[Oxygen free radicals and inflammatory diseases of intestines]

Free oxygen radicals (F.O.R.) belong to a very aggressive chemical species derived from molecular oxygen. Their role in inflammation is well established and Polymorphonuclear neutrophils (PMNS) make use of them as antibacterial weapons. Their role has been experimentally demonstrated in numerous ischemia-reperfusion models. Free radical scavengers such as the superoxide dismutase, allopurinol or desferrioxamine can prevent the occurrence of lesions. The essential role of PMNS in these models is demonstrated by the fact that previous depletion of the animal in PMNS also prevents such lesions. Histologically, in these ischemia-reperfusion models, PMNS infiltration may be quantified by assay of myeloperoxidase. In experimental models of inflammatory colitis (acetic acid, bacterial polysaccharides) intestinal wall infiltration by PMNS is a fundamental phenomenon and is also a characteristic of Crohn's disease and exacerbations of Ulcerative Colitis. Thus, it is probable in both disorders that F.O.R. play an important role since steroids inhibit their secretion by PMNS and 5-aminosalicylic acid has been shown to be a F.O.R. scavenger.

Do leukocytes have a role in the cerebral no-reflow phenomenon?

The possible role of leukocytes in the cerebral microcirculation following ischaemia was assessed in the gerbil. The no-reflow phenomenon seen after 30 minutes of severe bilateral hemispheric ischaemia during hypotensive reperfusion was compared in control animals and in a group made leukopenic by pretreatment with cyclophosphamide. Neither the incidence nor the severity of the no-reflow phenomenon differed between the two groups. The evidence from this study casts doubt on the hypothesis that leukocyte plugging plays a major role in the cerebral microcirculation's response to ischaemia.

The beneficial effect of intermediate normothermic perfusion during cold storage of ischemically injured kidneys. A study of renal nucleotide homeostasis during hypothermia in the dog

The effect of simple cold storage on ice with or without preceding warm ischemic injury on the energy metabolism and posttransplant viability of canine kidneys was examined in the present study. In addition, we investigated the possible beneficial effect of an intermediate normothermic perfusion half-way through the storage period on the preservation of ischemically injured kidneys. Thirty mongrel dogs were allocated to 5 experimental groups. In groups I and II kidneys were simply stored on ice for 24 and 48 hr, respectively. In groups III and IV kidneys were additionally subjected to 30 min warm ischemia before storage. In group 5 kidneys were treated as in group IV, but halfway through the storage period an intermediate normothermic ex-vivo perfusion was performed. The effect of these procedures on renal viability was tested by autologous reimplantation of the kidneys. During implantation the contralateral kidney was immediately removed. In group I all animals survived, whereas in group IV none of the animals survived. In groups II, III, and V, 2 of 6, 1 of 6, and 3 of 6 animals survived, respectively. The relationship, if any, between poststorage renal viability and the tissue levels of adenine nucleotides, guanine nucleotides, IMP, and purine degradation products was assessed by measuring the content of these metabolites in tissue specimen of the renal cortex, on which biopsies were done at various intervals during the experimental procedures. After an initial drop of about 30% in the content of adenine and guanine nucleotides and an increase in IMP, these values remained constant during 48 hr of cold storage. In contrast to kidneys stored for 24 hr, reimplantation of kidneys stored for 48 hr resulted in a significant decrease of adenine nucleotides following 60 min of in vivo reperfusion. Warm ischemia for 30 min prior to cold storage lead to lower initial nucleotide levels at the start of the storage period. During the first 24 hr nucleotide levels did not change, but a further decrease was observed during the following 24 hr of storage. Reimplantation after 24 hr of storage resulted in an additional decrease in the content of nucleotides. This poststorage decrease was absent after 48 hr of cold storage. Intermediate normothermic perfusion halfway through the storage for 48 hr significantly prevented the drop in the nucleotide content observed during the last 24 hr of storage in the corresponding control group. This nucleotide-sparing effect did not increase the level of nucleotides at the end of 60 min of reperfusion following reimplantation.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrophysiological and antiarrhythmic effects of UK 52,046-27 during ischaemia and reperfusion in the guinea-pig heart

