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Biomedical subjects

M B Forman

Publications and source records attributed to M B Forman.

At least 19 recordsLinked to original sources
PubMed2000

Sustained reduction in myocardial reperfusion injury with an adenosine receptor antagonist: possible role of the neutrophil chemoattractant response.

Recent studies have demonstrated that three membrane-permeant A(1) receptor antagonists reduced infarct size in a model of ischemia followed by brief reperfusion. However, it was not determined whether cardioprotection was mediated by nonspecific intracellular effects of these highly lipophilic drugs and whether the antagonists only delayed myocardial necrosis without affecting the ultimate infarct size. In the present study, closed-chest dogs were subjected to 90 min of left anterior descending coronary artery occlusion and 72 h of reperfusion and received either a nonmembrane-permeant adenosine receptor blocker that is devoid of direct intracellular effects and is 6-fold selective for the A(1) receptor [1, 3-dipropyl-8-p-sulfophenylxanthine (DPSPX); n = 11] or vehicle (n = 12). DPSPX was administered as three 200-mg boluses 60 min before and 30 and 120 min after reperfusion. The area of necrosis was determined histologically and expressed as a percentage of the area at risk. Baseline predictors of infarct size were similar in the two groups. The ratio of the area of necrosis to the area at risk was less in the DPSPX group (17.8 +/- 4.3% versus 35.0 +/- 1.9%; P =. 012), and DPSPX improved regional ventricular function. Under both basal and stimulated (formyl-Met-Leu-Phe) conditions, suspensions of human neutrophils generated extracellular adenosine levels (approximately 50 nM) sufficient to activate A(1) receptors. Moreover, both DPSPX and 1,3-dipropyl-8-cyclopentylxanthine, a selective A(1) receptor antagonist, significantly reduced the chemoattractant response of neutrophils to formyl-Met-Leu-Phe. We conclude that blockade of A(1) adenosine receptors attenuates myocardial ischemic/reperfusion injury, possibly in part by decreasing the chemoattractant response of neutrophils.

Animals↗
PubMed1997

Reduction of myocardial infarct size in rabbits and inhibition of activation of rabbit and human neutrophils by lidocaine.

Myocardial reperfusion is associated with increased influx of activated neutrophils and intracellular accumulation of sodium in the ischemic zone. Lidocaine is a sodium channel blocker that also inhibits several neutrophil functions. We investigated the effect of lidocaine on infarct size in rabbits undergoing 30 minutes of ischemia and 48 hours of reperfusion. Animals randomly received lidocaine (10 mg/kg, n = 11) or saline (n = 11) during occlusion. The area of necrosis (AN) was measured histologically and expressed as a percentage of the area at risk (AR). Myocardial oxygen consumption and the perfusion bed at risk were similar in the two groups. Lidocaine reduced infarct size compared with control (AN/AR = 30% +/- 4% vs 61% +/- 5%, respectively; p = 0.0001). This reduction was associated with a significant decrease in neutrophil infiltration and in the degree of hemorrhage in the reperfused myocardium. Lidocaine also significantly inhibited superoxide anion production by rabbit and human neutrophils in whole blood. Therefore, lidocaine treatment results in a significant reduction in infarct size in the rabbit model, partly through reduction of neutrophil-mediated injury to viable cells, suggesting that lidocaine may be useful to enhance myocardial salvage in patients undergoing pharmacologic or mechanical reperfusion.

Animals↗
PubMed1996

Role of endothelin in a rabbit model of acute myocardial infarction: effects of receptor antagonists.

