Prostacyclin protects ischemic reperfused myocardium in the dog by inhibition of neutrophil activation

Iloprost reduces leukocyte adhesion in skeletal muscle venules following ischaemia in a rat model of femorodistal bypass

Intraarterial bolus treatment with the prostacyclin analogue iloprost appears to have a prolonged beneficial effect on femorodistal bypass graft flow which extends beyond the duration of its vasodilator properties. The effect of iloprost on the microcirculation rendered ischaemic over the time course of a distal bypass operation was investigated in this study without the use of fluorescent light.

METHODS

A rat model was designed to allow prolonged direct observation of leukocyte-venular endothelial adhesion in a femorodistal bypass simulation. The extensor digitorum longus (EDL) muscle of 10 rats was subjected to two 30 minute periods of ischaemia by a non-venous occluding tourniquet and to simulate some of the changes of chronic ischaemia the adverse effect of ischaemia was accentuated by indirect electrical stimulation via the lateral popliteal nerve.

RESULTS

Intraarterial bolus treatment with iloprost significantly reduced the total numbers of leukocytes observed in EDL venules, and the numbers exhibiting evidence of adhesion by rolling or sticking to venule endothelium compared with saline controls at one hour post ischaemia. Ischaemia induced vasodilatation and reduced shear stress by a similar and significant amount in both groups.

CONCLUSION

Two periods of ischaemia and reperfusion similar to those which occur during bypass grafting resulted in changes in the distal microcirculation consistent with reperfusion injury. Intraarterial bolus treatment with iloprost prevented these leucocyte-endothelial changes. It appears iloprost may have a role in reducing leukocyte-induced reperfusion injury in femorodistal bypass surgery.

Beraprost sodium protects occlusion/reperfusion injury in the dog by inhibition of neutrophil migration

1. The effects of beraprost sodium (beraprost) on myocardial infarct size in an anesthetized open-chest canine model of regional myocardial ischemia and reperfusion were investigated. 2. Administration of beraprost (300 ng/kg/min, intravenously) to dogs 45 min after left circumflex coronary artery occlusion until 105 min after reperfusion resulted in a significant reduction in infarct size. 3. The values of control and beraprost treated infarct size expressed as a percentage of the total left ventricle were 15 +/- 3% and 4 +/- 2%, respectively. 4. Reperfusion arrhythmia, plasma creatine phosphokinase (CK) and lactate dehydrogenase (LDH) level were significantly suppressed by treatment with beraprost. 5. By histological examination, beraprost proved to reduce neutrophil migration in the ischemic myocardium after 5 h reperfusion. 6. Therefore, it is suggested that the cytoprotective effect of beraprost during myocardial ischemia and reperfusion may be the consequence of the inhibition of neutrophil migration.

Effect of duration of ischaemia on reduction of myocardial infarct size by inhibition of neutrophil accumulation using an anti-CD18 monoclonal antibody

1. Neutrophil accumulation is a characteristic feature of the inflammatory response in myocardial tissue which has undergone a period of ischaemia. The aim of this study was to examine whether inhibition of myocardial neutrophil infiltration, using an antibody to the CD18 leukocyte adhesion molecule, was effective in reducing infarct size in anaesthetized rabbits. 2. Anaesthetized rabbits underwent coronary artery occlusion (CAO) for periods of 30 or 45 min followed by reperfusion for 3 h. Animals were treated intravenously 10 min prior to reperfusion with IB4, a monoclonal antibody to CD18 (1 mg kg-1) or saline (1 ml kg-1). In one group undergoing 45 min CAO, a control antibody, OKMI (1 mg kg-1) was given. 3. Following either 30 or 45 min of CAO, administration of IB4 resulted in a < 75% inhibition in neutrophil accumulation in the area at risk myocardium (AR) compared with control animals. 4. With the 30 min occlusion period, IB4 significantly reduced myocardial infarct size, 27.2 +/- 3.2% vs 67.4 +/- 5.6% in the saline control group (n = 5 P < 0.01). In contrast, IB4 did not reduce infarct size following a 45 min period of ischaemia. 5. In the same animals administration of IB4 significantly inhibited oedema formation in skin elicited by intradermal administration of the neutrophil chemoattractant f-Met-Leu-Phe, but had no effect on coronary microvascular plasma protein leakage in the AR. 6. Our results indicate that infiltrating neutrophils exacerbate tissue injury following a relatively short, 30 min period of myocardial ischaemia in the rabbit. However, protection with IB4 was no longer seen if the period of CAO was extended to 45 min. The results in this model suggest neutrophils are not a major determinant of tissue injury following more than a very short period of ischaemia.

The effect of andrographis paniculata nees (APN) in alleviating the myocardial ischemic reperfusion injury

In experimental dogs, the effect of APN in alleviating the ischemia-reperfusion injury was prominent. Compared with the sustained ischemia group, superoxide dismutase (SOD) in the ischemic region of myocardial tissue in the ischemia-reperfusion group was significantly decreased and malondialdehyde (MDA) markedly increased: Ca2+ in myocardial cells was increased; and ultrastructural changes of myocardial tissues were severe. In the APN-pretreated ischemia-reperfusion group, on the contrary, all the above parameters showed reversely, i.e., SOD increased, MDA and intracellular Ca2+ decreased, the ultrastructure changes were less distorted.

Role of neutrophil-endothelial cell adhesion in inflammatory disorders

Polymorphonuclear leukocytes are armed with an impressive arsenal of bactericidal agents that allow these cells to play a vital role in host defense against invading pathogens. However, these same agents can produce extensive cellular damage in host tissues when leukocytes are activated during inflammatory conditions. Recognition of this fact, when coupled with the observation that leukocyte adhesion to post-capillary venules is a critical first step in the inflammatory process, has led to the development of the concept that inhibition of neutrophil-endothelial cell adhesion (NECA) may represent a novel therapeutic strategy for the prevention of leukocyte-dependent injury in inflammatory conditions. Indeed, pharmacological or immunologic inhibition of NECA reduces cellular injury, dysfunction, and necrosis induced by ischemia/reperfusion, circulatory shock and resuscitation, organ transplantation, cardiopulmonary bypass, frostbite, and thermal trauma. NECA also appears to play an important role in the pathobiology of airway inflammation and asthma, pulmonary oxygen toxicity, arthritis, bacterial meningitis, and cerebral malaria. The aim of this review is to summarize the evidence implicating NECA in the pathogenesis of these inflammatory conditions.

