Maria Casadevall

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.

Increased gastric mucosal perfusion in cirrhotic patients with portal hypertensive gastropathy

To characterize gastric mucosal perfusion in cirrhotic patients with portal hypertensive gastropathy, 34 cirrhotics with this lesion and 24 noncirrhotics were studied by reflectance spectrophotometry and laser-Doppler flowmetry during endoscopy. A significant correlation was observed between the hemoglobin content of the gastric mucosa, measured by reflectance spectrophotometry, and the serum hemoglobin concentration both in cirrhotics (r = 0.72) and in noncirrhotics (r = 0.87). IHb ratio (hemoglobin content of gastric mucosa divided by blood hemoglobin concentration) was higher in cirrhotics with portal hypertensive gastropathy than in noncirrhotics (P < 0.001), whereas the oxygen content of the gastric mucosa was similar in both groups. This pattern indicates that cirrhotics with portal hypertensive gastropathy have increased gastric perfusion without congestion. Gastric blood flow estimated by laser-Doppler was significantly higher in cirrhotics with portal hypertensive gastropathy than in noncirrhotics (P < 0.001). In cirrhotic patients, gastric areas with cherry red spots showed a significantly higher IHb ratio than areas with a mosaic or scarlatina pattern (P < 0.05). The magnitude of changes in gastric perfusion and the endoscopic severity of portal hypertensive gastropathy had no relationship with the degree of portal hypertension or the azygos blood flow.

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

The present study investigates the effects of acute normovolemic anemia induced by isovolemic hemodilution on gastric mucosal blood flow (GMBF), measured by hydrogen gas clearance, and on the oxygen and hemoglobin content in the gastric mucosa, estimated by reflectance spectrophotometry. GMBF significantly increased after 3 and 6 mL of isovolemic hemodilution (from 50 +/- 5 to 70 +/- 7 and 77 +/- 6 mL.min-1.100 g-1, respectively; P less than 0.05) compared with basal values (50 +/- 5.mL-1.min-1.100 g-1; P less than 0.05). Oxygen content remained unchanged, whereas hemoglobin concentration decreased in parallel with the decrease in hematocrit. In a second set of experiments, the role of endogenous nitric oxide (NO) as a possible mediator of the gastric vascular changes induced by hemodilution was investigated by using the specific inhibitor of NO biosynthesis, NG-monomethyl-L-arginine (L-NMMA). The increase in GMBF induced by 3 mL of isovolemic hemodilution (delta 23 +/- 7 mL.min-1.100 g-1) was attenuated in a dose-related manner with L-NMMA, 6.25 mg/kg IV (delta 15 +/- 4 mL.min-1.100 g-1) or 50 mg/kg IV (delta 5 +/- 2 mL.min-1.100 g-1 g; P less than 0.05). The concurrent administration of L-arginine (the precursor of NO biosynthesis) abolished the effects of L-NMMA on GMBF changes. The current findings show that acute normovolemic anemia causes an increase in GMBF that is dependent on the endogenous formation of NO.

Mechanisms responsible for enhanced inflammatory response to ischemia-reperfusion in diabetes

