Joseph L. Romson

The effect of dietary supplementation of fish oil on experimental myocardial infarction

The effect of altering the abundance of precursors and inhibitors of prostaglandin formation by dietary supplements of fish oil was investigated in dogs with experimentally induced myocardial infarction. Prior to induction, 10 male mongrel dogs were fed standard dog chow supplemented with 25% of the total calories as menhaden oil for 36 to 45 days. The fatty acid composition of th lipids in plasma and platelets changed to reflect the increased intake of polyunsaturated fatty acids of the n-3 type. Thrombosis and subsequent infarction was induced by electrical stimulation of the left circumflex coronary artery of ambulatory dogs that were monitored by telemetry. Upon stimulation of control animals, the frequency of ectopic beats rose from less than 10% at the beginning to about 80% after 19 hours. In contrast, the oil-fed dogs maintained a more normal ECG pattern, showing less than 30% ectopic beats after 19 hours. In these animals, the size of infarction (measured by formazan formation) was 3% of the left ventricle compared to 25% in the control animals. The results suggest that dietary supplementation with fish oil may be beneficial in reducing myocardial damage associated with coronary artery thrombosis.

Electrical induction of coronary artery thrombosis in the ambulatory canine: A model for in vivo evaluation of anti-thrombotic agents☆

Abstract A simple technique for the reliable induction of coronary artery thrombosis in a conscious dog by delivery of low amperage electric current to the intimal surface of the artery is described. Ibuprofen, an agent known to inhibit platelet function and prostaglandin synthesis is evaluated in this model. Comparison of myocardial infarct size, thrombus weight, arrhythmia development and scanning electron micrographs of drug treated and control animals indicate that Ibuprofen is capable of protecting against the deleterious effects of coronary artery thrombosis produced by this technique. This method holds considerable potential as an in vivo model of coronary artery thrombosis and one in which evaluation of anti-thrombotic agents is possible.

Effects of Diltiazem on Extent of Ultimate Myocardial Injury Resulting from Temporary Coronary Artery Occlusion in Dogs

Summary The calcium antagonist, diltiazem, was evaluated for its ability to reduce the extent of myocardial injury resulting from 90 min of left circumflex (LCX) coronary artery occlusion in anesthetized dogs. Administration of diltiazem (0.75 mg/kg over 10 min, followed by 600 μg/kg/h for 4 h) was initiated 30 min prior to LCX occlusion. Regional myocardial blood flow (RMBF) was measured with radioactive microspheres 30 min after LCX occlusion, and at 45 min and 24 h after reperfusion. At 24 h, after obtaining hemodynamic and RMBF measurements, excised hearts were processed by perfusion staining to determine the percent of left ventricle (LV) perfused by LCX (area at risk) and infarct size, with triphenyltetrazolium chloride. Infarct size, expressed as a percentage of the area at risk, was significantly lower in the diltiazem-treated group compared to the control group (27 ± 4 vs. 42 ± 5%, respectively). The area at risk, expressed as a percentage of left ventricular mass, was similar in both groups [41 ± 2 and 44 ± 3% (area at risk—LV)]. In addition, the marked elevation of tissue Ca2+ content in noninfarcted and infarcted myocardium within the area at risk (18 ± 2 and 42 ± 8 μmol Ca2+/g) in control animals was attenuated by diltiazem (6 ± 3 and 18 ± 8 μmol Ca2+/g). Diltiazem did not increase blood flow to ischemic myocardium during LCX occlusion. However, reflow to the inner layers of formerly ischemic myocardium during reperfusion was significantly greater in diltiazem-treated dogs. Both arterial blood pressure and heart rate were significantly lower in the diltiazem-treated group. In addition, mortality (1 vs. 4) and occurrence of ventricular arrhythmias during reperfusion were lower in diltiazem-treated dogs. The data suggest that diltiazem reduces myocardial ischemic injury by lowering myocardial oxygen demands indirectly via favorable hemodynamic alterations, and directly by limiting transmembrane Ca2+ fluxes during ischemia and reperfusion.

Prostaglandins and Prostaglandin Inhibitors in Ischemic Heart Disease

The evidence for a role of the prostaglandin system in myocardial ischemia and its consequences is still fragmentary. We review the factors that alter the relation between thromboxane A2 and prostacyclin production such that vasoconstriction, platelet aggregation, and the tendency toward thrombus formation are increased. Strategies to prevent platelet aggregation by interfering with the production of thromboxane A2 or by stimulation or administration of prostacyclin are currently under investigation in a number of centers. The ubiquity of the prostaglandin system and our incomplete understanding make careful long-term clinical trials and observations essential if we are to be sure that the net effect of these attempts is beneficial.

