Limb ischemia-induced increase in permeability is mediated by leukocytes and leukotrienes

This study tests the role of white blood cells (WBC) and leukotrienes in mediating the increased microvascular permeability following ischemia and reperfusion. Anesthetized dogs (n = 23) underwent 2 hours of hind limb ischemia induced by tourniquet inflation to 300 mmHg. In untreated animals (n = 7), tourniquet release led after 5 minutes to a rise in plasma thromboxane (Tx) B2 levels from 360 to 1702 pg/ml (p less than 0.05); after 2 hours, lymph TxB2 concentration had risen from 412 to 1598 pg/ml (p less than 0.05). There were decreases in circulating WBC from 11,766 to 6550/mm3 and platelets from 230 to 155 x 10(3)/mm3. During reperfusion, popliteal lymph flow (QL) increased from 0.07 to 0.24 ml/hour (p less than 0.05), while the lymph/plasma (L/P) protein ratio was unchanged from 0.39, changes consistent with increased microvascular permeability. WBC depletion (n = 7) to 302/mm3 by hydroxyurea or nitrogen mustard attentuated (p less than 0.05) the reperfusion induced rise in plasma TxB2 from 91 to 248 pg/ml and prevented the increase in lymph TxB2 concentration. Within 5 minutes of tourniquet release WBC counts further decreased to 191/mm3 (p less than 0.05) and platelets declined from 175 to 93 x 10(3)/mm3 (p less than 0.05). QL increased from 0.07 to 0.12 ml/hour (p less than 0.05), lower than untreated animals (p less than 0.05), and the L/P protein ratio declined from 0.49 to 0.37 (p less than 0.05), dilutional changes consistent with increased filtration pressure but not permeability to protein. Pretreatment with the lipoxygenase inhibitor diethylcarbamazine (DEC) (n = 8) prevented the reperfusion-induced increase in plasma and lymph TxB2 levels (p less than 0.05) and the fall in WBC counts (p less than 0.05), while platelet counts declined from 381 to 210 x 10(3)/mm3 (p less than 0.05). QL rose from 0.09 to 0.23 ml/hour (p less than 0.05) during reperfusion, and the L/P protein ratio of 0.3 remained unchanged, a value lower than in untreated dogs (p less than 0.05). In two animals of each group, vascular recruitment was induced by tourniquet inflation to 50 mmHg. This led to a high QL of 0.25 ml/hour and a low L/P ratio of 0.18. In untreated animals during reperfusion, QL further increased to 1.3 ml/hour, and L/P ratio rose to 0.44, documenting increased vascular permeability. In contrast, reperfusion in leukopenic or diethylcarbamazine (DEC)-treated dogs with vascular recruitment, was not associated with increases in QL or the L/P protein ratio.(ABSTRACT TRUNCATED AT 400 WORDS)

Reperfusion injury of postischemic tissues

Reperfusion injury, occurring when blood circulation is restored to previously ischemic tissues, is now demonstrable as a pathophysiologic entity distinct from the primary ischemic injury that develops during ischemia per se. The primary pathogens that cause reperfusion injury are thought to be partially reduced oxygen species, including superoxide radicals, hydrogen peroxide, and hydroxyl radicals, which initiate lipid peroxidation and other deleterious oxidation reactions during the reperfusion period. Antioxidant drugs, given at the end of ischemia or at the very onset of reperfusion, can improve the postischemic function of isolated organs and the survival of intact animals subject to a cycle of circulatory arrest and reperfusion, suggesting that reperfusion injury is both a real and a preventable pathophysiologic entity.

Copper intake affects rat heart performance during ischemia-reperfusion: possible relation to altered lipid and fatty acid metabolism

Hearts from rats fed low copper (1.3 mg copper/kg diet) or a copper-supplemented diet (243 mg copper/kg diet) were perfused for 90 min according to the Langendorff method. The perfusion protocol included 30 min normoxia, 30 min ischemia and 30 min reperfusion. After 90 min perfusion, hearts from the low copper group had gained more weight, had lower coronary perfusion pressure, developed less force of contraction and secreted less 6-keto PGF1 alpha into the perfusate than hearts from the copper-supplemented group. After perfusion, the major lipid change in the hearts from both groups was a 85-90% decrease in total triacylglycerol. In both groups, stearic acid and arachidonic acid (mg%) were increased in the triacylglycerol fraction after heart perfusion. The quantitative (mg/g) decrease in the triacylglycerol content of stearic acid and arachidonic acid was significantly less in the copper-supplemented group. After perfusion, dihomo-gamma-linolenic acid (mg/g) was lower in heart phospholipids from the low copper group. Dihomo-gamma-linolenic/arachidonic acid (microgram/mg) was significantly decreased after perfusion only in the hearts from the low copper group. Lipid and fatty acid changes in the hearts of the rats fed low dietary copper may contribute to abnormal heart function in this group.

