Monoclonal antibody to L-selectin attenuates neutrophil accumulation and protects ischemic reperfused cat myocardium

BACKGROUND

Interaction of CD11/CD18 located on neutrophil membranes with its endothelial counter-receptor, intercellular adhesion molecule-1, plays a major role in polymorphonuclear leukocyte (PMN)-mediated endothelial dysfunction and myocardial injury associated with ischemia and reperfusion. However, PMN-derived L-selectin, which is thought to play an early role in PMN rolling along the vascular endothelium, has not been studied in a setting of myocardial ischemia and reperfusion.

METHODS AND RESULTS

In this study, we evaluated the effects of a monoclonal antibody against L-selectin, DREG-200, in a feline model of myocardial ischemia (1.5 hours) and reperfusion (4.5 hours). DREG-200 (1 mg/kg) or an isotype-matched IgG1 antibody, MAb R3.1, which does not cross-react in cats, was administered as a bolus 10 minutes before reperfusion. In MAb R3.1-treated cats, myocardial ischemia followed by reperfusion resulted in significant coronary vascular endothelial dysfunction, elevated cardiac myeloperoxidase activity indicative of neutrophil accumulation in the ischemic myocardium, and severe myocardial injury. In contrast, administration of DREG-200 at 1 mg/kg significantly attenuated myocardial necrosis (14 +/- 4 versus 32 +/- 3 expressed as percentage of area at risk, P < .001) and attenuated coronary endothelial dysfunction (P < .01) associated with ischemia/reperfusion. Moreover, myeloperoxidase activity in the ischemic myocardium was significantly lower than MAb R3.1-treated cats (0.4 +/- 0.1 versus 0.9 +/- 0.2 U/100 mg tissue, P < .05).

CONCLUSIONS

These results demonstrate that blocking L-selectin with DREG-200 exerts a significant cardioprotective effect in a feline model of myocardial ischemia and reperfusion, indicating that L-selectin plays a significant role in mediating PMN accumulation and PMN-induced endothelial and myocardial injury after ischemia and reperfusion.

Decreased basal nitric oxide release in hypercholesterolemia increases neutrophil adherence to rabbit coronary artery endothelium

Hypercholesterolemia, before atherosclerosis, is known to reduce agonist- (e.g., acetylcholine) mediated nitric oxide (NO) production within 2 weeks of a cholesterol-enriched diet. However, no data exist on the effect of hypercholesterolemia on the basal release of NO from blood vessels. We studied the basal release of NO in rabbit coronary arteries by addition of the NO synthase blocker NG-nitro-L-arginine-methyl ester (L-NAME). Basal release of NO was markedly attenuated 2 weeks after introduction of a 0.5% cholesterol addition to the diet. One week later, the adherence of neutrophils to the coronary endothelium was significantly enhanced (i.e., threefold; p < 0.01 different from control). The increased adhesiveness could be attributed to enhanced endothelial adhesion rather than to changes in the properties of the leukocytes. Both phenomena could be reversed by addition of L-arginine to isolated coronary arteries. Administration of 10 mg/day lovastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, markedly attenuated both the reduced basal NO production and the increased adhesiveness of the endothelium. These results support the concept that NO is an important protective agent produced by the endothelium to preserve the integrity of the endothelium and may protect it against atherogenesis.

Diminished basal nitric oxide release after myocardial ischemia and reperfusion promotes neutrophil adherence to coronary endothelium

We measured changes in basal release of nitric oxide and its effect on polymorphonuclear leukocyte (PMN) adherence to endothelial cells (ECs) in a feline model of myocardial ischemia (90 minutes) and reperfusion. Basal release of nitric oxide from the left anterior descending coronary artery (LAD) after myocardial ischemia/reperfusion and from the control left circumflex coronary artery (LCX) was assessed by NG-nitro L-arginine methyl ester (L-NAME)-induced vasocontraction. L-NAME induced a significant EC-dependent vasocontraction in control LCX rings (0.28 +/- 0.04 g), which was fully reversed by L-arginine but not D-arginine. L-NAME-induced vasocontraction of LAD rings was not significantly changed after 90 minutes of myocardial ischemia without reperfusion. However, 10 minutes of reperfusion reduced the L-NAME-induced vasocontraction to 0.13 +/- 0.04 g (p < 0.05), and this was restored by addition of 3 mM L-arginine but not D-arginine. Longer periods of reperfusion progressively decreased L-NAME-induced vasocontraction. After 270 minutes of reperfusion, L-NAME-induced vasocontraction was virtually abolished. Myocardial ischemia without reperfusion did not increase PMN adherence to ECs. However, PMN adherence to LAD ECs was significantly increased after 20 minutes of reperfusion (39 +/- 6 to 105 +/- 9 PMNs/mm2, p < 0.01), and incubation of LAD segments with L-arginine significantly attenuated this increase in PMN adherence. After 270 minutes of reperfusion, PMN adherence to LAD ECs was further increased to 224 +/- 10 PMNs/mm2 (p < 0.001). This increase in PMN adherence was almost completely blocked by MAb R15.7, a monoclonal antibody against CD18 of PMNs, and was significantly attenuated by MAb RR1/1, a monoclonal antibody against intercellular adhesion molecule-1 of ECs (p < 0.01). These results indicate that decreased basal release of endothelium-derived relaxing factor after myocardial ischemia/reperfusion precedes enhanced PMN adherence to the coronary endothelium, which may lead to PMN-induced myocardial injury.

Mechanism of the cardioprotective effect of transforming growth factor beta 1 in feline myocardial ischemia and reperfusion

We studied the effects of transforming growth factor beta 1 (TGF-beta 1) in a feline model of myocardial ischemia (1.5 hr) and reperfusion (4.5 hr). Myocardial ischemia followed by reperfusion resulted in severe myocardial injury, endothelial dysfunction, high cardiac myeloperoxidase activity indicative of neutrophil accumulation in the ischemic myocardium, and significant neutrophil adherence to the ischemic coronary endothelium. In contrast, intravenous administration of TGF-beta 1 (20 micrograms/kg) 30 min prior to reperfusion significantly attenuated myocardial necrosis (13.8% +/- 3.5% vs. 32.2% +/- 2.9% of area-at-risk, P < 0.01) and attenuated endothelial dysfunction (P < 0.01) associated with ischemia-reperfusion. Moreover, myeloperoxidase activity in the ischemic myocardium was significantly lower than vehicle controls (0.2 +/- 0.1 vs. 1.7 +/- 0.3 units/100 mg of tissue, P < 0.01) and neutrophil adherence to ischemic coronary endothelium was significantly (P < 0.01) attenuated in TGF-beta 1-treated cats. These results demonstrate that TGF-beta 1 exerts a significant cardioprotective effect in a feline model of myocardial ischemia and reperfusion. The mechanism of this protective effect appears to relate to endothelial preservation by TGF-beta 1 inhibiting circulating neutrophils from adhering to the endothelium, a critical step in neutrophil-induced reperfusion injury.

Cytokines and growth factors in endothelial dysfunction

OBJECTIVE

The purpose of this focused review is to call attention to the important interrelationships between growth factors (e.g., transforming growth factor-beta) and cytokines (e.g., tumor necrosis factor [TNF]) on endothelial function as characterized by the ability of the endothelium to release endothelium-derived relaxing factor.