Cardioprotective effects of ibuprofen in experimental regional and global myocardial ischemia

Summary The effects of the nonsteroidal antiinflammatory agent, ibuprofen, were evaluated in two animal models of myocardial ischemia: regional myocardial ischemia produced by temporary occlusion followed by reperfusion of the canine left circumflex coronary artery (LCX), and global ischemia in the isolated, blood-perfused feline heart. In control dogs (n = 12), 60 min of LCX occlusion followed by 24 h of reperfusion resulted in 51 ± 4% of the area at risk, and 20 ± 2% of the total left ventricle becoming infarcted. The average infarct size of the group of dogs receiving oral ibuprofen (n = 12: dose of 12.5 mg/kg, q4h) was 33 ± 5% of the area at risk, and 12 ± 2% of the total left ventricle, a reduction in infarct size as compared to the controls of 35% (p > 0.02) and 39% (p < 0.02), respectively. The mechanism by which ibuprofen provided these beneficial effects could not be attributed to a reduction in myocardial oxygen consumption (M&OV0312;O2), estimated by rate–pressure products, or redistribution of regional myocardial blood flow, assessed by radioactive microspheres. The direct effect of ibuprofen on ischemic myocardium was assessed in an isolated, blood-perfused cat heart model of global ischemia. After 60 min of normothermic global ischemia, left ventricular pulse pressure of control hearts (n = 8) at 5 and 10 mm Hg end-diastolic pressure was reduced by 56 ± 97% and 60 ± 12%, respectively, relative to preischemic values. Administration of ibuprofen (12.5 mg/kg, i.v., to the blood donor cat, n = 6) did not significantly prevent the ischemia-induced deterioration of left ventricular function. Normothermic ischemia for 60 min resulted in a significant reduction in M&OV0312;O2 in both the control and ibuprofen-treated hearts. However, after 1 h of reperfusion, the average M&OV0312;O2 for the ibuprofen-treated hearts was 96% greater (4.5 ± 0.4 versus 2.3 ± 0.5 ml/min/100 g) than the average M&OV0312;O2 of the control hearts. While conventional thinking contends that myocardial infarct size may be limited by a reduction in M&OV0312;O2 or a redistribution of blood flow, the data from this study indicate that these two mechanisms are not relevant in the case of ibuprofen.

Effects of lodoxamide on ischemic reperfused myocardium

The beneficial effects of lodoxamide tromethamine (U42585E) have been examined in a canine model of myocardial ischemic injury. Lodoxamide was infused 20 mg/kg/h i.v. starting 30 min before occlusion of the proximal left circumflex coronary artery (LCX) and continuing through 90 min of ischemia. Lodoxamide produced a significant reduction in ultimate infarct size measured at 24 h by postmortem tetrazolium perfusion staining. Infarct size expressed as a percent of the anatomical area at risk was 21.7 ± 2.7 in the treated group vs. 47.0 ± 3.1 in the control group (mean ± SEM). No significant difference in area at risk was observed between treated and control groups. Salvage occurred primarily in subepicardial and midmyocardial tissue without apparent lateral protection. Histological examination confirmed gross results of postmortem staining. The protection appeared to be unrelated to myocardial oxygen demand since no hemodynamic differences between groups were observed at the time of occlusion or throughout the 24-h experimental course. Concurrent studies of ex vivo platelet aggregation showed no effect of lodoxamide on adenosine diphosphate (ADP), collagen, and arachidonic acid-induced aggregation. In vivo antithrombotic effects were evaluated in four conscious dogs by inducing LCX thrombosis with low-amperage stimulation (50 μA for 24 h) of the intimal surface. Occlusive thrombi occurred in all four dogs and were similar to controls. These results suggest that lodoxamide reduces myocardial ischemic injury by a mechanism unrelated to oxygen demand or antiplatelet effects.

Prevention of occlusive coronary artery thrombosis by prostacyclin infusion in the dog.

The hemodynamic and antithrombotic properties of prostacyclin (PGI2) were evaluated in an in vivo canine model in which left circumflex coronary artery (LCX) thrombus formation was initiated by electrical stimulation (150 iA, DC for 6 hours) of the arterys intimal surface via an implanted silver wire electrode. Eleven of the 12 control dogs (92%) developed totally occlusive LCX thrombi after an average of 3.2 + 0.4 hours of LCX stimulation; the remaining control dog underwent spontaneous ventricular fibrillation.A PGI2 infusion (150, 300 or 500 ng/kg/min) into the left atrial appendage was begun 10 minutes before the start of LCX stimulation and continued throughout the 6-hour stimulation period. LCX thrombus wet weight and the incidence of occlusive LCX thrombosis decreased in the PGI2-treated dogs in a dose-dependent manner. Hemodynamically, after 6 hours of PGIs infusion at 500 ng/kg/min, mean arterial pressure decreased by 36 ± 4%, cardiac output increased by 51 ± 14%, and the effect on heart rate was inconsistent. Light and scanning electron microscopic examination of the LCX at the site of electrode insertion in PGI2- treated dogs (500 ng/kg/min) revealed a damaged and denuded. intimal surface but no thrombi, in contrast to the thrombus formation in similar specimens taken from control dogs. In this report, we describe the potent hemodynamic effects of prolonged PGI2 infusion and demonstrate its ability to prevent coronary artery thrombosis in response to intimal injury.