Polymorphonuclear leukocytes in ischemic vascular disease

Over the last decade, an extensive amount of evidence has accumulated which implicates PMN in the etiology and pathophysiology of ischemic/thrombotic diseases. It has become apparent that PMN infiltration is not, as once thought, an innocent secondary phenomenon following ischemia. Rather, PMN are active participants in the pathophysiology of infarction, exacerbating the tissue damage. Since the development of means to achieve reperfusion after thrombosis, this phenomenon has become of critical importance. Many different approaches, targeted at prevention of PMN trapping in the capillaries of the ischemic, area, have been shown to effectively reduce the final infarct size, and will likely prove valuable adjuncts to reperfusion. However, perhaps the most significant aspect of the realization that PMN play a significant role in thrombotic disease may prove to be the potential for early intervention: Elevated PMN counts are predictive of ischemic events, and there is preliminary evidence that the elevated PMN count may be also associated with increased PMN activation, suggesting that research directed at the prophylactic use of anti-PMN agents might someday prove effective in reducing the incidence of MI and stroke.

Tumor necrosis factor-alpha as a myocardial depressant substance

Most patient with sepsis and septic shock develop significant derangements of myocardial function. The presence of a circulating myocardial depressant substance (MDS) has been suggested to be the major cause of myocardial depression in sepsis and septic shock. MDS is still not fully characterized by chemical means, and there is no consensus regarding its identity. Nevertheless, high levels of MDS activity can be found in sera from patients with sepsis and septic shock. Furthermore, MDS has been shown to have a number of specific characteristics. These characteristics have also been described with tumor necrosis factor-alpha (TNF), a cytokine that is well recognized to be a primary mediator in the pathogenesis of infection, tissue injury, inflammation and shock. In this review it is suggested that TNF is an MDS, and that the cardiovascular injury and myocardial depression during sepsis and septic shock involve a final common pathway, where TNF may have an important role in this common pathway.

Decreased endothelium-dependent vascular relaxation following subtotal coronary artery occlusion in dogs

Total coronary artery occlusion followed by reperfusion leads to neutrophil accumulation in the reperfused myocardium and a reduction in endothelium-dependent coronary artery relaxation. Attenuated coronary artery relaxation in the affected regions is thought to be related to breakdown of endothelium-derived relaxing factor (EDRF) by free oxygen radicals released during reperfusion. To determine if temporary subtotal coronary artery narrowing leads to similar alteration in vascular reactivity, eight open-chest dogs were subjected to 1 h of left anterior descending (LAD) coronary artery narrowing (70% reduction in basal flow) and pacing-induced increase in heart rate (30% above baseline) followed by reperfusion for 1 h. Thereafter reactivity of ischemic-reperfused LAD and nonischemic circumflex (Cx) coronary artery rings to the thromboxane A2 analog U46,619 and EDRF-dependent vasorelaxants acetylcholine (ACh), thrombin, and adenosine diphosphate (ADP), as well as to EDRF-independent vasorelaxant nitroglycerin (NTG), was examined. Unlike in the setting of total coronary artery occlusion, reperfused myocardium or LAD did not reveal neutrophil infiltration. However, contraction in response to U46,619 was markedly (P < .001) increased in the LAD rings compared to that in the Cx rings. ACh-induced relaxation was only modestly decreased (P < .05) in the LAD coronary artery rings, but the relaxation in response to both thrombin and ADP was markedly diminished (P < .01) as compared to that in the Cx rings. Coronary artery ring relaxation in response to NTG was preserved in the LAD rings. Pretreatment of coronary artery rings with indomethacin did not alter the enhanced contraction or diminished endothelium-dependent relaxation of LAD coronary artery rings.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of anti-CD18 antibody on myocardial neutrophil accumulation and infarct size after ischemia and reperfusion in dogs

BACKGROUND

Polymorphonuclear neutrophils (PMNs) accumulate in postischemic myocardium and may cause injury to myocardium or to vessels by production of oxygen free radicals or by release of proteases and lipases. PMN accumulation is dependent on adherence to endothelium, which is mediated by a family of glycoproteins on the PMN surface, each of which has a common beta-subunit (CD18). The purpose of this study was to determine whether an antibody (IB4) against the CD18 protein could attenuate PMN accumulation and limit myocardial infarct size.

METHODS AND RESULTS

F(ab')2 fragments of a mouse monoclonal antibody to human adherence-promoting leukocyte glycoprotein (CD18) were used. Infarct size after 90 minutes of ischemia and 3 hours of reperfusion was compared in dogs with (n = 8) and without (n = 8) the anti-CD18 treatment. Myocardial PMN accumulation was assessed with 111In-labeled autologous PMNs. Anti-CD18 treatment significantly reduced the number of PMNs in the ischemic region (19,123 +/- 5,352/mg versus 5,204 +/- 927/mg in the control and treated groups, respectively; p < 0.05). In addition, the ratio of myocardial blood flow (ischemic/nonischemic wall) at 45 minutes into reperfusion was higher in the treated than in the control group (1.18 +/- 0.18 versus 0.69 +/- 0.09; p < 0.05). Nevertheless, infarct size was similar between the control and treated groups (40.5 +/- 7.4% versus 48.5 +/- 4.4% of the area at risk; p = NS). Transmural mean collateral blood flow to the ischemic myocardium was similar between the two groups, and the inverse relation between infarct size and collateral blood flow was not shifted by anti-CD18 therapy.

CONCLUSIONS

Although PMN accumulation contributed to reduced postischemic microvascular perfusion, it caused insufficient additional myocardial cell death to measurably affect infarct size in this model.