1. We studied the antiarrhythmic and electrophysiological effects of UK 52,046-27 (10(-8) M and 5 x 10(-8) M), a highly selective alpha 1-adrenoceptor antagonist, during global ischaemia (flow reduced to 10% of control for 30 min) and reperfusion, in isolated, buffer-perfused hearts of guinea-pigs. 2. The compound had few electrophysiological effects during normal perfusion, although action potential amplitude and Vmax were reduced with 10(-8) M (by 9% and 22%) and refractory period was increased with 5 x 10(-8) M (by 13%) compared to control hearts. 3. Perfusion with 5 x 10(-8) M UK 52,046-27 reduced the incidence of ventricular tachycardia during ischaemia from 67% to 25%, and during reperfusion reduced the incidence of ventricular tachycardia (from 83% to 17%) and ventricular fibrillation (from 67% to 8%). 4. The compound prolonged significantly action potential duration and refractory period during ischaemia and reperfusion. Vmax was reduced to a greater extent during reperfusion in the treated hearts, while greater increases in QRS width and stimulation threshold occurred during ischaemia in the treated group. 5. These results confirm that blockade of the alpha 1-adrenoceptor subpopulation during myocardial ischaemia and reperfusion decreases the incidence of arrhythmias and alters cellular electrophysiology during ischaemia and reperfusion.

Gastric mucosal perfusion and injury: variation in the relationship over time

Acute erosions of the gastric mucosa occur in a variety of clinical settings characterized by a mismatch between mucosal blood supply and demand. Using a canine model incorporating the clinically important insults, we examined the relationship between the gastric mucosal injury measured by planimetry and the animal's regional gastric perfusion measured before, during, and after hemorrhagic shock. The proximal gastric mucosa developed lesions which were inversely related to the amount of gastric flow through 2 hours of shock. In later shock and after reperfusion the relationship reversed, coinciding with the appearance of visible ulcerations. This work demonstrates that early in shock gastric blood flow is inversely related to mucosal injury, but late in shock and after reperfusion increased blood flow is associated with increased mucosal damage.

Reperfusion pulmonary edema

Reperfusion following lower-torso ischemia in humans leads to respiratory failure manifest by pulmonary hypertension, hypoxemia, and noncardiogenic pulmonary edema. The mechanism of injury has been studied in the sheep lung lymph preparation, where it has been demonstrated that the reperfusion resulting in pulmonary edema is due to an increase in microvascular permeability of the lung to protein. This respiratory failure caused by reperfusion appears to be an inflammatory reaction associated with intravascular release of the chemoattractants leukotriene B4 and thromboxane. Histological studies of the lung in experimental animals revealed significant accumulation of neutrophils but not platelets in alveolar capillaries. We conclude that thromboxane generated and released from the ischemic tissue is responsible for the transient pulmonary hypertension. Second, it is likely that the chemoattractants are responsible for leukosequestration, and, third, neutrophils, oxygen-derived free radicals, and thromboxane moderate the altered lung permeability.

Acceleration of recovery of mitochondrial function after coronary reperfusion by various coronary dilating drugs in canine hearts

