, blood hemoglobin levels have been shown to influence the hyperdynamic circulatory state. The aim of this study was to assess the hemodynamic effects of increasing hemoglobin concentration in human portal hypertension.

METHODS

Sixteen cirrhotic patients recovering from a variceal bleeding episode were randomly assigned to receive two units of packed red cells or 500 ml of a protein solution. Systemic and portal hemodynamics, and rheological and hormonal parameters were measured at baseline and after expansion.

RESULTS

Both groups were similar with respect to the degree of liver failure, severity of the bleeding episode, activation of the endogenous vasopressor systems, and hemodynamic parameters. The administration of either erythrocytes or a protein solution prompted a similar increase in total blood volume and suppression of vasopressor systems. Both groups of patients experienced similar increases in wedged hepatic venous pressure. Hepatic venous pressure gradient was not significantly modified but tended to increase in erythrocyte-transfused patients. Cardiopulmonary pressures increased, but this increment was significant in the non-blood-transfused patients only. Cardiac output decreased in erythrocyte-transfused patients, while it increased in the group receiving a protein solution. Red blood cell transfusion resulted in an increase in systemic vascular hindrance (resistance/blood viscosity), whereas the administration of a protein solution prompted a decrease in this parameter, thus reflecting true vasoconstriction and vasodilation, respectively.

CONCLUSIONS

An increase in blood hemoglobin in acutely anemic cirrhotic patients attenuates their hyperdynamic circulation beyond viscosity-dependent changes, an effect which might be counteracted by the effects on portal venous pressure gradient.

Gastric intramucosal acidosis in mechanically ventilated patients: role of mucosal blood flow

OBJECTIVE

To investigate whether gastric intramucosal acidosis is associated with a decreased gastric mucosal blood flow in mechanically ventilated patients.

DESIGN

Prospective, clinical investigation.

SETTING

University hospital intensive care unit.

PATIENTS

Seventeen mechanically ventilated patients with stable hemodynamic status.

INTERVENTIONS

Gastric tonometry and endoscopic assessment of mucosal blood flow.

MEASUREMENTS AND MAIN RESULTS

Six patients had gastric intramucosal acidosis (intramucosal pH [pHi] of 7.24 +/- 0.06), whereas the remaining 11 patients had pHi values within the normal range (7.44 +/- 0.01). No differences were found between intramucosal acidotic and nonacidotic patients with respect to their general and hemodynamic characteristics. Patients with intramucosal acidosis had a lower gastric mucosal blood flow, as assessed by laser-Doppler flowmetry, than nonacidotic patients (1.4 +/- 0.1 vs. 2.1 +/- 0.2 volts, respectively; p < .05). Reflectance spectrophotometry disclosed that patients with low gastric pHi had also a significantly (p < .05) lower hemoglobin content index (61 +/- 4 arbitrary units) than patients with normal pHi (81 +/- 3 arbitrary units), whereas oxygen saturation index was similar for both groups.

CONCLUSION

Our results support the hypothesis that gastric mucosal hypoperfusion underlies the development of intramucosal acidosis in mechanically ventilated patients.

Downregulation of nitric oxide synthase in chronic renal insufficiency: role of excess PTH

The available data on the effect of chronic renal failure (CRF) on nitric oxide (NO) metabolism are limited and contradictory. We studied rats with CRF 6 wk after a five-sixths nephrectomy and compared the results with those in the sham-operated controls, felodipine-treated CRF, and parathyroidectomized (CRF-PTX) animals. CRF was produced by surgical resection of the upper and lower thirds of the left kidney, followed by contralateral nephrectomy. We chose this model, as opposed to that produced by renal artery branch ligation, because the latter causes exuberant hypertension (HTN), which independently affects NO metabolism. The CRF group exhibited a mild HTN coupled with elevated basal platelet cytosolic Ca2+ concentration ([Ca2+]i), blunted hypotensive response to L-arginine, decreased hypertensive response to NO synthase (NOS) inhibitor, NG-monomethyl-L-arginine, and normal hypotensive response to NO donor, sodium nitroprusside. This was associated with a significant reduction in urinary excretion of stable NO metabolites (NOX) and depressed NOS activity, as well as endothelial and inducible NO synthase (eNOS and iNOS, respectively) protein contents of thoracic aorta and the remnant kidney in the CRF animals. Calcium channel blockade and PTX lowered blood pressure, increased urinary NOX, and enhanced vascular NOS activity, as well as eNOS and iNOS protein expressions in the tested tissues. Thus CRF animals exhibited significant reductions in vascular NOS activity and eNOS and iNOS expressions. These abnormalities were reversed by calcium channel blockade and PTX, suggesting the possible causal role of CRF-induced dysregulation of [Ca2+]i.