Neutrophil mediated myocardial injury

1. Activated polymorphonuclear neutrophils (PMN) were shown to exacerbate ischemic myocardial injury and their activation is modulated by complement system, platelet activating factor, arachidonic acid metabolites, adenosine and nitric oxide. 2. Mechanisms of injurious PMN effect on ischemic myocardium are related to both mechanical and biochemical processes. 3. Activated PMN aggregate and adhere to endothelium that results in capillary plugging and subsequent impairment of coronary blood flow as well as participating in the development of endothelial cell edema. 4. PMN-related biochemical damage of ischemic myocardium is a result of the release of cytotoxic free oxygen radicals and proteolytic enzymes as well as vasoconstrictor leukotriene B4 and leukotoxin.

Spontaneous superoxide generation by polymorphonuclear leukocytes isolated from patients with stable angina after physical exercise

The activation of circulating polymorphonuclear leukocytes was determined in terms of O2.- generation and elastase release in patients with stable angina (n = 12) and in control subjects (n = 8) after maximal physical exercise and after a 15-min recovery. There was no spontaneous O2.- formation under basal conditions in both groups of patients. On the contrary, there was significant formation of O2.- (p < 0.001) from patients with stable angina measured directly after exercise, along with a slight spontaneous O2.- formation in control subjects (p < 0.05). After recovery, the spontaneous polymorphonuclear leukocyte-O2.- formation decreased but was still present in the patients with stable angina, while in the healthy subjects these values returned to resting levels. The activation of polymorphonuclear leukocytes with phorbol 12-myristate 13-acetate enhanced O2.- formation both in healthy subjects and in patients with stable angina, with a lesser effect in the latter. Moreover, no differences were observed in polymorphonuclear leukocyte-stimulated O2.- formation during the protocol, both in the angina stable patients and healthy subjects. No changes were found in plasma elastase levels among stable angina patients nor in control subjects as a consequence of exercise or recovery. This study indicates there is an early activation of circulating polymorphonuclear leukocytes in terms of O2.- production in stable angina patients during maximal exercise, which is still present after a 15-min recovery. Such activation occurs without elastase release. However, in healthy subjects maximal exercise resulted in very little increase in neutrophil activation.

Neutrophil infiltration into the ischaemic/reperfused rabbit isolated myocardium: effect of PF-5901 and cycloheximide

The Langendorff-perfused rabbit heart preparation has been used to study the interaction of isolated rabbit neutrophils with regionally ischaemic myocardium. Short durations of regional ischaemia (10-60 min) and subsequent reperfusion (30 min) of the hearts with neutrophils resulted in a significant time-dependent accumulation of neutrophils (as assessed by myeloperoxidase activity) in the area at risk. Pre-activation of neutrophils with zymosan-activated serum prior to their infusion into the myocardium potentiated neutrophil accumulation in the area at risk. Pretreatment of the myocardium with a lipoxygenase inhibitor, PF-5901 (10 microM), or a de novo protein synthesis inhibitor, cycloheximide (10 microM), significantly reduced the accumulation of neutrophils in the ischaemic/reperfused myocardium. In contrast, pretreatment of neutrophils with cycloheximide (10 microM, for 15 min) prior to their infusion had no significant effect on neutrophil accumulation in the area at risk. The cyclooxygenase inhibitor, indomethacin (10 microM), had no effect on neutrophil accumulation in the area at risk following ischaemia and reperfusion. These results suggest the involvement of de novo protein synthesis and the lipoxygenase products in the infiltration of neutrophils following ischaemia and reperfusion in vitro.

A prostacyclin analogue reduces free radical generation in heart-lung transplantation

The mechanism by which prostacyclin acts to prevent in vivo reperfusion injury is still uncertain. This study was therefore undertaken to assess the effect of a stable prostacyclin analogue (OP 41483-alpha-CD [OP]) on oxygen-derived free radicals after heart-lung transplantation. OP was administered to the heart-lung graft through the pulmonary artery for 25 minutes encompassing the reperfusion process. Free radicals were directly measured by electron spin resonance spectroscopy. The radical intensities of pulmonary venous blood were significantly lower in the OP group than in the control group, suggesting that fewer free radicals were generated in the lungs of the OP group. The cardiac and respiratory function were better in the OP group than in the control group. The lung is the primary source of oxygen free radical attack, and the beneficial action of OP on free radical generation is almost exclusively restricted to the lung and does not apply to the heart. This result suggested that OP probably is effective in inhibiting free radical generation from the endothelium.

Clinical and experimental aspects of myocardial stunning

Although the mechanisms involved in stunning remain incompletely defined, it appears that intracellular calcium overload, sarcoplasmic reticulum dysfunction, and the generation of OFR are important components of post-ischemic myocyte dysfunction. It is likely that a variety of mechanisms, some possibly remaining to be elucidated, are operative in the pathogenesis of stunning, and that the contribution of a particular process may be influenced by the model and the method of inducing ischemia. Myocardial stunning has been shown to be prevalent in patients with diverse cardiac diseases. Small clinical trials have suggested that electrocardiography, echocardiography, and radionuclide imaging techniques may be useful in identifying patients with stunned myocardium. In patients with depressed cardiac performance due to stunning, therapy with inotropic agents may recruit the viable but injured myocardium to contract and improve cardiac output in the short term. An important issue that will be addressed over the next decade is whether aggressive therapy aimed at reducing myocardial stunning in stable patients should be attempted. Some authorities have suggested that stunning may represent an adaptive response to limit reperfusion injury, and that interfering with this response may not be beneficial in the long term. Further investigation into the cellular and molecular basis of ischemic injury should provide insight into these and other important aspects of myocardial stunning. Methods of attenuating postischemic ventricular dysfunction that appear convincing in the research laboratory may not translate to clinical benefit when applied to humans.

