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.