Ibuprofen-mediated infarct size reduction: Effects on regional myocardial function in canine myocardial infarction

Normal, marginal, and central ischemic regional myocardial function were evaluated in a canine model of myocardial infarction during 90 minute left circumflex coronary artery occlusion in 25 anesthetized dogs randomly assigned to intravenous ibuprofen infusion (n = 13,5.36 mg/kg/h beginning 1 hour before occlusion) or vehicle solution as control (n = 12) and in 15 conscious, unsedated dogs 48 and 72 hours after 90 minute circumflex artery occlusion followed by reperfusion (ibuprofen, 5.36 mg/kg/h by intravenous infusion over 7 hours beginning 1 hour before occlusion, n = 7; or vehicle solution infusion as control, n = 8). Miniature subendocardial sonomicrometer crystal pairs were used to calculate left ventricular regional end-diastolic segment length, end-systolic segment length, and regional percent systolic shortening. Infarct size was estimated in 72 hour animals by a postmortem dual perfusion technique using triphenyltetrazolium histochemical dye and Evan’s blue dye for determination of infarct area, risk area, and area not at risk. Ibuprofen treatment significantly reduced infarct size expressed as percent of risk area (mean f standard deviation of 44.6 f 18 versus 64.4 f 16% for control dogs, p <0.05) but it did not improve normal, marginal, or ischemic region end-diastolic length, end-systolic length or percent systolic shortening during coronary occlusion in anesthetized dogs or after reperfusion in conscious animals at 48 and 72 hours, and it did not enhance inotropic reserve at 72 hours in conscious animals. During 90 minute circumflex occlusion in anesthetized dogs, ibuprofen was associated with increases in systemic arterial pressure and worsened ischemic regional percent systolic shortening. Thus, ibuprofen does not improve normal, marginal, or ischemic zone regional myocardial function during acute ischemia or 48 or 72 hours after myocardial reperfusion despite a significant reduction of infarct size.

The beneficial effects of nafazatrom (BAYg6575) on experimental coronary thrombosis

An in vivo model of coronary artery thrombosis in the conscious dog was used to evaluate the potential antithrombotic effect of nafazatrom (BAYg6575). A silver wire electrode was implanted in the left circumflex coronary artery (LCX) and was used at a later time to deliver a 50 uA anodal current for 24 hours to the intimal surface of the vessel. The resulting injury to the endothelium was accompanied by the adhesion, aggregation, and subsequent formation of an occlusive thrombus in the LCX of vehicle-treated dogs. Nafazatrom was given as an intravenous dose of 1 mg/kg for 48 hours, before anodal stimulation of the coronary artery was initiated, and was repeated every 6 hours during anodal stimulation for a total treatment period of 72 hours. As compared to vehicle-treated control dogs, the dogs treated with nafazatrom had smaller thrombi, preservation of coronary blood flow, a lesser degree of ischemic injury in the myocardial region subserved by the LCX, and less frequent premature ventricular complexes during the final 12 hours of the study period. Concomitant ex vivo platelet aggregation studies revealed significant inhibition of platelet aggregation in response to collagen and adenosine diphosphate in drug-treated dogs. The results of these investigations provide evidence that nafazatrom prevents in vivo development of occlusive coronary artery thrombi in response to disruption of the endothelial surface of the vessel.

Identification of Hydrogen Peroxide and Hydroxyl Radical as Mediators of LeukocyteInduced Myocardial Dysfunction

Neutrophil infiltration of the myocardium is an important component of such diverse disease entities as myocarditis, ischemia, and ischemia-reperfusion injury. We have hypothesized that activated neutrophils are capable of disrupting myocardial function via an oxygen free-radical mechanism. Human neutrophils activated with phorbol myristate acetate disrupted calcium transport by canine cardiac sarcoplasmic reticulum, and this process was inhibited by a combination of superoxide dismutase and catalase. In addition, the activated neutrophil system was also inhibited by the combination of cyclooxygenase inhibitors (ibuprofen and indomethacin) and catalase and accelerated by MK-447. These results incriminate both hydrogen peroxide and the hydroxyl radical as mediators of neutrophil-induced myocardial dysfunction. A test of this hypothesis in vivo was performed by neutrophil-depleting dogs with anti-canine leukocyte antisera prior to coronary artery ligation. Following 6 hr of reperfusion, there was a 43% reduction in infarct size compared to non-immune-sera-injected animals. We conclude that oxygen free radicals generated by neutrophils are capable of inducing significant myocardial injury and play an important role in the pathophysiology of ischemia-reperfusion injury.