Up-regulation of renal and vascular nitric oxide synthase in iron-deficiency anemia

Anemia is frequently associated with increased cardiac output and reduced vascular resistance. The latter has been attributed to reduced inactivation of nitric oxide (NO) by hemoglobin. We hypothesized that in addition to reducing NO inactivation, anemia may up-regulate NO production. To test this hypothesis, male Sprague-Dawley rats with chronic iron-deficiency anemia (produced by multiple phlebotomies and an iron-free diet) were studied. The results were compared with those obtained in a group of normal control animals. The anemic group showed marked increases in urinary excretion, plasma concentration, and renal and aorta tissue contents of NO metabolites (total nitrates and nitrites, NOx). This was accompanied by a significant rise in urinary excretion of cGMP, the second messenger for NO. In addition, NO synthase (NOS) activity and endothelial constitutive (ecNOS) and inducible NOS (iNOS) proteins of the thoracic aorta were markedly increased in the anemic group. Likewise, renal tissue ecNOS and iNOS proteins were greatly increased in the anemic animals. NOS activity and protein values were inversely related to hematocrit and directly related to plasma, tissue and urinary NOx. The constellation of these findings points to an increased NOS expression and NO production as opposed to the mere reduction of NO inactivation in iron-deficiency anemia. Further studies are planned to determine the mechanism of NOS up-regulation in iron-deficiency anemia.

Portal Hypertensive gastropathy

The term portal hypertensive gastropathy (PHG) defines a wide spectrum of diffuse macroscopic lesions that appear in the gastric mucosa of patients with portal hypertension. Histologically, these lesions correspond to dilated vessels in the mucosa and submucosa in the absence of erosions or inflammation. Endoscopically, the lesions are classified as mild when mosaic pattern or superficial reddening are present, and severe when gastric mucosa appear with diffuse cherry red spots. Mild lesions are highly prevalent (65-90%), whereas severe lesions are present in only 10-25% of cirrhotic patients. The pathogenesis of PHG is not well known, but both venous congestion related with raised portal pressure and increased gastric blood flow seem to be crucial factors for its development. Variceal sclerosis may contribute to the development or aggravation of the lesions. Bleeding is the unique clinical manifestation of PHG, and occurs only in those patients with severe lesions. During a 5-year follow-up, the risk of overt bleeding or chronic bleeding, which induces anaemia, is 60 % and 90%, respectively, for patients with severe PHG. Propranolol is the only pharmacological treatment that has been proven useful in preventing bleeding from PHG. Porto-systemic shunts and liver transplantation are also effective.

The effects of progressive anemia on jejunal mucosal and serosal tissue oxygenation in pigs

Anemia may promote intestinal hypoxia. We studied the effects of progressive isovolemic hemodilution on jejunal mucosal (Po2muc), and serosal tissue oxygen tension (Po2ser, Clark-type surface electrodes), mucosal microvascular hemoglobin oxygen saturation (Hbo2muc), and hematocrit (Hctmuc; tissue reflectance spectophotometry) in a jejunal segment. Twelve domestic pigs were anesthetized, paralyzed, and mechanically ventilated. Laparatomy was performed, arterial supply of a jejunal segment isolated, and constant pressure pump perfused. Seven animals were progressively hemodiluted to systemic hematocrits (Hctsys) of 20%, 15%, 10%, and 6%. Baseline for Po2muc, Po2ser and Hbo2muc was 23.5 +/- 2.1 mm Hg, 57.5 +/- 4 mm Hg, and 47.0% +/- 6.4% which were not different from the five controls. Despite a significant increase in jejunal blood flow, jejunal oxygen delivery decreased and oxygen extraction ratio increased significantly at Hctsys 10% and 6%. Po2ser decreased significantly below or at Hctsys of 15%, whereas Po2muc and Hbo2muc were maintained to Hctsys of 10%, but less than 10% Hbo2muc and mesenteric venous pH decreased significantly, implying that physiological limits of jejunal microvascular adaptation to severe anemia were reached. Decrease of Hctmuc was less pronounced than Hctsys. In conclusion, redistribution of jejunal blood flow and an increase in the ratio of mucosal to systemic hematocrit are the main mechanisms maintaining mucosal oxygen supply during progressive anemia.