BACKGROUND AND METHODS

Myocardial ischemia followed by reperfusion leads to a severe degree of endothelial dysfunction characterized by an impaired vasodilator response to endothelial-dependent vasodilators. The reduction in endothelial-dependent responses occurs rapidly after the onset of reperfusion. Endothelial dysfunction was studied in coronary artery as well as superior mesenteric artery rings, and the effects of cytokines, transforming growth factor-beta, and free radicals were assessed.

RESULTS

Oxygen-derived free radicals (i.e., superoxide anion) and cytokines (i.e., TNF) contribute to this endothelial dysfunction, which is characterized by a loss of endothelium-derived relaxing factor, now known to be identical to nitric oxide. Agents such as superoxide dismutase or transforming growth factor-beta can significantly preserve endothelial integrity during ischemia-reperfusion states.

CONCLUSIONS

Endothelial dysfunction is an early and critical phenomenon occurring in ischemia-reperfusion injury both in the coronary and the mesenteric circulations.

Protective actions of S-nitroso-N-acetylpenicillamine (SNAP) in a rat model of hemorrhagic shock

The anti-shock effects of an organic nitric oxide donor, S-nitroso-N-acetylpenicillamine (SNAP), were tested in a rat model of hemorrhagic shock. Administration of SNAP at a dose of 10 mcg/kg injection followed by 10 mcg/kg/h infusion neither significantly decreased mean arterial blood pressure (MABP) nor significantly altered bleedout volumes in hemorrhagic rats, indicating that SNAP did not modify the severity of the shock protocol. However, hemorrhaged rats treated with SNAP maintained post-reinfusion MABP at significantly higher values than hemorrhaged rats receiving 0.9% NaCl (final MABP 81 +/- 3.0 mmHg vs. 54 +/- 1.1 mmHg, respectively; p < 0.001). SNAP also significantly increased survival times following hemorrhagic shock (113 +/- 4 min in SNAP treated rats compared with 70 +/- 4.5 min in vehicle treated rats, p < 0.001). The overall survival rates were 87.5% when treated with SNAP and 0% with 0.9% NaCl (p < 0.01). In hemorrhagic shock rats receiving only vehicle, a significant accumulation of neutrophils in intestinal tissue occurred as indicated by a higher MPO activity in intestinal tissue (MPO activity, 1.26 +/- 0.31 vs. 0.14 +/- 0.05U/100 mg in sham hemorrhagic shock rats, p < 0.02). Administration of SNAP significantly attenuated the neutrophil accumulation in the intestinal tissue (MPO activity, 0.42 +/- 0.09U/100 mg, p < 0.05 compared with hemorrhagic rats receiving only the vehicle). Moreover, endothelial dysfunction of superior mesenteric artery rings occurred in hemorrhagic shock rats given only 0.9% NaCl.(ABSTRACT TRUNCATED AT 250 WORDS)

Antishock and endothelial protective actions of a NO donor in mesenteric ischemia and reperfusion

Splanchnic artery occlusion (SAO) of the celiac, superior mesenteric, and inferior mesenteric arteries for 2 hr, followed by a 2-hr reperfusion period in cats produces a severe form of circulatory shock characterized by endothelial dysfunction, increased lysosomal leakage, and severe hypotension resulting from release of proteases, oxygen-derived free radicals, and other humoral mediators into the circulation. Administration of 0.75 mg/kg/hr of C873754, a nitric oxide (NO) donor, 10 min prior to reperfusion, significantly attenuated the accumulation of plasma cathepsin D from 12 +/- 3 U/ml in the SAO + vehicle group to 5 +/- 1 U/ml (P < 0.05) in the C87-3754 treated SAO group. A similar attenuation of plasma myocardial depressant factor (MDF) activity was observed in the C87-3754 treated cats (P < 0.02). Administration of C87-3754 significantly increased short term (i.e., 2-hr) survival rate (P < 0.05, compared to the vehicle group). Moreover, C87-3754 attenuated the SAO shock induced decline in release of endothelium-derived relaxing factor (EDRF) from isolated superior mesenteric artery (SMA) rings stimulated by acetylcholine and A23187. Additionally, C87-3754 significantly decreased PMN adherence to the superior mesenteric venous endothelium in vitro. Thus, treatment with the NO donor, C87-3754 reduced the accumulation of humoral mediators into the plasma while significantly attenuating endothelial dysfunction and improving short term survival.

Coronary endothelial and cardiac protective effects of a monoclonal antibody to intercellular adhesion molecule-1 in myocardial ischemia and reperfusion

BACKGROUND

Intercellular adhesion molecule-1 (ICAM-1) is a major ligand on endothelial cells for adherence of activated polymorphonuclear leukocytes (PMNs). The major purpose of this study was to study the effects of RR1/1, a monoclonal antibody against ICAM-1 (i.e., MAb RR1/1), on myocardial injury and endothelial dysfunction associated with myocardial ischemia and reperfusion.

METHODS AND RESULTS

Either MAb RR1/1 (2 mg/kg, n = 7), an antibody that was found to bind selectively to endothelial cells in the cat, or MAb R3.1 (2 mg/kg, n = 7), a nonbinding control antibody, was given as an intravenous bolus 10 minutes before reperfusion. Two hundred eighty minutes later, hearts were excised. The left ventricle area-at-risk (AAR) was similar in MAb RR1/1 (29 +/- 2%) and MAb R3.1 (30 +/- 3%) groups. In MAb R3.1-treated cats, 90 minutes of myocardial ischemia plus 4.5 hours of reperfusion induced a significant myocardial injury (necrotic tissue/AAR, 28 +/- 2%), high myeloperoxidase activity (0.65 +/- 0.16 units/100 mg ischemic tissue), and a marked decrease in endothelium-dependent vasorelaxation in isolated left anterior descending coronary arteries (vasorelaxation to acetylcholine, 29 +/- 3%) with no change in endothelium-independent vasorelaxation (relaxation to NaNO2, 91 +/- 3%). However, cats treated with MAb RR1/1 developed significantly less myocardial necrosis (10 +/- 2% of the AAR, p less than 0.01), lower myeloperoxidase activity in ischemic myocardial tissue (0.2 +/- 0.03 units/100 mg ischemic tissue, p less than 0.01), and enhanced vasorelaxant responses to endothelial-dependent relaxation to acetylcholine (53 +/- 5%) compared with ischemic/reperfused cats treated with Mab R3.1. Furthermore, addition of MAb RR1/1 in vitro significantly inhibited unstimulated PMN adherence to ischemic-reperfused coronary artery endothelium.

CONCLUSIONS

These results suggest that ICAM-1-dependent PMN adherence plays an important role in reperfusion injury, and that PMN adherence and infiltration contribute significantly to coronary endothelial dysfunction.