The role of endothelin (ET) in acute myocardial infarction and proarrhythmic potential was investigated in a rabbit model. One group of rabbits underwent 30 min of circumflex occlusion and 3 h of reperfusion with measurements of myocardial blood flow and myocardial levels of ET-1 messenger RNA (mRNA). In a second group, the systemic and coronary effects of exogenous ET were studied in animals pretreated with either saline, FR139317, an ETA-receptor antagonist, or PD145065, an ETA-and ETB-receptor antagonist. In a third study, animals undergoing 30 min of circumflex occlusion followed by 48 h of reperfusion were treated with exogenous ET-1, FR139317, PD145065, or saline. Arrhythmias were recorded and infarct size measured at 48 h. These studies revealed that ischemia and reperfusion was followed by a progressive microcirculatory failure ("no-reflow phenomenon") in rabbits. This was associated with a 2.6-fold elevation in levels of myocardial ET-1 mRNA in the ischemic zone in comparison to the nonischemic zone (p = 0.04). Exogenous ET-1 caused elevation in coronary and systemic vascular resistance that was significantly blocked by antagonism of the ETA receptor. In rabbits subjected to myocardial ischemia and reperfusion, ET-1 infusion led to a higher incidence of ventricular arrhythmias, whereas ET-receptor antagonism with PD145065 significantly reduced ventricular arrhythmias. Exogenous ET-1 and FR139317 failed to alter infarct size (AN) of the area at risk (AR) compared with control [AN/AR(%) was 46 +/- 8, 55 +/- 9, and 47 +/- 7, respectively]. However, PD145065 significantly decreased AN/AR (22 +/- 7; p < or = 0.02). The increased production of ET-1, resulting from increased levels of mRNA after reperfusion, may contribute to the no-reflow phenomenon. Although the vasoconstrictor effects of ET-1 can be blocked by ETA-receptor antagonism alone, only blockade of both the ETA and ETB receptors significantly reduced infarct size. These data suggest that production of ET increases in the heart during ischemia and is deleterious to the reperfused myocardium.

Animals↗
PubMed1994

Reperfusion enhances the local release of endothelin after regional myocardial ischemia.

The role of endothelin, a potent long-acting vasoconstrictor peptide, in the pathogenesis of the "no-reflow" phenomenon was investigated in nine closed-chest mongrel dogs undergoing 90 minutes of proximal left anterior descending artery occlusion and 3.5 hours of reperfusion. Endothelin levels were measured serially from the coronary sinus (CS) and aorta (Ao) by radioimmunoassay and correlated with regional myocardial blood perfusion. Prolonged anesthesia, surgery, and vascular instrumentation did not change endothelin levels in four sham animals. A progressive and parallel increase in CS and Ao endothelin levels occurred during coronary occlusion. A further increase in CS levels was observed during the reperfusion period, resulting in significantly higher values of the peptide at 30 and 60 minutes (30 minutes: CS 22.1 +/- 3.5 vs Ao 15.1 +/- 5.1 pg/ml; 60 minutes: CS 21.1 +/- 4.5 vs Ao 15.0 +/- 3.6 pg/ml; p < 0.05 by analysis of variance). Microvascular perfusion determined semiquantitatively with fluorescent beads was significantly reduced in the central ischemic zone (CIZ) compared with that in the nonischemic zone (NIZ) (CIZ endocardium 1.14 +/- 0.4 beads/m2, CIZ midmyocardium 1.19 +/- 0.3 beads/m2, NIZ 3.8 +/- 0.6 beads/m2; p < 0.05). A significant correlation was noted between mean reperfusion levels of endothelin in the CS and endocardial flow in the CIZ (r = -0.88; p = 0.009). This study demonstrates that reperfusion per se enhanced the spillover of endothelin from the cardiac interstitium. Local release of endothelin may contribute to the progressive decrease in microvascular flow in the reperfused bed.

Animals↗
PubMed1993

Intravenous adenosine suppresses cardiac release of endothelin after myocardial ischaemia and reperfusion.