The effects of L655,240, a selective thromboxane and prostaglandin endoperoxide antagonist, on ischemia- and reperfusion-induced cardiac arrhythmias

The purpose of this investigation was to provide a detailed analysis of the effects of the thromboxane antagonist L655,240 (0.3 mg/kg i.v.) on early ischemia- and reperfusion-induced arrhythmias in a canine model of coronary artery occlusion. In a dose that abolished the pulmonary response to U46619, L655,240 attenuated markedly the severity of those arrhythmias that resulted from reperfusion of the myocardium; survival from the combined occlusion-reperfusion insult was increased from 10% in control animals to 70% in dogs administered L655,240. Drug intervention did not significantly alter the total number of arrhythmias during the period of ischemia, but a detailed analysis of the different types of arrhythmia that occurred during this period showed that L655,240 significantly reduced those arrhythmias in phase 1a (0-10 min of occlusion) without affecting the later phase 1b arrhythmias. This was particularly shown in the marked reduction in the number of salvos (couplets and triplets) during this period. Neither those arrhythmias occurring later in the ischaemia period (phase 1b) nor the total number of single ectopics and salvos or the incidence and duration of ventricular tachycardia was modified by L655,240. These results reveal that thromboxane antagonism protects especially against reperfusion-induced ventricular fibrillation and against early (phase 1a) ischemia-induced arrhythmias, possibly implicating a role for thromboxane in the genesis of these cardiac rhythm disturbances.

Cardiac renin-angiotensin system. Molecular and functional aspects

Current data support the existence of an endogenous renin-angiotensin system in the heart. Vascular angiotensin may contribute to the regulation of coronary vascular tone. Enhanced local angiotensin production in areas of vascular injury or inflammation may result in increased vasoconstriction or vasospasm. Cardiac angiotensin may adversely influence myocardial metabolism and provoke ventricular arrhythmia during ischemia and reperfusion-induced myocardial injury. Local angiotensin may stimulate cardiac contractility. In addition, angiotensin may influence cardiac myocyte growth and may contribute to the development of cardiac hypertrophy in hypertension. Recent data show that the pharmacologic inhibition of cardiac angiotensin converting enzyme may have important therapeutic consequences for the ischemic, hypertrophic, or failing heart.

Anti-ischaemic activity of various calmodulin antagonists

The anti-ischaemic activity of the calmodulin antagonists trifluperazine, felodipine, W-7 and calmidazolium has been investigated in electrically paced guinea-pig hearts, perfused according to Langendorff, which were subjected to 60 min of global ischaemia followed by 30 min of reperfusion. At concentrations that induced a comparable reduction in cardiac contractile force, trifluperazine, felodipine and to a lesser extent W-7, were associated with improvement of post-ischaemic functional (LVP and coronary flow) and biochemical parameters (CrP and ATP). Furthermore, felodipine and trifluperazine delayed the onset and suppressed the maximum tension of the ischaemic contracture was observed. In contrast, calmidazolium had no anti-ischaemic effects. This lack of anti-ischaemic activity of the most potent calmodulin antagonist calmidazolium, as well as the significant calcium entry blocking activity of both trifluperazine and felodipine suggest that additional factors besides calmodulin antagonism may contribute to the anti-ischaemic activity of these compounds.

Mechanisms of oxidant-mediated microvascular injury following reperfusion of the ischemic intestine

Based on work from our laboratory and studies by others, we propose the following hypothesis to explain the interaction among xanthine oxidase, PMNs, and tissue injury in the postischemic small intestine (Figure 2). During the ischemic period, ATP is catabolized to yield hypoxanthine. The hypoxic stress also triggers the conversion of NAD-reducing xanthine dehydrogenase to the oxygen radical-producing xanthine oxidase via a protease. When the intestine is reperfused, molecular oxygen is reintroduced into the tissue where it reacts with hypoxanthine and xanthine oxidase to produce a burst of superoxide anion and hydrogen peroxide. In the presence of ferric iron, superoxide anion and hydrogen peroxide react via the Haber-Weiss reaction to form hydroxyl radicals. This highly reactive and cytoxic free radical then initiates lipid peroxidation of cell membrane components and the subsequent release of substances that activate, attract, and promote the adherence of PMN to microvascular endothelium. The adherent PMN then causes further endothelial cell injury via the release of superoxide and various proteases.

Potential of methylene blue to block oxygen radical generation in reperfusion injury

Methylene blue interacts with xanthine oxidase at the iron-sulfide site in the electron pathway (Scheme I) that is known to serve as an electron-sink connecting the reductive and oxidative sites in both the oxidase and dehydrogenase forms. Thus, shunting of electrons to methylene blue at this site effectively diverts their flow away from the FAD site where molecular oxygen is converted to superoxide radicals. Since the electron affinity constants of xanthine oxidase for electron acceptors are FAD greater than iron/sulfide greater than molybdenum, methylene blue falls between the FAD and iron-sulfide site. Thus, methylene blue effectively inhibits superoxide and hydroxyl radical production while accelerating the conversion of xanthine to uric acid. As methylene blue is already approved for medicinal use in humans and is relatively nontoxic, the drug may have a role in reducing tissue injury associated with reperfusion. We are currently investigating this possibility in animal models.