This study was designed to evaluate whether or not increase in coronary blood flow after reperfusion accelerates the recovery of ischemia-induced mitochondrial damage. Using anesthetized dogs, the left anterior descending coronary artery was occluded for 30 min, followed by 20 min of reperfusion. Five minutes after reperfusion, either physiological saline (n = 9), 0.5 mg/kg of dilazep (n = 7), 0.2 mg/kg of diltiazem (n = 7), or 0.5 mg/kg of nicorandil (n = 8) were administered intravenously. Arterial blood pressure, heart rate, and coronary blood flow were measured throughout the experiment. Twenty minutes after reperfusion, heart mitochondria from normal and reperfused areas were prepared, and mitochondrial function was measured. Significant increase in coronary flow was observed during reperfusion in all drug-treated groups; however, no significant increase was observed in the control group 10 min after reperfusion. Significant hemodynamic changes were not observed in all groups. Mitochondrial function from reperfused areas was recovered significantly in all drug-treated groups, though in the control group mitochondrial dysfunction persisted. Coronary dilative mechanisms of drugs used here differ; however, a similar effect was demonstrated, i.e., administration of a coronary dilator accelerates the recovery of mitochondria after reperfusion. Therefore, it is concluded that coronary flow after reperfusion might be a primary factor in the recovery of ischemia-induced mitochondrial damage.

Improvement of ischemia-reperfusion-induced myocardial dysfunction by modulating calcium-overload using a novel, specific calmodulin antagonist, CGS 9343B

The present paper explores the mechanism of calcium-overloaded cardiac cell exocytosis during reperfusion of ischemic myocardium. A novel specific inhibitor of calmodulin, CGS 9343B, was used to pretreat an ischemic heart in an effort to enhance myocardial preservation. The experimental model employed an isolated in situ pig heart subjected to 120 min of ischemic insult by reversibly occluding the left anterior descending coronary artery, the last 60 min being superimposed with global hypothermic cardioplegic arrest. This ischemic episode was followed by 60 min of revascularization. CGS 9343B enhanced post-ischemic myocardial recovery, as judged by improved regional as well as global myocardial functions, better preservation of high-energy phosphate compounds, and reduced release of creatine kinase. Since this compound blocks calmodulin without inhibiting protein kinase C, the results of this study suggest that calmodulin-dependent kinase, rather than protein kinase C, is primarily involved in expressing calcium-overloaded cell exocytosis, and a specific calmodulin antagonist such as CGS 9343B can be used to salvage an ischemic heart from reperfusion injury.

Role of PAF in ischemia-reperfusion injury in the rat stomach

Ischemia-reperfusion induced extensive gastric mucosal injury and an increase in chemiluminescence activity of neutrophils obtained from the portal vein in hemorrhagic shock rats. CV-3988, a selective antagonist of platelet activating factor (PAF), significantly reduced the gross and histologic gastric damage, and the increase in chemiluminescence activity of neutrophils. These results suggest that PAF generated on hypoxia might stimulate oxygen radical production by neutrophils, resulting in the occurrence of gastric injury in hemorrhagic shock rats.

Dimethylthiourea, but not dimethylsulfoxide, reduces canine myocardial infarct size

We studied the effect of treatment with two diffusible, low molecular weight scavengers of toxic oxygen metabolites, dimethylthiourea (DMTU) and dimethylsulfoxide (DMSO), on canine infarcts caused by 90 min of ischemia and 3 h of reperfusion. Infarct size was determined by incubating ventricular slices with triphenyl tetrazolium chloride. Areas at risk were determined by autoradiography of 99Tc microspheres injected in vivo during ischemia and were similar (p greater than 0.05) in DMTU, DMSO, and saline treated dogs. However, the ratio of infarct size to area at risk was reduced (p less than 0.05) in dogs treated 30 min before reperfusion with 500 mg/kg DMTU (31.1 +/- 4.6%, n = 9) compared with saline treated dogs (53.4 +/- 4.6% n = 9). In contrast, the ratio of infarct size to area at risk was not significantly different (p greater than 0.05) in dogs treated with 2000 mg/kg DMSO 30 min before reperfusion (43.7 +/- 4.3%) compared to saline treated dogs. The serum concentration of DMTU (4.5 mM) was one-tenth that of DMSO (48 mM) in early reperfusion. Therefore, DMTU but not DMSO protected against post-ischemic cardiac reperfusion injury.

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.