Plasmin generation induces neutrophil aggregation: dependence on the catalytic and lysine binding sites

We established that plasmin (10(-10) M to 10(-6) M) caused neutrophils (PMN) to aggregate using an in vitro assay. Plasminogen had no PMN aggregatory activity even at a concentration of 2 microM. However, plasminogen caused PMN to aggregate when incubated with plasminogen activators [tissue plasminogen activator (25-200 U/ml) or urokinase (5-500 U/ml)]. Tissue plasminogen activator and urokinase alone had no PMN aggregatory activity. Analysis of these incubation mixtures indicated that plasmin was generated in the process and that the time course of plasmin generation correlated with the aggregation response. Active-site-inhibited plasmin did not induce PMN aggregation, indicating that a functional catalytic site was required for the response. Pretreatment of PMN with either active-site-inhibited plasmin or tranexamic acid prevented PMN aggregation by plasmin, indicating that both binding of plasmin to the cell surface via the lysine binding sites and catalysis were required for the response. The generation of plasmin during activation of fibrinolysis may play a pro-inflammatory role by mediating aggregation of PMN.

Mucosal protective effects of vitamin E and misoprostol during acute radiation-induced enteritis in rats

Cytotoxic effects of ionizing radiation on gastrointestinal epithelium may be mediated by oxygen free radicals. Therapeutic intervention directed toward oxidant scavenging and increasing tissue oxygen tension may provide a novel approach to management. We investigated the effects of a nonenzymatic oxygen radical scavenger (vitamin E) and an exogenous PGE1 analog known to increase mucosal blood flow (misoprostol) on acute radiation enteritis. Rats were pretreated with: (1) vitamin E, (2) misoprostol, or (3) a combination of both agents prior to 10 Gy abdominal radiation. Three days following irradiation, net fluid absorption using in vivo isolated loops, mucosal histology, and mucosal morphometry using a computerized videoplan were determined in jejunum, ileum, and colon. Nonirradiated control intestine demonstrated net fluid absorption in all segments, which was not altered by vitamin E and/or misoprostol treatment. Irradiation significantly reduced net fluid absorption in jejunum, ileum, and colon. Vitamin E administered prior to irradiation maintained jejunal, ileal, and colonic fluid absorption near control levels. In contrast misoprostol or a combination of vitamin E and misoprostol did not provide protection against the injury caused by abdominal irradiation. Alterations in intestinal fluid absorption occurred without significant changes in histologic or morphometric appearance. In conclusion, ionizing radiation reduces in vivo intestinal fluid absorption without significant changes in histologic or morphometric appearance. Treatment with vitamin E, but not misoprostol, protects gastrointestinal mucosa against radiation-induced absorptive injury.

Defibrotide inhibits Ca2+ dependent neutrophil activation: implications for its pharmacological activity in vascular disorders

Defibrotide (DEF) is a polydeoxyribonucleotide agent provided with profibrinolytic and antithrombotic properties. Moreover, an antiischemic, cardioprotective effect of the drug has recently been demonstrated in experimental animals. Increasing evidence exists of the important role played by neutrophils in the development of tissue damage during chronic and acute ischemia and in the early phases of reperfusion. In order to evaluate whether the overall cytoprotective effect of DEF could be based, at least in part, on a neutrophil-involving mechanism, the authors studied the in vitro effects of the drug on human neutrophil activation triggered by several specific stimuli. The drug dose-dependently (10-100 microM) inhibited enzyme release, superoxide anion generation, and chemiluminescence induced in neutrophils by the chemoattractant oligopeptide fMLP and by the divalent cation ionophores A23187 and ionomycin. The increase of extracellular calcium concentration from 0.5 to 2.0 mM antagonized the inhibitory effect of DEF. The use of the fluorescent probe Fura 2/AM led them to show that DEF is able to reduce the cytosolic free calcium increase following specific stimulation by affecting extracellular calcium entrance. Such a behavior resembles that of calcium-antagonistic drugs, thus suggesting that DEF works, at least in part, similarly to calcium entry blockers. Such an activity on cell calcium translocation could represent the underlying molecular mechanism of cytoprotection. Finally, the inhibitory action on neutrophil functions may play a role in tissue protection during ischemic injury.

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.

Role of oxygen-derived free radicals in myocardial edema and ischemia in coronary microvascular embolization

BACKGROUND

Oxygen-derived free radicals are thought to injure the ischemic heart during coronary microvascular embolization.

METHODS AND RESULTS

To test this idea, microspheres (15 microns in diameter) were repetitively administered into the left anterior descending coronary artery to cause microvascular embolization in dogs. Myocardial contractile and metabolic dysfunctions were significantly attenuated after treatments with recombinant human superoxide dismutase, an acyl derivative of ascorbic acid (CV3611, 2-O-octadecylascorbic acid), and xanthine oxidase inhibitor (allopurinol). The free radical scavengers and inhibitor enhanced the coronary hyperemic flow response during embolization, and the total number of microspheres causing maximal embolization was increased by these drugs. When 8-phenyltheophylline was additionally administered with superoxide dismutase, these beneficial effects were abolished, indicating that coronary effects of these drugs may be due to increased release of adenosine during coronary microvascular embolization.

CONCLUSIONS

We conclude that oxygen radicals worsen the ischemic injury in coronary microembolization.

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.

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.

Iloprost attenuates the increased permeability in skeletal muscle after ischemia and reperfusion

Increased vascular permeability is an early and sensitive indicator of ischemic muscle injury, occurring before significant histologic or radionuclide changes are evident. We investigated the effect of iloprost, a stable prostacyclin analog, on microvascular permeability in a rat striated muscle model. In six control and six experimental animals the cremaster muscle was dissected, placed in a closed-flow acrylic chamber, and suffused with a bicarbonate buffer solution. Dextran labeled with fluorescein was injected intravenously as a macromolecular tracer, and microvascular permeability was determined on the basis of clearance of the fluorescent tracer. Two hours of ischemia were followed by 2 hours of reperfusion. In the experimental group iloprost (0.5 microgram/kg/min) was given in a continuous intravenous infusion. Microvascular permeability increased significantly during reperfusion in both control and experimental animals (p less than 0.0001). Treatment with iloprost, however, significantly attenuated this response compared to the control group, 4.8 +/- 0.3 versus 7.3 +/- 0.5 microliters/gm/min, respectively (p less than 0.0001). Iloprost decreases the rise in vascular permeability after ischemia and reperfusion. Experimental clinical use of iloprost under controlled conditions in the treatment of patients with acute skeletal muscle ischemia appears justified.