Anemia increases gastric blood flow in noncirrhotic and cirrhotic patients

BACKGROUND

Previous studies in rats have demonstrated that anemia induces a significant increment in gastric mucosal blood flow. In the present study, we investigated whether chronic anemia induces similar changes in gastric blood perfusion in humans, and if this effect is also present in cirrhotic patients in whom gastric blood flow is usually increased in basal conditions.

METHODS

Gastric mucosal blood perfusion was assessed by means of laser-Doppler flowmetry and reflectance spectrophotometry applied through the endoscope.

RESULTS

Anemia significantly increases laser-Doppler signal in cirrhotic (2.3 +/- 0.11 vs 2.9 +/- 0.22 volts, p < 0.05) and noncirrhotic patients (1.71 +/- 0.15 vs 2.24 +/- 0.17, p < 0.05). In anemic patients the index of hemoglobin concentration of the gastric mucosa, assessed by reflectance spectrophotometry, was significantly decreased in cirrhotic patients (107.6 +/- 4.7 vs 95.5 +/- 3.3, p < 0.05) and noncirrhotic patients (93.9 +/- 4.1 vs 76.1 +/- 4.2, p < 0.01), whereas the index of oxygen saturation was increased (36.7 +/- 0.7 vs 40.4 +/- 1.4, p = 0.05; and 36.4 +/- 1.1 vs 43.2 +/- 1.9, p < 0.01, respectively).

CONCLUSIONS

In conclusion, chronic anemia is associated with an enhanced gastric blood perfusion reflected by an increased laser-doppler signal and gastric mucosal oxygen index despite a decrease in gastric hemoglobin concentration. In cirrhotic patients, anemia promotes a further increment in its basal gastric hyperemia.

Mechanism of systemic vasodilation during normovolemic hemodilution

In the nonfailing heart, normovolemic hemodilution increases cardiac output and decreases total peripheral resistance (TPR). Putative mechanisms mediating the decrease in TPR include reflex vasodilation and changes in the local regulation of blood flow. Our objectives were to determine whether ablation of reflex neural mechanisms or the inhibition of nitric oxide (NO) synthase, the enzyme responsible for the synthesis of the endothelium-derived relaxing factor (EDRF-NO), modulates the systemic vasodilator response to normovolemic hemodilution. Three groups of male Sprague-Dawley rats were subjected to acute normovolemic hemodilution, which was achieved by exchanging a volume of blood equivalent to 3.8% of body weight with hydroxyethyl starch. Hemodilution increased cardiac output and decreased TPR. Subsequent administration of the NO synthase inhibitor, L-nitroarginine (LNA), returned both cardiac output and TPR to control values. Pretreatment with LNA prior to hemodilution increased TPR, an effect that was partially reversed by the NO donor, sodium nitroprusside. In this setting, hemodilution failed to decrease TPR. After spinal cord destruction by "pithing," hemodilution decreased TPR to the same extent as that observed in intact rats. This hemodilution-induced decrease in TPR was abolished by the subsequent administration of LNA. These results indicate that neural reflexes do not modulate the systemic vascular response to hemodilution. Moreover, the systemic vasodilator response to hemodilution is abolished after inhibition of endogenous NO synthesis.