The objective of the present study was to assess the role of lipid mediators and adhesion molecule expression in exacerbation of ischemia-reperfusion-induced inflammatory response in diabetes. Leukocyte-endothelial cell interactions were studied in mesenteric venules by intravital microscopy. Endothelial expression of intercellular adhesion molecule (ICAM)-1 was measured by the double-radiolabeled monoclonal antibody technique, and beta2-integrin expression was measured by flow cytometry. Ischemia-reperfusion elicited significantly larger increases in leukocyte adhesion and emigration in diabetic rats that were prevented by a platelet-activating factor (PAF)-receptor antagonist or a leukotriene synthesis inhibitor. Leukotriene B4 (LTB4) superfusion induced similar leukocyte recruitment in diabetic and control rats, whereas PAF elicited larger increases in diabetic rats. CD11a, but not CD11b, expression was higher in leukocytes from diabetic animals. Endothelial ICAM-1 in mesentery and in intestine did not differ between diabetic and control rats. These results indicate that diabetes is associated with an enhanced response to ischemia-reperfusion that depends on both PAF and leukotrienes. An increased sensitivity to PAF, along with an increased CD11a expression, may account for the exaggerated inflammatory response to ischemia-reperfusion in diabetes.The objective of the present study was to assess the role of lipid mediators and adhesion molecule expression in exacerbation of ischemia-reperfusion-induced inflammatory response in diabetes. Leukocyte-endothelial cell interactions were studied in mesenteric venules by intravital microscopy. Endothelial expression of intercellular adhesion molecule (ICAM)-1 was measured by the double-radiolabeled monoclonal antibody technique, and β2-integrin expression was measured by flow cytometry. Ischemia-reperfusion elicited significantly larger increases in leukocyte adhesion and emigration in diabetic rats that were prevented by a platelet-activating factor (PAF)-receptor antagonist or a leukotriene synthesis inhibitor. Leukotriene B4(LTB4) superfusion induced similar leukocyte recruitment in diabetic and control rats, whereas PAF elicited larger increases in diabetic rats. CD11a, but not CD11b, expression was higher in leukocytes from diabetic animals. Endothelial ICAM-1 in mesentery and in intestine did not differ between diabetic and control rats. These results indicate that diabetes is associated with an enhanced response to ischemia-reperfusion that depends on both PAF and leukotrienes. An increased sensitivity to PAF, along with an increased CD11a expression, may account for the exaggerated inflammatory response to ischemia-reperfusion in diabetes.

INFLUENCE OF DOSE-RATE ON INFLAMMATORY DAMAGE AND ADHESION MOLECULE EXPRESSION AFTER ABDOMINAL RADIATION IN THE RAT

PURPOSE The goal of this study was to assess the effects of two clinically relevant radiation dose-rates on endothelial adhesion molecule expression, inflammatory response, and microvascular dysfunction. METHODS AND MATERIALS Rats were irradiated with 10 Gy at low (0.9 Gy/min) or high (3 Gy/min) dose-rates. Control animals received sham irradiation. Leukocyte rolling, adhesion, emigration, and microvascular permeability were assessed in mesenteric venules by intravital microscopy 6 hours after irradiation. P-selectin and intercellular adhesion molecule-1 (ICAM-1) expression were measured using radiolabeled monoclonal antibodies. RESULTS Low dose-rate (LDR) abdominal irradiation increased leukocyte adhesion compared with sham-irradiated animals, whereas high dose-rate (HDR) irradiation resulted in enhanced leukocyte rolling, adhesion, and emigration, compared with the LDR or with sham-irradiated rats. Both dose-rates increased microvascular permeability, although this effect was significantly greater after radiation with the high (8-fold) than the low (5-fold) dose-rate. HDR radiation induced significantly larger increments in P-selectin expression in splanchnic organs than LDR, whereas in most organs ICAM-1 expression was only upregulated by the HDR. Blockade of ICAM-1, but not P-selectin, abrogated leukocyte adhesion at both dose-rates. CONCLUSIONS The magnitude of upregulation of endothelial adhesion molecules, leukocyte recruitment, and endothelial barrier dysfunction elicited by radiation therapy is dependent on the dose-rate at which the radiation is delivered.

Anemia Worsens Hyperdynamic Circulation of Patients with Cirrhosis and Portal Hypertension

This retrospective cohort study was aimed atinvestigating the effects of anemia on the hemodynamicdisturbances associated with portal hypertension. Inall, 202 consecutive nontreated portal-hypertensive patients referred for evaluation to our HepaticHemodynamic Laboratory were included. Compared to thenonanemic patients, anemic cirrhotic patients had anincreased cardiac output (7.9 ± 1.9 vs 7.1± 2 liters/min, P < 0.01), and a decreased mean arterialblood pressure (82 ± 11 vs 94 ± 13 mm Hg,P < 0.0001) and systemic vascular resistance (838± 235 vs 1102 ± 356dyn/sec/cm5, P < 0.0001). Similar resultswere obtained when Child A or Child B-C patients were analyzedseparately. Multivariate logistic regression disclosedthat hemoglobin concentration, in addition to age, sexazygos blood flow, and albumin concentration, was anindependent factor influencing the degree of systemicvasodilation in cirrhotic portal-hypertensive patients.This study discloses that anemia worsens thehyperdynamic circulation associated with portalhypertension. Since hemoglobin concentration may change withtime, this parameter should be taken into account whenevaluating hemodynamics in portal-hypertensivepatients.