The triphasic pattern of skeletal muscle blood flow in reperfusion injury: an experimental model with implications for surgery on the acutely ischaemic lower limb

A new model of acute lower limb ischaemia has been developed in the rat hind limb. The model has been used to examine the influence on skeletal muscle blood flow of increasing periods of ischaemia and reperfusion. Following restoration of blood flow after 2-6h ischaemia initial gastrocnemius muscle blood flow was reduced. The severity of initial low reflow, indicated by mean perfusion ratios at 0 and 10 min, correlated with the duration of preceding ischaemia (r = 0.83, p less than 0.05) and was greatest in limbs subjected to 6h ischaemia (p less than 0.01 vs. controls at 0, 10 and 60 min after revascularisation). After 60-240 min, reperfusion muscle blood flow returned to normal in limbs subjected to 3, 4 or 5 h ischaemia. In contrast, peak muscle blood flow in limbs that had been ischaemic for 6 h occurred after 120 min, although perfusion remained less than that measured in control limbs (p less than 0.05:6 h ischaemia, 120 min vs. control)-(relative reperfusion). Limbs reperfused after 6 h ischaemia demonstrated a subsequent decline in muscle blood flow between 120 min and 240 min following revascularisation (p less than 0.05). In addition, muscle blood flow at 240 min was no different to that in a totally ischaemic limb (p less than 0.01 vs. controls; ns vs. ischaemic limb) thus representing reperfusion injury.

Effect of iloprost on reperfusion-induced arrhythmias and myocardial ion shifts in isolated rat hearts

Isolated hearts excised from normotensive (NT) and spontaneously hypertensive (SH) rats subjected to transient normothermic global ischemia were used to study the effect of chronic treatment with iloprost on reperfusion-induced arrhythmias and myocardial ion shifts. After 30 min of ischemia, iloprost given s.c. in doses of 10, 50, 100 and 200 micrograms/kg per day for 14 days reduced the incidence of reperfusion-induced ventricular fibrillation (VF) in isolated hearts from the control value of 91 to 83, 75, 50 (P less than 0.05) and 25% (P less than 0.01) respectively, in NT rats. In the SH groups, the incidence of VF was also reduced from 100 to 75, 58, 33 (P less than 0.01) and 17% (P less than 0.001), respectively, with 10, 50, 100 and 200 micrograms/kg per day of iloprost. A similar reduction was observed in the incidence of reperfusion-induced ventricular tachycardia (VT). Ischemia and reperfusion caused significant changes in myocardial ion contents, i.e. an increase in Na+ and Ca2+ and a decrease in K+ and Mg2+ concentrations. The myocardial water content was also increased in parallel to the Na+ gain. The effect of iloprost given s.c. in doses of 50 and 200 micrograms/kg per day for 14 days was also measured on myocardial ion contents after 15- or 30-min ischemia and 30-min ischemia plus 10-min reperfusion. The higher iloprost dose significantly reduced the myocardial Na+, Ca2+ and water gains and the loss of K+ induced by ischemia and reperfusion in the NT and SH groups, while the decrease in Mg2+ content was alleviated only in SH rats. The results suggest that long-term iloprost treatment reduces the incidence of reperfusion-induced VF and VT by preventing Na+, Ca2+ and water accumulation as well as K+ and Mg2+ loss from myocardial tissue.

The relationship between neutrophils and increased microvascular permeability in a model of myocardial ischaemia and reperfusion in the rabbit

1. 111In-labelled neutrophils and 125I-labelled albumin were used to measure neutrophil accumulation and microvascular plasma protein leakage in the ischaemic/reperfused myocardium of anaesthetized rabbits. 2. A period of 30 min coronary artery occlusion followed by 3 h reperfusion resulted in an increase in both 111In and 125I counts in the area at risk (AR) of the myocardium. 3. Pretreatment of 111In-neutrophils in vitro with monoclonal antibody 60.3 directed against the CD18 antigen on neutrophils, followed by intravenous administration, significantly suppressed their accumulation into the AR myocardium. 4. Depletion of circulating neutrophils by use of anti-neutrophil serum or mustine hydrochloride did not affect plasma protein leakage into the AR myocardium. 5. Administration of the platelet activating factor (PAF) antagonist WEB 2086 (10 mg kg-1, i.v.) had no effect on the accumulation of 111In-neutrophils or on plasma protein leakage in the AR myocardium.

Reduced oxidative activity of circulating neutrophils in patients after myocardial infarction

Circulating neutrophils isolated from patients 3-4 h after a myocardial infarction produced less O2-. compared with controls, when stimulated with phorbol myristate acetate or formyl-methionine-leucine-phenylalanine. Three days after the infarction the O2-. generation elicited by both stimuli further decreased markedly. Seven and 15 days after infarction the O2-. stimulated production was only slightly lower than or similar to the control values. The neutrophils of infarcted patients showed an augmented latency period before O2-. production compared with controls in response to exogenous stimuli, particularly three days after infarction. Electron microscopy revealed that the neutrophils isolated from the infarcted patients displayed signs of cell exhaustion with few alterations of the plasma membranes when stimulated with phorbol ester. In contrast, control neutrophils displayed alterations of the plasma membranes characteristic of active neutrophils. The results of this study indicate that the circulating neutrophils appear exhausted and functionally inhibited immediately after myocardial infarction.