OBJECTIVE: Intravenous adenosine decreases infarct size in experimental models of myocardial ischaemia/reperfusion. Ischaemia/reperfusion is associated with a significant increase in cardiac release of endothelin. The effect of cardioprotective doses of adenosine on endothelin release was explored in dogs undergoing 90 min coronary occlusion and 210 min reperfusion. METHODS: Dogs were assigned to intravenous adenosine in a dose of 0.15 mg.kg-1.min-1 (n = 12) or control (n = 11) during the first 150 min reperfusion. Serial endothelin levels were obtained from the coronary sinus and aortic blood and measured by radioimmunoassay. RESULTS: Adenosine significantly reduced infarct size expressed as a percent of the risk region (28.8 6% v 14.4 2%; p = 0.03). A similar increase in aortic and coronary sinus blood endothelin was observed in both groups during temporary occlusion. A significant transcardiac increase in endothelin levels was present in the control group 60 min after reperfusion whereas no increase occurred in the adenosine treated group [control 5.6(SEM 1.9) v adenosine -0.2(1.4) pg.ml-1; p = 0.02]. Similarly, intravenous adenosine tended to prevent the increase in myocardial endothelin production seen in control animals during the early reperfusion period [control 280(146) v adenosine -57(55) pg.min-1; p = 0.05]. Endocardial blood flow in the ischaemic zone 210 min after reperfusion was significantly higher in the adenosine group, at 0.60(0.02) v 0.38(0.02) ml.min-1.g-1; p < 0.05. A significant correlation between endothelin levels, endocardial flow and infarct size was observed in the control group 3 h after reperfusion: r = 0.73, p = 0.02; r = 0.62, p = 0.03 respectively. This relationship was absent in animals treated with adenosine. CONCLUSIONS: Intravenous adenosine suppresses the release of endothelin from the previously ischaemic myocardium during the early reperfusion period. This effect may in part contribute to the improvement by adenosine in postischaemic microcirculatory flow resulting in attenuation of the "no reflow" phenomenon.

Adenosine↗
PubMed1993

Activation of complement by Fluosol attributable to the pluronic detergent micelle structure.

Fluosol, a complex mixture of perfluorocarbons with a high oxygen-carrying capacity emulsified with the detergent pluronic F-68 and various lipids, recently was approved for adjuvant therapy to reduce myocardial ischemia during coronary angioplasty. Anaphylactoid reactions after Fluosol infusion through activation of the complement pathway have been reported in some patients. We examined the mechanism of complement activation by Fluosol. In vitro, incubation of both dog and human plasma with Fluosol for 1 h caused a significant reduction in total hemolytic complement levels (CH50). None of the individual components of Fluosol tested activated complement. A reduction in CH50 levels similar to that observed with Fluosol was obtained after incubation of dog or human plasma with the detergent pluronic F-68 in combination with either perfluorocarbon. In vivo, a bolus injection of the detergent and perfluorocarbon fully mimicked the anaphylactoid reaction of Fluosol previously observed in dogs, with transient profound hypotension, tachycardia, and reduction in CH50 levels occurring < or = 5 min. To investigate further the mechanism by which the pluronic/perfluorocarbon combination activates complement, an inert dense liquid (mineral oil or silicon oil) substituted for the perfluorocarbons produced comparable complement activation both in vitro and in vivo. These observations suggest that creation of a larger pluronic micelle around a core of perfluorocarbons or any inert dense substance, causes formation of a specific surface configuration, resulting in activation of the complement cascade.

Animals↗
PubMed1993

Focal pulmonary embolism presenting as diffuse pulmonary edema.

We report the unique occurrence of bilateral pulmonary edema in a patient with a small focal pulmonary embolus without evidence of underlying cardiac or pulmonary disease. The most likely mechanism for this involves the release of humoral factors leading to extravasation of fluid across pulmonary capillary membranes. This case illustrates that pulmonary emboli should always be considered in the differential diagnosis of pulmonary edema.

Female↗
PubMed1992

Role of perfluorochemical emulsions in the treatment of myocardial reperfusion injury.