Beneficial effects of SPM-5185, a cysteine-containing NO donor in myocardial ischemia-reperfusion

Intravenous administration of SPM-5185 [N-nitratopivaloyl-S-(N'-acetylalanyl)-cysteine ethyl ester], a cysteine-containing nitric oxide (NO) donor, or SPM-5267 [pivaloyl-S-(N'-acetylalanyl)-cysteine ethyl ester], an analogue of SPM-5185 that lacks the NO moiety, was studied in a feline myocardial ischemia-reperfusion model. Administration of SPM-5185 (1 mg/kg), followed by a 2-mg.kg-1.h-1 infusion starting 10 min before reperfusion, resulted in significant protection 4.5 h postreperfusion. In the myocardial ischemia (MI)+SPM-5267 group, 38 +/- 4% of the area at risk was necrotic, whereas the necrotic area/area at risk was only 7 +/- 2% in the MI+SPM-5185 group (P less than 0.01). Moreover, SPM-5185 treatment markedly attenuated the endothelial dysfunction observed in the left anterior descending coronary artery after reperfusion by 50%. These beneficial effects occurred despite the absence of a significant change in myocardial oxygen demand, as measured by the pressure-rate index. In vitro experiments demonstrated that SMP-5185, but not SPM-5267, decreased adherence of neutrophils to the coronary vascular endothelium and decreased production of superoxide radicals. Therefore, a likely mechanism of the observed cardioprotection by SPM-5185 involves attenuation of polymorphonuclear leukocyte-induced endothelial dysfunction.

Cardiac venous endothelial dysfunction after myocardial ischemia and reperfusion in dogs

Endothelial dysfunction is a prominent occurrence in coronary arteries after myocardial ischemia and reperfusion. However, this has not been studied in coronary veins. Endothelium-dependent vasorelaxation was studied in cardiac venous rings obtained from dogs subjected to 60 min of coronary artery occlusion followed by 270 min of reperfusion, as well as from dogs subjected to sham ischemia-reperfusion. Myocardial ischemia resulted in a 96 +/- 2% decrease in coronary flow to the ischemic area 60 min after occlusion of the left anterior descending (LAD) coronary artery, which led to a significant degree of cardiac necrosis (i.e., 32.9 +/- 3.9% of area at risk). Cardiac venous rings isolated from sham ischemia-reperfusion dogs relaxed 68 +/- 3% to 200 microM ADP, 65 +/- 3% to 2 microM A23187, and 76 +/- 4% to 200 microM sodium nitrite (NaNO2). Corresponding values for cardiac venous rings isolated from ischemic-reperfused dogs were 32 +/- 3% for 200 microM ADP (P less than 0.01 vs. sham), 31 +/- 3% for 2 microM A23187 (P less than 0.01 vs. sham), and 74 +/- 3% for 200 microM NaNO2 (NS from sham). In rings from control dogs, vasorelaxation to ADP and A23187 was markedly inhibited by 4 mM NG-methyl-L-arginine (L-NMMA) and 10 methylene blue and restored after NG-nitro-L-arginine by 3 mM L-arginine. These results demonstrate that a significant degree of endothelial dysfunction occurred in cardiac venous rings after ischemia and reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Method of acetaldehyde measurement with minimal artifactual formation in red blood cells and plasma of actively drinking subjects with alcoholism

After alcohol consumption, a substantial amount of acetaldehyde that is reversibly bound to protein and nonprotein components of the red blood cells circulates in the blood and could cause extrahepatic toxicity. However, acetaldehyde measurement in human red blood cells is hampered by considerable ex vivo artifactual formation as a result of nonenzymatic oxidation of ethanol during protein precipitation. To eliminate this source of artifactual formation, free and reversibly bound acetaldehyde were trapped with semicarbazide from red blood cell hemolysates, and both the stroma and the hemoglobin were sequentially removed by centrifugation and ion-exchange chromatography in carboxymethyl Sephadex, respectively. The eluted semi-carbazone was dissociated with perchloric acid, and the acetaldehyde that was released in the protein-free supernatants was measured by head-space gas chromatography. Maximal retention of hemoglobin by carboxymethyl Sephadex and complete recovery of acetaldehyde and ethanol were achieved at a pH of 5.3. The artifactual formation decreased from 2.62 +/- 0.32 mumol of acetaldehyde per millimole of ethanol in the initial hemolysates to 1.38 +/- 0.20 mumol after removal of the stroma and to a level that is comparable to measurements in plasma (0.09 +/- 0.02 mumol) after removal of both the stroma and the hemoglobin. In 12 actively drinking subjects with alcoholism, with blood ethanol levels that ranged between 9 and 81 mmol/L, the concentrations of acetaldehyde in red blood cells (11.50 +/- 1.46 mumol/L; range: 7.5 to 22 mumol/L) were minimally affected by blood ethanol levels and were three times as high as those in the plasma (3.74 +/- 1.49 mumol/L).(ABSTRACT TRUNCATED AT 250 WORDS)

The role of L-arginine in ameliorating reperfusion injury after myocardial ischemia in the cat

BACKGROUND

Myocardial ischemia followed by reperfusion results in endothelial dysfunction characterized by a reduced release of endothelium-derived relaxing factor (EDRF). Because EDRF has been characterized as nitric oxide, we examined the ability of L-arginine, the substrate for nitric oxide synthesis, to protect in a feline model of myocardial ischemia plus reperfusion.

METHODS AND RESULTS

The effects of L-arginine were investigated in a 6-hour model of myocardial ischemia and reperfusion in pentobarbital-anesthetized cats. A bolus administration (30 mg/kg) of L-arginine, or its enantiomer D-arginine, was given followed by a continuous infusion of 10 mg/kg/min for 1 hour starting 10 minutes before reperfusion. Myocardial ischemia plus reperfusion in cats receiving D-arginine resulted in severe myocardial injury and endothelial dysfunction characterized by marked myocardial necrosis, high cardiac myeloperoxidase activity in ischemic cardiac tissue, and loss of acetylcholine- and A-23187-induced endothelium-dependent relaxation in coronary artery rings. In contrast, myocardial ischemia plus reperfusion cats treated with L-arginine exhibited a reduced area of cardiac necrosis (16 +/- 2% versus 41 +/- 5% of area at risk, p less than 0.01), lower myeloperoxidase activity in the ischemic region (0.3 +/- 0.08 versus 0.8 +/- 0.10 units/100 mg tissue, p less than 0.05), and significant preservation of acetylcholine- (p less than 0.01) and A-23187- (p less than 0.01) induced endothelial-dependent relaxation.

CONCLUSIONS

These results demonstrate the ability of L-arginine to reduce necrotic injury in a cat model of myocardial ischemia plus reperfusion, and this reduction in infarct size is associated with the preservation of endothelial function and attenuation of neutrophil accumulation in ischemic cardiac tissue.