Myocardial ischemia, reperfusion and free radical injury

Reperfusion of coronary arteries to limit myocardial ischemic injury and extent of myocardial necrosis is possible by either the use of fibrinolytic therapy, coronary angioplasty or coronary artery bypass surgery. The concept that early reperfusion may salvage jeopardized myocardium is derived from basic experimental studies which purported to demonstrate that the ultimate extent of irreversible myocardial injury could be reduced by reperfusion of the ischemic myocardium within 3 hours from the onset of regional myocardial ischemia. It is firmly established that salvage of ischemic myocardium is dependent on early restoration of blood flow to the myocardium at risk. Despite dependency on reoxygenation for ultimate survival, myocardial tissue that is reperfused and reoxygenated may be subjected to additional injurious insult due to reactive metabolites of oxygen. The cytotoxic species of oxygen are referred to as "oxygen free radicals." Coincident with the influx of inflammatory cells into the reperfused region is an additional loss of otherwise viable myocardial cells. There is strong support for the concept that the polymorphonuclear leukocyte is a contributor to the phenomenon of "reperfusion" or "reoxygenation" injury in the blood perfused heart. This discussion focuses on the role of the neutrophil as a potential contributor to the extension of tissue injury and reviews those interventions, which although in the experimental stage, offer promise of becoming therapeutically important in the future and may help elucidate the mechanisms underlying the potentially deleterious role of the neutrophil in situations involving whole blood reperfusion of the ischemic myocardium.

R,R,R-alpha-tocopherol potentiates prostacyclin release in human endothelial cells. Evidence for structural specificity of the tocopherol molecule

Human umbilical vein endothelial cells (HUVEC) in culture synthesize prostacyclin (PGI2) as the predominant metabolite of arachidonic acid which is derived from the deacylation of phospholipids. Under basal-unstimulated condition, PGI2 release from HUVEC is extremely low; however, when endothelial monolayers were preincubated with the natural vitamin E (R,R,R-alpha-tocopherol), we found a dose-dependent potentiation of basal PGI2 release. When HUVEC were stimulated with arachidonate or ionophore A23187, there was a dose-dependent increase of PGI2 release in response to tocopherol enrichment. When HUVEC were labelled with [Me-3H]choline followed by A23187 stimulation, a significantly higher lysophosphatidylcholine was found in the tocopherol-enriched cells, suggesting a change in enzymes involved in phosphatidylcholine metabolism. Analysis of these enzymes revealed that phospholipase A2 activity was enhanced by tocopherol enrichment, whereas lysophospholipase and acyl-CoA acyltransferase were unaffected. To determine the specificity of the tocopherol molecule, different analogues were tested for their PGI2 potentiating activity. Results showed that the free hydroxyl group on the chromanol ring as well as the phytyl side-chain are absolutely required to stimulate PGI2 release, whereas, different methyl locations and substituents on the chromanol ring had no effect. These studies demonstrated that tocopherol potentiates basal PGI2 release in HUVEC and in contrast to its reported inhibitory role in rat platelets, myocardium and neutrophils, tocopherol stimulates phospholipase activity in HUVEC.

Leukotriene-receptor antagonist FPL-55712 and t-PA-induced thrombolysis in canine coronary thrombosis

Leukocyte-derived arachidonate products peptido-leukotrienes have been shown to induce coronary constriction and platelet aggregation. As such, leukocytes may have a role in coronary thrombosis and coronary re-occlusion following thrombolysis. In the present study, we examined the effects of tissue-plasminogen activator (t-PA, 0.75 mg/kg over 20 minutes) given after either saline or FPL-55712 (2 mg/kg), a peptido-leukotriene receptor antagonist, in dogs with electrically-induced coronary thrombosis. Peripheral blood neutrophil number and superoxide anion generation increased (P less than 0.01) during formation of thrombus and subsequent t-PA administration in saline-treated dogs. FPL-55712 pretreatment attenuated (P less than 0.05) the increase in number of and superoxide anion generation by neutrophils. However, frequency of thrombolysis, duration of restored flow and re-occlusion rates were similar (P-NS) in both groups of dogs. This study shows that FPL-55712 does not modulate the thrombolytic potential of t-PA even though it decreases neutrophil activation in response to myocardial ischemia.

Effects of vitamin E on prostacyclin release and lipid composition of the ischemic rat heart

Free radical-mediated reperfusion injury has been established as an important mechanism leading to post-ischemic reperfusion myocardial damage. The present study was undertaken to determine the protective role of vitamin E, a membrane-bound free-radical scavenger, on ischemia-reperfusion myocardial injury. After 4 months of feeding a semipurified diet containing 0, 30, and 3000 ppm of R,R,R,-alpha-tocopherol acetate, rat hearts were subjected to Langendorff perfusion. Myocardial damage was judged by the release of creatine phosphokinase (CPK) after 45 min of global ischemia followed by 20 min of reperfusion. Effluent CPK was significantly lowered in the two tocopherol-supplemented groups, although increasing dietary vitamin E by 100-fold above requirement did not confer further protection. However, effluent prostacyclin, detected as the stable metabolite 6-keto-PGF1 alpha by radioimmunoassay, was potentiated by dietary vitamin E in a dose-dependent manner. Analysis of lipids in cardiac subcellular fractions showed considerable enrichment of tocopherol in these membranes by diets, but the levels of polyunsaturated fatty acids, phospholipids, and cholesterol were essentially unchanged by dietary treatment or ischemia-reperfusion. These data demonstrated that requirement level of tocopherol (30 ppm) in the diet is sufficient to protect against reperfusion injury of the myocardium and suggests that tocopherol is important in maintaining cardiac prostacyclin synthesis under conditions of oxygen stress.

Oxygen-derived free radicals and postischemic myocardial reperfusion: therapeutic implications

Oxygen-derived free radicals have been implicated in the pathogenesis of various disease states, including myocardial ischemia and reperfusion. In this article, we review 1) the evidence linking free radical production and myocardial injury during myocardial ischemia and reperfusion and 2) results of studies of the effects of the pharmacological therapies available potentially to prevent free radical-mediated injury. Free radicals can be produced during ischemia and reperfusion by several different biochemical pathways. Of these, the xanthine oxidase reaction and the output of free radicals by neutrophils that have accumulated in damaged tissue have been studied extensively. When produced, free radicals can potentially damage myocytes or endothelial cells through peroxidation of membrane lipids or damage to proteins or nucleic acids. Using electron spin resonance spectroscopy, several studies have shown a 'burst' of oxygen free radicals immediately after reperfusion. Moreover, exogenous generation of intravascular free radicals has been shown to produce marked vascular and myocyte damage, as well as contractile dysfunction. 'Anti-free radical' interventions, such as xanthine oxidase inhibitors and free radical scavengers have been reported to prevent contractile dysfunction and reperfusion-induced arrhythmias after an episode of reversible ischemic injury. However, after more severe episodes of ischemia, such interventions have had conflicting effects on myocardial infarct size. 'Anti-free radical' interventions could be of potential use in situations where reversible ischemic injury occurs. In situations where reperfusion is achieved after irreversible ischemic injury has occurred, the potential beneficial effect of these treatments on infarct size is more doubtful.