Perfluorochemicals are substances with small particle size, low viscosity, and high oxygen-carrying capacity. The role of one perfluorochemical preparation. Fluosol, an emulsion of two perfluorocarbons, a detergent Pluronic F-68 (poloxamer 188), and phospholipids on myocardial reperfusion injury was investigated in a closed-chest canine model of regional ischemia. Intracoronary and intravenous infusions of Fluosol in the perireperfusion period significantly reduced infarct size and improved ventricular function in animals that were examined for up to 2 weeks after reperfusion. Fluosol preserved endothelial structure and endothelium-dependent relaxation of large and small vessels. Fluosol reduced neutrophil plugging of capillaries and attenuated neutrophil infiltration into the reperfused bed. Ex vivo studies of neutrophil function demonstrated apparent suppression of chemotaxis and lysozyme degranulation in cells from animals that were treated with Fluosol. However, treatment of cells in vitro manifested enhanced superoxide anion production within 5 minutes of incubation even with low concentrations of Fluosol. This effect was found to be almost entirely attributable to the detergent, Pluronic F-68. The stimulation of neutrophils by Fluosol was found to result directly from phagocytosis and indirectly from activation of the complement cascade. These findings suggest that perfluorochemicals may provide a novel form of therapy to enhance myocardial salvage after successful reperfusion. The mechanism appears to be due to stimulation and subsequent "deactivation" of neutrophils peripherally, which thereby reduces their cytotoxic potential in the reperfused myocardium. The role of the oxygen-carrying ability of the perfluorocarbons in the reduction of reperfusion injury remains to be determined. In a pilot study in human beings, Fluosol that was used as adjunctive therapy with angioplasty has also been shown to improve regional ventricular function. Clinical trials with perfluorochemical emulsions appear warranted to determine the role of reperfusion injury in limiting myocardial salvage in patients who are undergoing pharmacologic or mechanical reperfusion.

Animals↗
PubMed1992

The effects of intravenous infusions of selective adenosine A1-receptor and A2-receptor agonists on myocardial reperfusion injury.

To determine the efficacy of very low doses of adenosine on myocardial reperfusion injury and whether its effect is receptor mediated, 78 rabbits underwent 30 minutes of left circumflex artery occlusion and 48 hours of reperfusion. Animals were randomly assigned to receive one of three doses of adenosine, cyclopentyladenosine (a selective A1-receptor agonist), or CGS 21680C (a selective A2-receptor agonist). The drugs were infused for 65 minutes beginning 5 minutes before reperfusion. A significant reduction in histologically determined infarct size was noted with all three doses of adenosine, intermediate and low doses of the A1-receptor agonist (cyclopentyladenosine), and high and intermediate doses of the A2-receptor agonist (CGS 21680C). Furthermore, all three adenosine receptor agonists afforded similar degrees of protection. Results of this study demonstrate that intravenous infusions of very low doses of adenosine significantly enhance myocardial salvage and this protection is receptor mediated. Furthermore, the administration of the A1-receptor agonist would be clinically appealing, since it would avoid the potential side effects associated with activation of A2 receptors.

Adenosine↗
PubMed1992

Pharmacologic perturbation of neutrophils by Fluosol results in a sustained reduction in infarct size in the canine model of reperfusion.

Previous studies have demonstrated that intravenous administration of large doses of Fluosol, a perfluorochemical preparation, reduced infarct size 24 h after reperfusion, an effect that was associated with reduced neutrophil infiltration. The effect of a clinically tolerable dose of Fluosol on infarct size after a prolonged period of reperfusion and its mechanism of action on neutrophils remain unknown. Twenty-one anesthesized closed chest dogs were subjected to 90 min of proximal left anterior descending coronary artery occlusion and 72 h of reperfusion. An additional five dogs that did not undergo regional myocardial ischemia were utilized to explore the mechanism of action of Fluosol on neutrophil function. In the infarct study, animals were randomized to receive either intravenous Fluosol (n = 10) or an equivalent volume of Ringer's lactate solution (control; n = 11) at 15 ml/kg body weight during the last 30 min of occlusion and for the 1st 30 min of reperfusion. Fluosol significantly reduced infarct size when expressed as percent area at risk 72 h after reperfusion (13.7 +/- 2.7% vs. 38.3 +/- 4.5%, respectively, p less than 0.001). This reduction was associated with significant improvement in regional wall motion (18.4 +/- 2.3% vs. 5.5 +/- 2%, p less than 0.001). Endocardial blood flow in the ischemic bed was significantly higher 3 h after reperfusion in Fluosol-treated dogs (0.63 +/- 0.08 vs. 0.34 +/- 0.07 ml/min per g, p = 0.01). Reduced capillary plugging by neutrophils with relative preservation of endothelial cell structure was observed in Fluosol-treated animals. Infusion of Fluosol produced a marked transient decrease in peripheral neutrophil and platelet counts in both ischemic and nonischemic dogs and was associated with a significant reduction in total hemolytic complement levels. Studies of neutrophil function ex vivo revealed a reduction in chemotaxis and lysozyme degranulation after infusion of Fluosol. In vitro experiments showed that Fluosol produced a rapid and sustained activation of neutrophils determined by superoxide anion production. These data demonstrate that low dose intravenous Fluosol produces a sustained reduction in infarct size in the canine model. The beneficial effect may be in part due to the suppression of various neutrophil functions in the reperfused myocardium subsequent to peripheral activation by Fluosol. Such interventions may offer a novel therapy to enhance myocardial salvage by sequestration of circulating neutrophils during the critical early reperfusion period.