Activated neutrophils aggravate endothelial dysfunction after reperfusion of the ischemic feline myocardium

Endothelial dysfunction, as evidenced by decreased stimulated release of endothelium-derived relaxing factor (EDRF), occurs after reperfusion of the ischemic myocardium. To better understand this endothelial dysfunction, isolated cat hearts were perfused under constant flow by the Langendorff procedure with Krebs-Henseleit solution devoid of blood cells. Following global ischemia (90 minutes) and reperfusion (20 minutes), coronary vasorelaxation to the endothelium-dependent vasodilator acetylcholine (ACh) was 70 +/- 3% of initial values (p less than 0.01) compared with 90 +/- 4% in nonischemic control perfused hearts. No decrement occurred in response to the endothelium-independent vasodilator nitroglycerin (NTG). Coronary artery rings isolated from the ischemic left circumflex coronary artery showed a similar degree of endothelial dysfunction to ACh, with normal relaxation in response to NaNO2. Autologous cat neutrophils (100 million cells), activated with 100 nmol/L f-met-leu-phe infused into the heart directly before and throughout reperfusion, resulted in a further decrement in ACh-induced vasodilation, to 55 +/- 5% of initial response, with no effect on NTG-induced vasodilation. Similar results were obtained with coronary artery rings isolated from perfused cat hearts and exposed to neutrophils. This neutrophil-enhanced endothelial dysfunction was inhibited by human superoxide dismutase as well as by an antibody to the adherence glycoprotein complex CD-18 (i.e., MAbR 15.7). Therefore endothelial dysfunction occurs initially upon reperfusion of the previously ischemic heart and is aggravated by superoxide radicals produced by activated neutrophils.

Anti-ischaemic and endothelial protective actions of recombinant human osteogenic protein (hOP-1)

Osteogenic protein one (hOP-1), a member of the transforming growth factor-beta (TGF-beta) supergenic family, was studied for its anti-ischaemic properties in rats subjected to myocardial ischaemia and reperfusion. Ten minutes after ligation (i.e., just prior to reperfusion) of the left coronary artery, 2 or 20 micrograms/rat recombinant human (hOP-1) or its vehicle, was given intravenously. hOP-1 at 20 micrograms significantly reduced reperfusion injury 24 h later compared to rats receiving only vehicle (i.e., 0.9% NaCl). hOP-1 was also found to preserve rat coronary endothelial function (i.e., release of endothelium-derived relaxing factor, EDRF) in perfused hearts following global ischaemia and reperfusion. Moreover, hOP-1 also significantly inhibited adherence of rat neutrophils to rat vascular endothelium in vitro. Thus, hOP-1 exerts significant anti-ischaemic effects. Some of this cardioprotection may be related to the ability of hOP-1 to preserve endothelial function and inhibit neutrophil adherence to the endothelium.

Splanchnic vascular endothelial dysfunction in rat endotoxemia: role of superoxide radicals

Intravenous lipopolysaccharide, 30 mg/kg, results in rapid systemic hypotension in anesthetized rats. Interaction of lipopolysaccharide with the vascular endothelium and blood borne cells results in the elaboration of cytokines and oxygen-derived free radicals, all of which can be injurious to normal endothelial function. To evaluate endothelial function, superior mesenteric artery rings were isolated from endotoxemic rats just prior to death. Endotoxemia significantly blunted superior mesenteric artery ring vasorelaxations to acetylcholine and to A23187 but not to NaNO2. Contraction of superior mesenteric artery rings from endotoxemic rats induced by U46619 was not altered. Treatment with human superoxide dismutase or U74006F, an aminosteroid, significantly preserved vasorelaxation to acetylcholine and A23187. However, the hydroxyl radical scavenger N-(2-mercaptopropionyl)-glycine did not protect the endothelium. Thus, intravenous lipopolysaccharide can induce endothelial dysfunction in superior mesenteric artery rings. Furthermore, because superoxide dismutase but not N-(2-mercaptopropionyl)-glycine preserves endothelial function, it is likely that superoxide radicals mediate the endothelial dysfunction observed in endotoxemic rats.

Mechanisms of the cardioprotective actions of WEB-2170, bepafant, a platelet activating factor antagonist, in myocardial ischemia and reperfusion

The cardioprotective effects of WEB-2170, a specific platelet activating factor (PAF) receptor antagonist, were investigated in a feline model of myocardial ischemia (MI) and reperfusion. Either WEB-2170 (1-mg/kg bolus plus 2 mg/kg/hr) or its vehicle (0.9% NaCl) was administered 1 hr after left anterior descending coronary artery occlusion (i.e., 30 min before reperfusion). The cardiac area-at-risk (AAR) was similar in MI-reperfused (MI + R) cats given either WEB-2170 (31.5 +/- 3.6%) or vehicle (27.8 +/- 2.8%). However, in cats receiving only the vehicle, 1.5 hr of ischemia plus 4.5 hr of reperfusion resulted in significant myocardial injury (necrotic tissue/AAR, 37.7 +/- 4.5%), high plasma creatine kinase activity (29.4 +/- 4.1 I.U./micrograms of protein) and a marked decrease in endothelium-dependent relaxation in isolated left anterior descending coronary arteries to acetylcholine (33 +/- 4% of U-46619-induced vasocontraction) with no change in endothelium-independent relaxation to NaNO2 (91 +/- 1%). In contrast, MI + R cats treated with WEB-2170 developed significantly less myocardial necrosis (necrotic tissue/AAR, 12.0 +/- 2.8%, P less than .001), lower plasma creatine kinase activity (16.5 +/- 4.1 I.U./micrograms of protein, P less than .01) and enhanced vascular relaxation to acetylcholine (53 +/- 4.1%, P less than .01) compared to MI + R cats given only the vehicle. Furthermore, the addition of WEB-2170 to PMN suspensions in vitro significantly inhibited (P less than .01) PAF-induced polymorphonuclear leukocyte (PMN) adherence to endothelial cells (12 +/- 2.4 cells/field vs. 27 +/- 2.6 in the control group).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardioprotection and attenuation of endothelial dysfunction by organic nitric oxide donors in myocardial ischemia-reperfusion

The effects of two nitric oxide (NO) donors were evaluated in a 6-h model of feline myocardial ischemia-reperfusion. After 80 min of a 90-min ischemic period, SIN-1 or C87-3754 or their respective controls (i.e., 0.9% NaCl or C88-3934, a control compound which does not release NO) were given i.v. as a bolus (0.1 mg/kg) and infused at 1 mg/kg/h for the entire 4.5-h reperfusion period. Administration of the active NO donors significantly decreased the necrotic area/area-at-risk ratio from 29 +/- 3% in the vehicle group to 9 +/- 2 and 11 +/- 5% in the SIN-1 and C87-3754 groups, respectively (P less than .001). The inactive NO donor C88-3934 failed to reduce infarct size (31 +/- 3%). Neither NO donor reduced the accumulation of neutrophils in the necrotic area when compared to their respective control groups, but both agents significantly attenuated coronary endothelial dysfunction as shown by a vasorelaxation to acetylcholine of 62 +/- 2 and 64 +/- 3% in the SIN-1- and C87-3754-treated arteries, as compared to only a 27 +/- 3 and 34 +/- 4% vasorelaxation in the vehicle and inactive NO donor groups, respectively (P less than .001). Our studies show that SIN-1 and C87-3754 exert beneficial effects in a 6-h model of myocardial ischemia-reperfusion. Both NO donors decreased myocardial necrosis and decreased the reperfusion-induced endothelial dysfunction without significantly altering the pressure-rate index (i.e., an index of myocardial oxygen demand).