Mechanisms underlying the anti-inflammatory actions of central corticotropin-releasing factor

Immune activation of hypothalamic corticotropin-releasing factor (CRF) provides a negative feedback mechanism to modulate peripheral inflammatory responses. We investigated whether central CRF attenuates endothelial expression of intercellular adhesion molecule 1 (ICAM-1) and leukocyte recruitment during endotoxemia in rats and determined its mechanisms of action. As measured by intravital microscopy, lipopolysaccharide (LPS) induced a dose-dependent increase in leukocyte rolling, adhesion, and emigration in mesenteric venules, which was associated with upregulation of endothelial ICAM-1 expression. Intracisternal injection of CRF abrogated both the increased expression of ICAM-1 and leukocyte recruitment. Intravenous injection of the specific CRF receptor antagonist astressin did not modify leukocyte-endothelial cell interactions induced by a high dose of LPS but enhanced leukocyte adhesion induced by a low dose. Blockade of endogenous glucocorticoids but not α-melanocyte-stimulating hormone (α-MSH) receptors reversed the inhibitory action of CRF on leukocyte-endothelial cell interactions during endotoxemia. In conclusion, cerebral CRF blunts endothelial upregulation of ICAM-1 and attenuates the recruitment of leukocytes during endotoxemia. The anti-inflammatory effects of CRF are mediated by adrenocortical activation and additional mechanisms independent of α-MSH.Immune activation of hypothalamic corticotropin-releasing factor (CRF) provides a negative feedback mechanism to modulate peripheral inflammatory responses. We investigated whether central CRF attenuates endothelial expression of intercellular adhesion molecule 1 (ICAM-1) and leukocyte recruitment during endotoxemia in rats and determined its mechanisms of action. As measured by intravital microscopy, lipopolysaccharide (LPS) induced a dose-dependent increase in leukocyte rolling, adhesion, and emigration in mesenteric venules, which was associated with upregulation of endothelial ICAM-1 expression. Intracisternal injection of CRF abrogated both the increased expression of ICAM-1 and leukocyte recruitment. Intravenous injection of the specific CRF receptor antagonist astressin did not modify leukocyte-endothelial cell interactions induced by a high dose of LPS but enhanced leukocyte adhesion induced by a low dose. Blockade of endogenous glucocorticoids but not alpha-melanocyte-stimulating hormone (alpha-MSH) receptors reversed the inhibitory action of CRF on leukocyte-endothelial cell interactions during endotoxemia. In conclusion, cerebral CRF blunts endothelial upregulation of ICAM-1 and attenuates the recruitment of leukocytes during endotoxemia. The anti-inflammatory effects of CRF are mediated by adrenocortical activation and additional mechanisms independent of alpha-MSH.

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.

Gastric Mucosal Blood Flow Regulation in Response to Different Stimuli

We compared changes in gastric mucosal bloodflow (GMBF) and left gastric artery blood flow (LGABF)in response to pharmacological, physiological, andpathological stimuli. GMBF and LGABF were measured by the hydrogen gas clearance and perivascularultrasonic transit time techniques, respectively, underbaseline conditions and following intravenous infusionof vasopressin or pentagastrin, isovolemic hemodilution, or gastric perfusion with HCl-taurocholate.Blood flow changes following vasopressin or hemodilutionwere significantly larger in the left gastric arterythan in the gastric mucosa. In contrast, the increment in blood flow associated withpentagastrin-stimulated acid secretion was significantlygreater in the gastric mucosa than in the extramuralartery. Barrier disruption with acid-taurocholateinduced similar changes in both measurement sites. The gastrichyperemia induced by either mechanism was significantlyattenuated by blockade of NO synthesis. These datademonstrate that although functional changes in GMBF are primarily supported by changes inblood flow at the extramural gastric arteries, thegastric mucosal microvasculature is also under theinfluence of independent local controlmechanisms.

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.