Animals↗
PubMed1992

Phagocytic activation of human neutrophils by the detergent component of fluosol.

Fluosol (Alpha Therapeutic Corporation, Los Angeles, CA) an emulsion of perfluorocarbons with a high oxygen-carrying capacity, was approved as an adjunct to alleviate myocardial ischemia during coronary angioplasty. This drug also significantly enhances myocardial salvage presumably related to an action on the neutrophil. The mechanism by which fluosol and its individual components, including the detergent Pluronic F-68, affected neutrophil function was examined. During the incubation of neutrophils with fluosol, a rapid stimulation of superoxide anion production and degranulation which progressively increased over a 30-minute period was detected. Neutrophils incubated with only Pluronic F-68 produced similar amounts of superoxide anion. Cytochalasin B, an inhibitor of phagocytosis, significantly inhibited this superoxide anion generation. As shown previously, neutrophils incubated with fluosol for 30 minutes and then subsequently stimulated manifested a reduction in lysozyme release as compared with untreated cells. Results of an electron microscopic examination confirmed the cellular uptake of the fluosol within phagocytic vacuoles. Neutrophil viability determined by trypan blue was unaffected after fluosol treatment. These observations show that the fluosol emulsion, primarily through micelles formed by the detergent Pluronic F-68, activates human neutrophils by serving as a phagocytic stimulus, which produces a cell refractory to subsequent stimulation.

Blood Substitutes↗
PubMed1991

Role of adenosine in the treatment of myocardial stunning.

Adenosine is an endogenous nucleoside produced from the breakdown of adenosine triphosphate (ATP) that possesses a number of complex cellular and metabolic effects that could ameliorate postischemic contractile dysfunction (myocardial stunning). Potential mechanisms include the repletion of high-energy phosphate stores, reduced myocardial oxygen consumption, a decrease in oxygen-derived free radicals, restoration of calcium homeostasis, and an increase in regional myocardial blood flow. Experimental studies have shown that adenosine can reduce myocardial stunning with or without a concomitant increase in the total myocardial ATP stores. Adenosine may be a useful pharmacologic strategy in the prevention and treatment of ventricular dysfunction following episodes of regional or global ischemia, although further studies are needed to clarify the precise cellular mechanisms involved.

Adenosine↗
PubMed1991

Myocardial reperfusion injury in the canine model after 40 minutes of ischemia: effect of intracoronary adenosine.