Evidence against a role for inducible nitric oxide synthase in the hyperdynamic circulation of portal-hypertensive rats

BACKGROUND/AIMS

Excessive nitric oxide biosynthesis caused by expression of inducible NO synthase has been implicated in the hyperdynamic circulation of portal hypertension. The aim of the study was to investigate whether inducible NO synthase is expressed in portal hypertension an accounts for the hyperdynamic circulation.

METHODS

In study 1, NO synthase activities were measured by the conversion of L-arginine to citrulline in tissues from portal-hypertensive, cirrhotic, and sham-operated rats and from normal rats pretreated with endotoxin and after long-term administration of dexamethasone, which inhibits the expression of inducible NO synthase. In study 2, systemic and splanchnic hemodynamics (radiolabeled microspheres) and gastric blood flow (hydrogen gas clearance and reflectance spectrophotometry) were measured in portal-hypertensive rats after long-term administration of dexamethasone (0.25 mg.kg-1.day-1) or vehicle.

RESULTS

In study 1, constitutive and inducible NO synthase activities in portal-hypertensive or cirrhotic rats were similar to those observed in sham-operated rats. The significant increase in the inducible activity observed after endotoxin injection was prevented when rats received long-term treatment with dexamethasone. In study 2, cardiac index, portal-pressure, portal venous inflow, and gastric blood flow were similar in dexamethasone-or vehicle-treated portal-hypertensive rats.

CONCLUSIONS

These results to not support a role for an increased expression of the inducible NO synthase in the hyperdynamic circulation of portal hypertension.

Acute normovolaemic anaemia prevents ethanol-induced gastric damage in rats through a blood flow related mechanism

The aim of the study was to assess whether changes in gastric mucosal blood flow induced by acute normovolaemic anaemia influence the susceptibility of the gastric mucosa to ethanol-induced damage, and the relationship of these changes with nitric oxide biosynthesis. Acute normovolaemic anaemia, promoted by exchanging 3 ml of blood by a plasma expander, induced a significant increase in gastric mucosal blood flow measured by hydrogen gas clearance, without changes in arterial blood pressure. After intragastric 60% ethanol administration, gastric blood flow was still significantly higher in anaemic than in control rats, and this was associated with a lower macroscopic and microscopic gastric damage. Following ethanol administration, anaemic rats pretreated with an inhibitor of nitric oxide biosynthesis (L-NMMA, 50 mg/kg, i.v.) had a lower gastric blood flow and a higher macroscopic gastric damage than anaemic rats without pretreatment. Anaemic rats pretreated with vasopressin also had after ethanol administration a lower gastric blood flow and a higher macroscopic gastric damage. It is concluded that acute normovolaemic anaemia protects the gastric mucosa against damage induced by intragastric ethanol. The inhibition of nitric oxide biosynthesis reverts in part this protective effect, and this seems to be related with the capability of nitric oxide to increase gastric mucosal blood flow, since vasoconstriction by a nitric oxide-independent mechanism causes a similar effect.

Effects of chronic normovolemic anemia on gastric microcirculation and ethanol-induced gastric damage in rats

The effects of chronic normovolemic anemia on gastric microcirculation and gastric mucosal susceptibility to ethanol-induced gastric damage were investigated in anesthetized rats. Blood exchange by a plasma expander during four consecutive days rendered the animals anemic with a 34% decrease in the baseline hematocrit but without affecting blood volume. Chronic anemia induced a decrease in whole blood viscosity, an increase in gastric mucosal blood flow measured by hydrogen gas clearance, a decrease in gastric vascular resistance, and a decrease in gastric hemoglobin content without changes in the gastric oxygen content, the latter two parameters being measured by reflectance spectrophotometry. Gastric mucosal blood flow was lowered by intragastric administration of 100% ethanol in both anemic and control rats, but the final blood flow was significantly higher in anemic than in control animals. Macroscopic gastric damage induced by ethanol administration was significantly lower in anemic than in control rats. We conclude that chronic normovolemic anemia increases gastric mucosal blood flow and leads a protecting mechanism against gastric mucosal damage induced by absolute ethanol.

Thirteenth Gaddum Memorial Lecture. Neuronal and endothelium-derived mediators in the modulation of the gastric microcirculation: integrity in the balance

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