Low doses of superoxide dismutase and a stable prostacyclin analogue protect in myocardial ischemia and reperfusion

The effects of low dose human superoxide dismutase and low dose taprostene, a stable analogue of prostacyclin, were investigated separately and together in a model of myocardial ischemia (1.5 h) with reperfusion (4.5 h) in open chest, anesthetized cats. Taprostene (60 ng/kg per min), human superoxide dismutase (0.25 mg/kg per h), both agents together, or their vehicle, were infused intravenously in cats starting 0.5 h after occlusion of the left anterior descending coronary artery. Neither low dose taprostene nor low dose human superoxide dismutase exerted any endothelial or myocardial protection in this model. However, the two agents together showed a significant endothelial and myocardial protection in cats with myocardial ischemia and reperfusion. Compared with cats that were untreated or received only taprostene or human superoxide dismutase, cats receiving both agents exhibited a lower plasma creatine kinase activity at every time point observed after reperfusion, a reduced area of cardiac necrosis (7 +/- 2% vs. 21 +/- 5% area at risk, p less than 0.001), lower myeloperoxidase activity in the ischemic region (p less than 0.01) and a significant preservation of vasorelaxant responses of left anterior descending coronary rings to endothelium-dependent vasodilators, acetylcholine (p less than 0.001) and A-23187 (p less than 0.001). Taprostene appears to act additively with human superoxide dismutase to inhibit neutrophil adherence and activation and to inactivate superoxide radicals, and thus reduce cellular injury 4.5 h after reperfusion of the ischemic heart. Use of this agent may allow low doses of superoxide dismutase to be used more effectively in early myocardial ischemia.

Novel beneficial mechanisms of defibrotide, a prostacyclin enhancing agent in splanchnic artery occlusion and reperfusion in rats

To further clarify the protective mechanism(s) of defibrotide in splanchnic artery occlusion (SAO) shock, we observed the effect of defibrotide on polymorphonuclear leukocyte (PMN) accumulation in the intestinal tissue, gastric lysosomal hydrolases and endothelial function of the ischemia-reperfused superior mesenteric artery (SMA). Pentobarbital anesthetized rats were subjected to occlusion of both the celiac and superior mesenteric arteries for 90 min followed by 2 h reperfusion. The rats receiving only the vehicle for defibrotide exhibited a marked increase in intestinal myeloperoxidase (MPO) activity and a significant endothelial dysfunction manifested by the loss of endothelium-dependent vasorelaxation. Only 2 of 6 rats (33%) survived 2 h of reperfusion. In contrast, those rats treated with defibrotide exhibited significantly attenuated PMN accumulation in intestinal tissue, enhanced endothelium-dependent vasorelaxation in SMA rings, prolonged survival time and increased survival rate to 6 of 7 (i.e., 86%). However, addition of defibrotide in vitro had no direct effect on LTB4 activated PMN adherence to vascular endothelium. Moreover, defibrotide preserved gastric lysosomal membranes in vitro. These results indicate that the protective effect of intravenous administration of defibrotide on SAO shock may be related to its endothelial preserving effect reducing PMN adherence and protection of endothelial and lysosomal membrane integrity.

Antibody to CD-18 exerts endothelial and cardiac protective effects in myocardial ischemia and reperfusion

We studied the effects of MAbR15.7, an antibody directed against the common beta-chain (CD-18) of a family of neutrophil adherence glycoproteins, on endothelial dysfunction and myocardial injury in a model of myocardial ischemia and reperfusion in cats. Pentobarbital-anesthetized cats were subjected to 1.5 h occlusion of the left anterior descending coronary artery (LAD) and 4.5 h of reperfusion. MI + R resulted in severe myocardial injury and endothelial dysfunction, including significant elevation of plasma creatine kinase (CK) activity, marked myocardial necrosis, high cardiac myeloperoxidase (MPO) activity in ischemic cardiac tissue, and loss of response of LAD coronary rings to the endothelium-dependent vasodilators, acetylcholine (ACh) and A-23187. In contrast, MAbR15.7-treated cats exhibited a lower plasma CK activity at every time point observed after 2 h, a reduced area of cardiac necrosis (2 +/- 1 vs. 30.8 +/- 2.5% of area-at-risk, P less than 0.001), lower MPO activity in the ischemic region (P less than 0.01), and significantly preserved vasorelaxant responses of LAD coronary rings to endothelium-dependent vasodilators, ACh (P less than 0.001), and A-23187 (P less than 0.001). These results indicate that myocardial ischemia and reperfusion induces significant myocardial injury and endothelial dysfunction in the cat involving a CD18-dependent neutrophil adherence mechanism. Inhibition of neutrophil adherence to the endothelium exerts significant protective effects in this model of reperfusion injury.

Gender differences in the response of hepatic fatty acids and cytosolic fatty acid-binding capacity to alcohol consumption in rats

To investigate possible gender differences in the response of hepatic fatty acids and cytosolic fatty acid-binding capacity to ethanol consumption, both female and male rats (41 days of age) were pair fed liquid diets (with a littermate of the same sex) for 28 days. The diets contained 36% of energy either as ethanol or as additional carbohydrate. After ethanol feeding, the hepatic concentration of fatty acids increased 155% in females (P less than 0.01), whereas there was only a trend for an increase (22%) in males. This was associated with a much smaller increase of cytosolic fatty acid-binding capacity in females (58%) than in males (161%). Whereas the ethanol-induced increase in fatty acid-binding capacity provided an ample excess of binding sites for the fatty acids in males, the increase in females was barely sufficient for the binding of the large increase of fatty acids produced by ethanol in the females. The cytosolic protein responsible for this binding, the liver fatty acid-binding protein of the cytosol (L-FABPc), also promotes esterification of the fatty acids. In keeping with the postulated role of this protein, the ethanol-induced increases in hepatic triacylglycerols, phospholipids, and cholesterol esters were smaller in females than in males. The gender difference in cholesterol esters was associated with parallel changes in acyl-CoA transferase activity. A possible implication of the relatively small and most likely inadequate increase in liver fatty acid-binding capacity and fatty acid esterification during alcohol consumption in the females is that under these circumstances the risk for development of a potentially deleterious accumulation of fatty acids in the liver is increased, thereby contributing to the enhanced vulnerability of females to alcohol-induced hepatotoxicity.

Time course of endothelial dysfunction and myocardial injury during coronary arterial occlusion

The time course of the effects of permanent myocardial ischemia without reperfusion on the coronary vascular endothelium and myocardium were investigated in anesthetized cats. The left anterior descending (LAD) coronary artery was occluded for 1.5, 3.0, 4.5, or 6.0 h. Coronary rings from the ischemic LAD and the nonischemic left circumflex (LCX) arteries were tested for their responsiveness to the endothelium-dependent vasodilators acetylcholine (ACh, 0.1-100 nM) and the calcium ionophore A23187 (1-1,000 nM), and the endothelium-independent vasodilator sodium nitrite (NaNO2, 0.1-100 microM). Vasorelaxation was not significantly impaired in response to ACh after 1.5 h of ischemia and only moderately impaired after 3.0 h of ischemia (63 +/- 5% of control). However, after 4.5 h of ischemia the ACh-induced response was decreased to 33 +/- 4% of control and further declined to 31 +/- 4% of control after 6.0 h (P less than 0.001 from 1.5 h). There was no significant decrease in LCX ring vasorelaxant responses to vasodilators at all times, and the LAD rings only showed a moderately decreased response to NaNO2 after 6.0 h of ischemia (82 +/- 4% relaxation, P less than 0.05). Transmission electron microscopy revealed very little endothelial damage at 4.5 and 6.0 h, with only some subendothelial swelling noted. Damage to the myocardium did not become significant until after 4.5 h of ischemia, and cardiac myeloperoxidase activity, indicative of neutrophil accumulation, was not significant at any time.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective actions of a leukotriene B4 antagonist in splanchnic ischemia and reperfusion in rats