To explore the contribution of reperfusion injury to final infarct size after a short duration of ischemia, closed-chest dogs underwent 40 minutes of proximal left anterior descending artery occlusion followed by 3 days of reperfusion. Animals randomly received intracoronary adenosine (n = 8) at 3.75 mg/min during the first hour of reperfusion or no therapy (control, n = 9). Infarct size was measured histologically. Regional ventricular function was determined with contrast ventriculography. The risk region was similar and collateral blood flow in the inner two thirds of the ischemic zone was markedly reduced in both groups (adenosine: 0.05 +/- 0.07 ml/min/gm; control: 0.02 +/- 0.07 ml/min/gm; p = NS). Infarct size as a percent of the area at risk was significantly reduced in the adenosine group (5.0 +/- 1.3% versus 13.5 +/- 3.2%; p = 0.03), associated with a trend for improved recovery of regional ventricular function. Relative endothelial preservation was seen in the adenosine group. These results suggest that reperfusion injury contributes to final myocardial cell necrosis in the closed-chest canine model subjected to 40 minutes of regional ischemia.

Adenosine↗
PubMed1991

Effect of intravenous adenosine on myocardial reperfusion injury in a model with low myocardial collateral blood flow.

The purpose of this study was to investigate the effects of various doses of adenosine administered intravenously on myocardial reperfusion injury in a model with poor collateral blood flow. New Zealand White rabbits were subjected to 30 minutes of occlusion of the obtuse marginal branch of the left circumflex artery and to 48 hours of reperfusion. Animals were randomized to receive intravenous adenosine in doses of 0.1 mg/min (low), 0.3 mg/min (intermediate), or 0.55 mg/min (high), or an equivalent volume of saline (control) commencing 5 minutes prior to reperfusion and continuing through the first 60 minutes of reperfusion. The area at risk was determined in vivo with Monastral blue dye and the area of necrosis was histologically examined with Masson's trichrome stain. Both the intermediate and high doses of adenosine, but not the low dose, significantly (p less than 0.05) decreased mean blood pressure. However, all three doses of adenosine produced a significant (p less than 0.05) and comparable decrease in infarct size expressed as a percent of area at risk (control, 52.0 +/- 4.6%; low, 35.3 +/- 4.1%; intermediate, 31.7 +/- 4.6%; high, 31.3 +/- 4.6%). Regional myocardial blood flow was significantly increased and coronary vascular resistance decreased by all three doses of adenosine in a subset of animals that did not undergo coronary occlusion (p less than 0.05). This study demonstrates that intravenous administration of nonhypotensive doses of adenosine given during the early reperfusion period attenuates reperfusion injury in a model with poor collateral blood flow.

Adenosine↗
PubMed1991

Demonstration of myocardial reperfusion injury in humans: results of a pilot study utilizing acute coronary angioplasty with perfluorochemical in anterior myocardial infarction.

Reperfusion may limit the amount of potentially salvageable myocardium through the introduction of cellular elements into previously ischemic but viable myocardium (reperfusion injury). It has been demonstrated that intracoronary infusion of a 20% intravascular perfluorochemical emulsion (Fluosol) significantly reduces infarct size and results in improved left ventricular function in the canine model. This pilot study was performed to explore the existence of myocardial reperfusion injury in humans. Utilizing Fluosol as a probe in conjunction with emergency coronary angioplasty, 26 patients presenting within 4 h with a first anterior myocardial infarction were randomized to emergency angioplasty or angioplasty followed by a 30-min intracoronary infusion of Fluosol at 40 ml/min. Global and regional ventricular function were assessed immediately and a mean of 12 days after successful angioplasty with contrast ventriculography. Infarct size was semiquantitated with thallium-201 single-photon emission computed tomography (SPECT) images before discharge. Twelve patients (six undergoing angioplasty alone, six treated with angioplasty and Fluosol) had an occluded infarct-related vessel (Thrombolysis in Myocardial Infarction [TIMI] grade 0 to 1) at the time of emergency catheterization and were included in the final analysis. At 12 days after successful angioplasty, the improvement in regional ventricular function was greater in patients receiving adjunctive therapy with intracoronary Fluosol versus those undergoing angioplasty alone utilizing both the radial shortening and centerline method, respectively (23 +/- 3.1% vs. 8 +/- 2.3%, p less than 0.02; and -1.6 +/- 0.4 vs. -2.9 +/- 0.2 SD/chord, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty, Balloon, Coronary↗