Prostaglandin redirection by thromboxane synthetase inhibition. Attenuation of myocardial stunning in canine heart

We have previously reported that inhibition of thromboxane synthesis results in an improvement in postischemic function in stunned myocardium of dogs. The purpose of the present study was to investigate further the mechanism by which thromboxane synthesis inhibition improves recovery of function in stunned myocardium (15 minutes of coronary occlusion and 3 hours of reperfusion) in barbital anesthetized dogs. The recovery of regional myocardial wall function (percent segment shortening, % SS) following treatment with two doses (0.5 and 10 mg/kg) of a thromboxane receptor blocker, BM 13.505, given prior to coronary occlusion, was not different from that of a control group (3-hour % SS of pretreatment control, PTC, 12 +/- 11) throughout reperfusion (3-hour % SS of PTC with BM 13.505: 0.5 mg/kg 14 +/- 10; 10 mg/kg, 27 +/- 9). In contrast, the specific thromboxane synthetase inhibitor, dazmegrel (3.0 mg/kg), significantly improved % SS throughout reperfusion (3-hour % SS of PTC, 66 +/- 8). In addition, while dazmegrel produced a marked decrease in thromboxane, 6-keto-PGF1 alpha was significantly increased in coronary venous blood throughout the occlusion and reperfusion period. The cyclooxygenase inhibitor, indomethacin, had no beneficial effect on functional recovery (3-hour % SS of PTC, 5 +/- 6), attenuated the dazmegrel induced shunting to prostacyclin, and completely prevented the beneficial effects of dazmegrel on functional recovery (3-hour % SS of PTC, 17 +/- 12). Thus, a redirection to endogenous cardioprotective prostanoids, such as prostacyclin, appears to be responsible for the beneficial effect of thromboxane synthesis inhibition on postischemic recovery in stunned myocardium whereas thromboxane does not appear to be an important mediator of the stunning phenomenon.

Sustained limitation of myocardial reperfusion injury by a monoclonal antibody that alters leukocyte function

Pentobarbital anesthetized dogs were subjected to 90 minutes of left circumflex coronary artery (LCCA) occlusion followed by 72 hours of reperfusion. Control or anti-Mo1 (904) F(ab')2 fragments of monoclonal antibodies were administered intravenously at a dose of 1 mg/kg beginning 45 minutes after occlusion and at a dose of 0.5 mg/kg at 12, 24, 36, and 48 hours after reperfusion. Myocardial infarct size expressed as a percentage of the area at risk (IN/AR) measured postmortem after 72 hours of reperfusion was significantly reduced by 904 F(ab')2 (21.6 +/- 2.8%, n = 8) compared with control F(ab')2 (37.4 +/- 5.8%, n = 8; p less than 0.025). There were no significant differences between groups in heart rate, mean arterial blood pressure, rate-pressure product, or LCCA blood flow that could account for a reduced infarct size. Regional myocardial blood flow (RMBF) was determined with 15-microns radiolabeled microspheres. Transmural blood flows (ml/min/g) within the region of myocardium at risk were not statistically different between treatment groups. Infarct size in both groups was related to regional myocardial blood flow, and the relation was shifted downward in the group treated with the anti-Mo1 F(ab')2 antibody (analysis of covariance, p = 0.01). Thus, anti-Mo1 F(ab')2 produces a sustained limitation of myocardial infarct size compared with controls under similar hemodynamic conditions and a similar degree of myocardial ischemia as determined by RMBF. These data suggest that inhibition of neutrophil adhesive interactions (as suggested by the inhibitory effect of anti-Mo1 on canine neutrophil aggregation) may be an effective mechanism for protection against myocardial injury secondary to myocardial ischemia and reperfusion.

Neutrophil depletion limited to reperfusion reduces myocardial infarct size after 90 minutes of ischemia. Evidence for neutrophil-mediated reperfusion injury

Reperfusion of ischemic myocardium may accelerate necrosis of injured myocytes. To determine the role of neutrophil leukocytes in this process, we examined whether neutrophil depletion during reperfusion could modify infarct size in anesthetized dogs. The proximal circumflex coronary artery was occluded for 90 minutes and then reperfused for 2 hours via an extracorporeal circuit with either whole blood (n = 11) or with blood depleted of neutrophils by leukocyte filters (n = 11). The leukocyte filters caused near-total neutropenia in blood reperfusing the ischemic myocardium (7 +/- 7 neutrophils/microliters compared with 2,551 +/- 317/microliters in controls, mean +/- SEM; p less than 0.001. Infarct size was measured by planimetry of myocardial slices stained with triphenyltetrazolium chloride (TTC), and the accuracy of TTC for identifying necrotic myocardium was verified by electron microscopy. The size of the ischemic risk region was the same in the control (41.6 +/- 1.0%) and neutropenic (41.8 +/- 2.1%) groups. Collateral blood flow to the risk region was the same in control (0.15 +/- 0.03 ml/min/g) and neutropenic (0.13 +/- 0.03 ml/min/g) groups. Among dogs with collateral flow less than 0.2 ml/min/g, infarct size was reduced in the neutropenic group (27.7 +/- 6.7% of risk region, n = 8), compared with control dogs (52.5 +/- 5.7%; n = 7; p = 0.02). Multiple linear regression described the relation between infarct size, risk region size, and collateral flow in the control group, and the same regression relation was used to predict infarct size for the neutropenic group. Mean predicted infarct size in the neutropenic group (n = 11) was 16.8 +/- 3.4% of left ventricle, whereas mean observed infarct size was 9.6 +/- 3.1% (p less than 0.01). The extent of the no-reflow zone (absence of thioflavin-S-fluorescence) was also less in the neutropenic than the control group (2.2 +/- 0.8% vs. 8.1 +/- 2.7% of the risk region, p less than 0.05). Neutropenia limited to the reperfusion period is associated with significant reductions in the extent of the infarct and no-reflow zones after 90 minutes of ischemia. These findings support the hypothesis that reperfusion necrosis occurs after prolonged myocardial ischemia and indicate that neutrophil leukocytes are important mediators of such reperfusion injury.