Pentobarbital-anesthetized rats were subjected to occlusion of both the celiac and superior mesenteric arteries for 90 min followed by reperfusion for 2 h. All seven rats given only the vehicle died within 2 h of reperfusion, whereas rats treated with LY-255283 (3 or 10 mg/kg iv), a leukotriene B4 (LTB4) receptor antagonist given 10 min before reperfusion, exhibited significantly higher survival rates of 57% (4 out of 7) and 75% (6 out of 8), respectively, 2 h after reperfusion. Rats given 1 mg/kg of LY-255283 showed no significant improvement in survival. Splanchnic artery occlusion (SAO)-shock rats treated with LY-255283 (3 or 10 mg/kg) exhibited significantly attenuated accumulation of plasma free amino-nitrogenous compounds and of a myocardial depressant factor. Treatment with LY-255283 (10 mg/kg) markedly (P less than 0.01) ameliorated the deficits of endothelium-dependent relaxation of isolated superior mesenteric artery (SMA) rings in untreated SAO-shock rats. LY-255283 at 10 mg/kg significantly attenuated the increased myeloperoxidase activity in the intestinal tissue of SAO-shock rats. Moreover, LY-189444, a closely related compound having no LTB4 antagonist activity, did not protect rats in SAO shock, whereas a lipoxygenase inhibitor confirmed protection in SAO shock. These results suggest that LTB4 plays a pivotal role in endothelial dysfunction occurring in SAO-shock rats by chemoattraction and activation of neutrophils on the surface of vascular endothelial cells. Moreover, LY-255283 but not LY-189444 inhibited the adherence of rat neutrophils to isolated SMA endothelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ethanol consumption on bioactivation and hepatotoxicity of N-nitrosodimethylamine in rats

To study the effects of ethanol on the hepatotoxicity of N-nitrosodimethylamine (NDMA), 5 mg NDMA/kg body weight was injected intraperitoneally 3 times a week for 6 weeks into rats pair-fed liquid diets containing 36% of energy either as ethanol or as additional carbohydrates. Another group of rats was pair-fed with the same diets but injected with saline instead of NDMA. Co-administration of ethanol and NDMA produced much higher elevations of serum alanine and aspartate aminotransferase and glutamic dehydrogenase activities than the administration of either agent alone. The combined treatment also slightly increased focal necrosis, whereas other liver lesions (steatosis and fibrosis) and the functional impairment of mitochondrial respiration were not affected significantly. Microsomal low Km NDMA demethylation, as well as NDMA denitrosation, were inhibited markedly by incubation with an antibody against P450IIE1, suggesting the involvement of this alcohol-inducible P450 in both NDMA bioactivation reactions. The addition of ethanol inhibited P450-dependent demethylation and denitrosation of NDMA in liver microsomes, whereas both activities were enhanced markedly by chronic ethanol administration. At ethanol concentrations similar to those prevailing in the blood of alcohol-fed animals at the time of NDMA administration, hepatic microsomal demethylation and denitrosation remained significantly higher in ethanol-fed rats given NDMA than in controls. Our results suggest that bioactivation plays a critical role in the hepatotoxicity of NDMA and its aggravation by chronic alcohol consumption.

Beneficial effects of transforming growth factor-beta and tissue plasminogen activator in splanchnic artery occlusion and reperfusion in cats

We studied the effects of transforming growth factor-beta (TGF-beta), tissue plasminogen activator (tPA), and their combination in cats subjected to splanchnic artery occlusion (SAO) with reperfusion. Untreated anesthetized cats subjected to total occlusion of the celiac, superior, and inferior mesenteric arteries for 120 min, followed by reperfusion, uniformly died within 120 min after reperfusion. The mean survival time was 75 +/- 8 min. Plasma amino-nitrogen concentrations and cathepsin D and myocardial depressant factor (MDF) activities were markedly elevated following reperfusion. Superior mesenteric artery (SMA) rings isolated from cats subjected to SAO with reperfusion exhibited a significant loss of vasorelaxation to the endothelium-dependent dilators acetylcholine and A-23187. Administration of tPA (1 mg/kg) intravenously just before reperfusion did not prolong survival time (81 +/- 10 min) nor did it influence any biochemical or cardiovascular responses following reperfusion or ameliorate the depressed endothelium-dependent relaxation of SMA rings. In contrast, TGF-beta (50 micrograms/cat) ameliorated the SAO postreperfusion state in terms of survival rate and plasma MDF activity, and protected against depressed endothelium-dependent relaxation of SMA rings. TGF-beta alone slightly increased the survival time to 102 +/- 11 min. However, combined treatment with tPA (1 mg/kg) and TGF-beta (50 micrograms/cat) preserved endothelium-dependent relaxation and prevented increases in plasma amino-nitrogen more prominently than TGF-beta given alone and significantly increased the survival time to 118 +/- 3 min (p less than 0.01). These results indicate that TGF-beta exerts beneficial effects in SAO followed by reperfusion in cats, and tPA has an augmenting action on some of the beneficial effects of TGF-beta. These findings suggest that TGF-beta alone or in combination with tPA may be potentially useful therapeutic regimens in splanchnic ischemia shock by preserving splanchnic parenchymal and endothelial cells.

Neutrophil-mediated vasoconstriction and endothelial dysfunction in low-flow perfusion-reperfused cat coronary artery

We investigated the interaction between activated cat polymorphonuclear neutrophils (PMNs) and coronary vascular endothelial cells in vitro. It was shown that 1) 90 minutes of low-flow perfusion without reperfusion had no deleterious effects on endothelium-dependent vasodilation, whereas 90 minutes of low-flow perfusion and 20 minutes of reperfusion with a blood cell-free solution induced a 20-25% endothelial dysfunction; 2) activated PMNs produced endothelium-dependent vasoconstriction in coronary artery rings isolated from cat hearts undergoing 90 minutes of low-flow perfusion and 20 minutes of reperfusion with a blood cell-free Krebs-Henseleit solution; 3) addition of the superoxide free radical scavenger, superoxide dismutase (150 micrograms/ml), or an antibody directed against CD18 of PMN adherence glycoprotein complex (MAbR15.7, 20 micrograms/ml) attenuated PMN-induced vasoconstriction significantly, but addition of a hydroxyl radical scavenger [N-(2-mercaptopropionyl)-glycine, 150 micrograms/ml], a cyclooxygenase inhibitor, or a lipoxygenase inhibitor had no protective effect; 4) exposure of rings to a superoxide radical-generating system (i.e., xanthine and xanthine oxidase) produced significant vasoconstriction that was similar to that observed with activated PMNs and was inhibited by superoxide dismutase; and 5) activated PMNs produced a marked coronary endothelial dysfunction characterized by a decreased response to the endothelium-dependent vasodilators acetylcholine and A23187. Addition of either superoxide dismutase or MAbR15.7 protected against endothelial dysfunction. These results indicate that activated PMNs produce significant vasoconstriction and endothelial dysfunction in coronary arteries isolated from low-flow perfusion-reperfused hearts. These effects appear to be mediated primarily by superoxide radicals generated by activated PMNs that either inactivate or inhibit the synthesis and release of endothelium-derived relaxing factor. We conclude that activated PMNs are able to induce endothelial dysfunction by releasing free radicals and possibly other substances.

Mechanisms of inhibition of nitric oxide production in a murine model of splanchnic artery occlusion shock

Nitric oxide has been thought to be a major endothelium-derived relaxing factor which is synthesized from L-arginine and can be selectively inhibited by L-NG-monomethyl arginine. On the other hand, another endothelium-derived vasorelaxant, defined as endothelium-derived hyperpolarizing factor, has been reported. We compared their role in regulating the splanchnic vascular tone in splanchnic artery occlusion shock in the rat. Administration of L-NG-monomethyl arginine (100 mg/kg) given 5 min prior to reperfusion of splanchnic arteries which were occluded for 45 min, produced a significant increase in mean arterial blood pressure. However, the indices of the severity of shock status, including survival time, survival rate and increases in hematocrit, plasma cathepsin D and myocardial depressant factor activity following splanchnic artery occlusion shock were not exacerbated by administration of L-NG-monomethyl arginine. Addition of L-NG-monomethyl arginine (1 mg/ml) induced a small but significant increase in basal vascular tone of superior mesenteric artery rings, but it failed to totally block acetylcholine-induced vasorelaxation (48 +/- 4% relaxation). Although there were no significant changes in basal vascular tone after administration of glibenclamide (30 micrograms/ml), acetylcholine-induced vasorelaxation was significantly attenuated (58 +/- 4% relaxation). When L-NG-monomethyl arginine and glibenclamide were added together, acetylcholine-induced vasorelaxation was almost totally abolished (18 +/- 2% relaxation). Our results indicate that rat splanchnic artery endothelial cells may produce both endothelium-derived relaxing and hyperpolarizing factor. Endothelium-derived relaxing factor plays an important role in the regulation of basal vascular tone of the splanchnic circulation, while endothelium-derived hyperpolarizing factor may be important in modulating the mesenteric blood flow following splanchnic artery occlusion shock.

Cardioprotective and endothelial protective effects of [Ala-IL8]77 in a rabbit model of myocardial ischaemia and reperfusion

1 We studied the effects of a form of interleukin-8 (i.e., [Ala-IL8]77) on endothelial dysfunction and myocardial injury in rabbits. Pentobarbitone-anaesthetized rabbits were subjected to 1.5 h occlusion of the marginal coronary artery and 3.5 h reperfusion. [Ala-IL8]77 (50 micrograms or its vehicle) was given i.v. as a bolus 10 min prior to reperfusion. [Ala-IL8]77 was also studied in isolated perfused hearts of rabbits. 2 Myocardial ischaemia plus reperfusion in untreated rabbits produced severe endothelial dysfunction and myocardial injury, including marked myocardial necrosis, elevated cardiac myeloperoxidase (MPO) activity in ischaemic cardiac tissue, and loss of response of marginal coronary rings to the endothelium-dependent vasodilators, acetylcholine (ACh) and A23187. 3 Administration of [Ala-IL8]77 10 min prior to reperfusion resulted in significant protective effects in post-ischaemic reperfusion. Compared with untreated rabbits, [Ala-IL8]77 caused a reduced necrotic zone (P less than 0.01), lower MPO activity in the necrotic zone (P less than 0.05), and significantly preserved vasorelaxant responses of marginal coronary artery rings to endothelium-dependent vasodilators, ACh (P less than 0.001) and A23187 (P less than 0.001). 4 These results indicate that myocardial ischaemia and reperfusion result in a severe endothelial dysfunction and myocardial injury which involved the interaction of neutrophils and endothelial cells. However, [Ala-IL8]77 did not appear to exert a direct endothelial protective effect in the absence of neutrophils in rabbit isolated perfused hearts. 5 Inhibition of neutrophil accumulation in the myocardium, perhaps by prevention of endothelial dysfunction resulting from [Ala-IL8]77, leads to significant protective effects in ischaemia and reperfusion in rabbits.

Role of endothelial dysfunction in the pathogenesis of reperfusion injury after myocardial ischemia

Endothelial dysfunction occurs after myocardial ischemia and reperfusion characterized by a marked reduction in endothelium-dependent relaxation (EDR) due to reduced release or action of endothelium-derived relaxing factor (EDRF). This reduced EDR occurs in coronary rings isolated from cats 2.5 min after reperfusion and in isolated perfused cat hearts 2.5 min after reperfusion. No decrease in EDR occurs before reperfusion in either preparation, suggesting that this impairment in EDR occurs during reperfusion. The decrease in EDR occurs soon after the generation of superoxide radicals by the reperfused coronary endothelium. Accumulation of neutrophils and myocardial cell injury does not occur until 3-4.5 h after reperfusion. Thus, endothelial generation of superoxide radicals acts as a trigger mechanism for endothelial dysfunction which is then amplified by neutrophil adherence and diapedesis into the ischemic region enhancing post-reperfusion ischemic injury. Agents that preserve endothelial function or inhibit neutrophil activation (e.g., superoxide dismutase, prostacyclin analogs, TGF-beta, antibodies to adhesive proteins) can protect against endothelial dysfunction and myocardial injury, if administered before reperfusion.

Protection of endothelial damage and systemic shock by benidipine, a calcium antagonist, in rats subjected to splanchnic ischemia and reperfusion

Splanchnic artery occlusion (SAO) with subsequent reperfusion elicits a severe form of circulatory shock. To study the possible involvement of Ca2+ overload in this shock state, we have examined the effects of benidipine, a novel long-acting calcium antagonist, in a rat model of SAO shock, focusing on endothelial damage. Pentobarbital-anesthetized rats were subjected to 90-min occlusion of both the celiac and superior mesenteric arteries, followed by reperfusion. Rats given only the vehicle for benidipine developed hypotension following reperfusion, and only 7 of 16 rats (44%) survived 2 hr of reperfusion. In isolated superior mesenteric rings from SAO-shock rats, the EDRF-dependent dilator response to acetylcholine (ACh) (100 mM) was severely depressed (9% vs. 97% in control artery rings, P less than 0.001), whereas the EDRF-independent dilator response to acidified NaNO2 (100 microM) was unchanged. By contrast, 90% (9 of 10, P less than 0.05) rats treated with benidipine 45 min postocclusion (3 micrograms/kg, i.v.) survived 2 hr, and the dilator response to ACh was markedly improved (49% of initial, P less than 0.001). SAO-shock rats treated with benidipine also exhibited significantly attenuated accumulation of free amino-nitrogenous compounds (5.5 vs. 7.9 U/ml, P less than 0.05) and myocardial depressant factor (34 vs. 62 U/ml, P less than 0.001). These results suggest that endothelial damage plays a role in the pathogenesis of shock following bowel ischemia and reperfusion and that Ca(2+)-entry blockade improves endothelial function, which is involved in the amelioration of the shock state.