Dexamethasone attenuates microvascular ischemia-reperfusion injury in the rat cremaster muscle

We examined the effect of dexamethasone (DXM) pretreatment on microvascular transport of macromolecules in ischemia-reperfusion injury. The rat cremaster muscle was splayed, placed in a Lucite intravital chamber, and suffused with bicarbonate buffer. The clearance of fluorescein isothiocyanate-dextran 150 (FITC-Dx 150) was measured as an index of microvascular transport. After determination of baseline data, the muscle was made ischemic for 2 hr by clamping its vascular pedicle, and subsequently reperfused for 2 hr. Ischemia-reperfusion produced a marked increase in clearance of FITC-Dx 150. After an initial peak of 13 times baseline value clearance fell to approximately 4 times baseline level 30 min into the reperfusion period. Clearance increased slowly throughout the remainder of the experiment, reaching 6 times baseline after 2 hr of reperfusion. The treated animals received DXM 3 hr prior to and immediately preceding the pedicle clamping. DXM reduced macromolecular clearance significantly after the first 30 min of reperfusion, and prevented the increase in clearance over time. After an initial peak, clearance values fell to near twice baseline in DXM-treated animals, and remained at this level for the 2 hr of reperfusion. Our data demonstrate that DXM attenuates the alternations in microvascular macromolecular transport produced by ischemia-reperfusion injury.

Attenuation of no-reflow phenomenon, neutrophil activation, and reperfusion injury in intestinal microcirculation by topical adenosine

Small mesenteric arteries supplying partially isolated jejunal segments were totally occluded for 5 minutes and then released. With video microscopy, blood flow was calculated from measurements of submucosal arteriolar diameter and red blood cell velocity. For the first 30 minutes of reperfusion, the serosa was superfused with a Ringer's vehicle containing either adenosine (ADO; 10(-4) M), acetylcholine (ACh; 10(-5) M), or prostacyclin (PGI2; 3 x 10(-7) M). Thereafter, the substances were removed from the suffusate, and superfusion continued with vehicle alone for an additional 10-30 minutes. These concentrations were equieffective for causing vasodilation. During the first minute of reperfusion, blood flow increased more than 300% of baseline in all groups. Within the subsequent 30 minutes, blood flow fell to 45 +/- 3% of baseline with vehicle alone, which demonstrates the no-reflow phenomenon. While either ADO, ACh, or PGI2 was in the suffusate, vasodilation was persistent. After washout of these substances, the postocclusion blood flows were significantly higher with each treatment than with vehicle alone, which shows that each substance had a positive action. However, with ADO, blood flow was 121 +/- 7% of baseline after washout, whereas with ACh or PGI2, it was 64 +/- 10% or 69 +/- 5% of baseline after washout. This property of ADO was observed if the mucosa was superfused with a Ringer's solution or with a bile salt solution, which suggests that ADO might have similar properties in situ. After 60 minutes of reperfusion, the intestinal villi were short, thick, and edematous with epithelial necrosis and crypt degeneration. ADO attenuated most of these histological changes to a greater extent than either PGI2 or ACh. Furthermore, ADO reduced a biochemical index of neutrophil infiltration; tissue myeloperoxidase concentration was increased to 169 +/- 14% of baseline with vehicle but was increased to 120 +/- 8% with ADO. Overall, these observations suggest that ADO protects the intestine from ischemia-reperfusion injury by causing vasodilation and by inhibiting neutrophil function. The vasodilatory effect probably is a minor component because other vasodilators (ACh and PGI2) had minimal protective effects in these conditions.

Prostaglandin E1 attenuates postischemic contractile dysfunction after brief coronary occlusion and reperfusion

We have previously demonstrated that administration of the prostacyclin analogue iloprost improved postischemic functional recovery in reversibly injured ischemic-reperfused myocardium. The present study investigated the effects of administering an endogenous vasodilator prostanoid, prostaglandin E1 (PGE1), in the stunned myocardium (15 minutes of coronary artery occlusion and 3 hours of reperfusion) of anesthetized dogs. The percentage of regional myocardial segment shortening (%SS) after administration of PGE1 by two routes, intravenously (1 microgram/kg/min) or intraatrially (0.1 microgram/kg/min), to avoid pulmonary metabolism, 15 minutes before and throughout the period of occlusion, was compared to %SS in a control group treated with saline solution. Nearly equivalent reductions in mean arterial pressure during occlusion compared to pretreatment control (PTC) values were produced by intravenous (33%) or intraatrial (25%) PGE1. There was no difference in transmural myocardial blood flow (radioactive microsphere technique) in the ischemic region between the PGE1-treated and control groups at any time. Although there were no differences in %SS in the nonischemic region between groups throughout the experiment, postischemic recovery of segment function in the ischemic-reperfused area was significantly improved (p less than 0.05) at all times during reperfusion by intravenous PGE1 (%SS of PTC: 30 minutes = 65 +/- 8; 3 hours = 58 +/- 7) or intraatrial PGE1 (%SS of PTC: 30 minutes = 57 +/- 12; 3 hours = 50 +/- 4) compared to the control group (%SS of PTC: 30 minutes = 25 +/- 13; 3 hours = 10 +/- 13). Thus treatment with PGE1 attenuates postischemic contractile dysfunction in the stunned myocardium.2+ both.