Mechanism of the protective action of Bay-u-3405, a new specific thromboxane receptor antagonist, in arachidonate-induced sudden death

Injection of sodium arachidonate (NaAr) intravenously at a dose of 2 mg/kg is uniformly lethal in rabbits within 3 min. This sudden death is characterized by a precipitous drop in mean blood pressure within 2 min after injection of NaAr, a marked decrease in the circulating platelet count, a significant increase in intratracheal pressure and in plasma thromboxane A2 (TxA2) concentration as measured by radioimmunoassay of its stable breakdown product, TxB2. Pretreatment with Bay-u-3405, a new specific thromboxane receptor antagonist, at a dose of 1 or 10 mg/kg dramatically protected rabbits against sudden death induced by injection of NaAr. All of the rabbits treated with either of these two doses of Bay-u-3405 survived, and their thrombocytopenia, elevated plasma TxB2 concentration and bronchoconstriction were significantly attenuated. However, administration of 0.1 mg/kg Bay-u-3405 exerted no protective effect in this lethal model. Bay-u-3405 was shown to be a potent and specific inhibitor of thromboxane-mimetic induced platelet aggregation in vitro. Our data clearly show that Bay-u-3405 is a very effective protective agent against NaAr-induced sudden death in rabbits, blocking all of the known deleterious effects of TxA2.

Daltroban, a thromboxane receptor antagonist, protects the myocardium against reperfusion injury following myocardial ischemia without protecting the coronary endothelium

The effects of daltroban, a specific thromboxane receptor antagonist, were investigated in a model of myocardial ischemia consisting of 1.5 h of coronary artery occlusion followed by reperfusion for 4.5 h in anesthetized cats. Daltroban (1 mg/kg) was infused as a bolus 10 min prior to reperfusion of the left anterior descending (LAD) coronary artery. Daltroban infusion resulted in a significantly lower necrotic area expressed as a percentage of the myocardial area-at-risk compared to the MI + vehicle group. However, daltroban failed to retard increases in myeloperoxidase activity in the ischemic myocardium, indicating no reduction in neutrophil accumulation. Moreover, left anterior descending coronary artery ring preparations isolated from daltroban treated MI cats exhibited endothelial dysfunction following ischemia reperfusion. Thus, daltroban significantly protected the myocardium from reperfusion injury without protecting the coronary endothelium or retarding neutrophil accumulation.

Acetaldehyde-collagen adducts in CCl4-induced liver injury in rats

Circulating AC levels as well as antibodies against AC-protein adducts are increased in non-alcoholic liver injury. To identify the adducts, we used rats with CCl4-induced cirrhosis. Liver subcellular fractions were analyzed by immunochemical staining of protein slot blots and of electrophoretically separated proteins, transferred to nitrocellulose, using AC-protein adduct-specific antibodies. One reactive protein of about 200 kD was detected in the liver soluble fraction and in the cytosol of isolated hepatocytes and, to a lesser extent in the liver microsomes of CCl4-treated rats; in control animals, this reactivity was much weaker. The immunopositive AC adduct co-migrated with the beta 1,2 dimer of rat collagen type I; it was sensitive to digestion by a highly purified collagenase and also reacted with anti-rat collagen type I-specific IgG. In addition, comparison of peptides of the CNBr-digested, immunoprecipitated AC adduct with those of rat collagen type I revealed a high degree of similarity. Thus, AC adduct formation occurs in liver injury of non-alcoholic origin, and a target protein appears to be related to collagen type I, most likely the procollagen precursor.

High levels of acetaldehyde in nonalcoholic liver injury after threonine or ethanol administration

Acetaldehyde, a product of ethanol oxidation which forms adducts with proteins, has been incriminated in the pathogenesis of alcoholic liver injury. High serum antibody titers against acetaldehyde-protein adducts have been found not only in alcoholics but also in patients with nonalcoholic liver disease, suggesting a contribution of acetaldehyde derived from sources other than exogenous ethanol. To investigate the effect of liver injury on the removal and the production of acetaldehyde, we produced fibrosis and cirrhosis (by chronic administration of carbon tetrachloride) and fatty liver (with very small doses of dimethylnitrosamine) in rats. Endogenous blood acetaldehyde levels increased by 38% in rats with severe liver injury (p less than 0.005), but not significantly in rats with fatty liver. However, an i.v. load of threonine (a physiological source of acetaldehyde), in amounts equivalent to the daily intake of this amino acid, increased blood and hepatic acetaldehyde levels in the rats with both types of liver injury more than in controls. Threonine dehydrogenase and dehydratase activities, involved in the major pathways for threonine degradation in mitochondria and cytosol, respectively, were markedly decreased in rats with liver injury with a resulting increase in hepatic threonine concentration. Moreover, the threonine aldolase activity, which splits threonine into glycine and acetaldehyde, remained unaffected or even slightly increased. Liver injury was also associated with impaired mitochondrial functions, including a 10 to 23% decrease in acetaldehyde oxidation (depending upon the severity of the lesions). As a consequence, administration of ethanol (an exogenous source of acetaldehyde) resulted in striking elevations in the levels of acetaldehyde in carbon tetrachloride-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

[Changes in platelet aggregation and coronary collateral circulation during the early phase of myocardial ischemia in dogs]

Experiments were performed on 18 anesthetized open-chest dogs to observe the changes in platelet aggregation and coronary collateral circulation during the early phase of acute myocardial ischemia. An increase in platelet aggregation rates (PAgR) and a decrease in platelet counts (PC) were found in the blood collected from the ischemic myocardium after coronary occlusion. PAgR was increased by 58.7 +/- 5.6% and PC was reduced by 39.5 +/- 23.6% at 50 min after occlusion (P less than 0.01). Under the condition of controlling aortic blood pressure, collateral coronary vascular capacity (CVC) was not changed (P greater than 0.05), but the effective collateral coronary flow to the ischemic zone, calculated by Wyatt et al's equation, was significantly reduced by 23.5 +/- 9.7% at 50 min after occlusion (P less than 0.05). There was a negative correlation between the changes in PAgR and the effective collateral coronary flow ( r = -0.857, P less than 0.01), and between the collateral indices and infarct size (r = -0.847, P less than 0.01). Abnormal changes in parameters of platelet and coronary collateral circulation after myocardial ischemia were nearly abolished by intravenous injection of aspirin before coronary occlusion. The results suggest that the deleterious changes of platelet aggregation during the early phase of the acute myocardial ischemia may decrease the effective collateral coronary flow significantly and thereby enlarge the infarct size.

[Effects of splenectomy on changes in hemorrheologic parameters following coronary occlusion in dogs]

Effects of splenectomy on changes of hemorrheologic parameters in the early stage of myocardial ischemia were observed in dogs. The results showed that splenectomy alleviated the increase in hematocrit and high shear viscosity of whole blood (r = 230 s-1) during 120 min of myocardial ischemia induced by coronary occlusion. Splenectomy reduced the increase in low shear viscosity of whole blood (r = 5.75 s-1) at 40 min and 80 min post-occlusion, but did not affect it at 120 min post-occlusion. Splenectomy had no effect on changes in blood viscosity fibrinogen concentration and plasma viscosity following coronary occlusion.