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(Circulation. 1996;94:1927-1933.)
© 1996 American Heart Association, Inc.

Articles

Reduction in Myocardial Infarct Size by Basic Fibroblast Growth Factor After Temporary Coronary Occlusion in a Canine Model

Mark C.G. Horrigan, MBBS; Andrew I. MacIsaac, MD; Francesca A. Nicolini, MD, PhD; D. Geoffrey Vince, PhD; Philmo Lee, BS; Stephen G. Ellis, MD; Eric J. Topol, MD

the Experimental Thrombosis Laboratory, Joseph J. Jacobs Center for Thrombosis and Vascular Biology, Department of Cardiology, and Department of Biomedical Engineering (D.G.V.), The Cleveland Clinic Foundation, Cleveland, Ohio.

Correspondence to Eric J. Topol, MD, Department of Cardiology (F-25), The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195. E-mail topole@cesmtp.ccf.org.

	Abstract

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Background Basic fibroblast growth factor (bFGF) has been shown to reduce infarct size in canine acute myocardial infarction; however, the mechanism of tissue salvage remains uncertain. We evaluated the effect of bFGF on infarct size in a model of acute infarction in which coronary occlusion was followed by prolonged reperfusion and sought to determine whether reperfusion attenuates the stimulus for myocardial neovascularization.

Methods and Results Anesthetized dogs undergoing 4-hour balloon occlusion of the left anterior descending coronary artery were treated with intracoronary bFGF (n=8) or vehicle (n=6). Ten-microgram doses of bFGF were administered 10 minutes after occlusion and again immediately before reperfusion. Left ventriculograms were obtained before occlusion, after reperfusion, and preceding euthanasia on day 7. Infarct size, expressed as a percentage of the area at risk, was reduced in bFGF-treated dogs (13.7±2.1% versus 28±3.4%; P=.002). Changes in left ventricular ejection fraction, capillary density, and cellular proliferation—assessed immunohistochemically with factor VIII and proliferating cell nuclear antigen antibodies—were similar in both groups. To assess coronary vasomotor responses to bFGF, a separate hemodynamic study was performed in five anesthetized nonischemic dogs in which incremental bFGF doses up to 100 µg induced no vasodilator response.

Conclusions Treatment with bFGF was associated with a reduction in infarct size without hemodynamic effects or evidence of neovascularization. These data suggest that bFGF mediates myocardial salvage independently of angiogenesis and that reperfusion after infarction may attenuate the stimulus for neovascularization.

Key Words: growth substances • myocardial infarction • vessels • vasodilation

	Introduction

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The extent of myocardial injury and necrosis resulting from an ischemic insult is determined by the duration of interruption to antegrade flow, the size of the compromised territory, and the extent of collateral circulation to the region.^{1 2} In the past decade, developments in the treatment of myocardial ischemia have primarily centered on strategies for restoring impaired antegrade perfusion. Recently, bFGF has been shown to protect ischemic myocardium in association with enhanced collateral development in regions of impaired perfusion.^{3 4 5} In view of the beneficial effects on myocardial viability and contractile function demonstrated in collateralized patients with occlusive coronary artery disease,^{6 7} these findings provide a rationale for investigation of new strategies that use growth factors such as bFGF to pharmacologically enhance collateral growth and to blunt the effects of impaired antegrade myocardial perfusion.

bFGF is an 18-kD heparin-binding polypeptide secreted by several cell types, including vascular endothelial cells,⁸ smooth muscle cells,⁹ and macrophages,¹⁰ and widely distributed in a variety of tissues.¹¹ The molecule has a cell surface receptor linked by a transmembrane domain to an intracellular tyrosine kinase; it binds to heparin, basement membrane, and heparan sulfate components of the extracellular matrix, providing a tissue depot of bFGF.^{12 13} Endothelial cells are stimulated by bFGF to proliferate, migrate, and form capillary-like tubular structures in cell cultures, in which bFGF also prolongs cell survival times.^{14 15} Embryonic and mature cardiac myocytes contain bFGF^{16 17} ; however, although embryonic myocytes are capable of proliferating in the process of cardiogenesis, mature cardiac myocytes are terminally differentiated, and the role of bFGF in the mature heart remains undefined.

In the setting of chronic ischemia, bFGF has been shown to increase capillary density and blood flow via newly formed collaterals.⁴ In a similar model, collateral flow alone was shown to support normal contractile function.¹⁸ It has been reported that bFGF possesses coronary⁴ and systemic^{3 19} vasodilator properties, raising the possibility that myocardial flow may also be increased by opening or increasing conductance in preexisting collateral channels.

In a canine model of acute infarction with permanent coronary occlusion, Yanagisawa-Miwa and coworkers⁵ demonstrated that bFGF reduced infarct size and that this reduction was associated with an increase in myocardial capillary density 1 week after infarction. Even with convincing evidence of angiogenesis in tissue that has been subjected to an acute ischemic insult, it is difficult to envisage angiogenesis as the principal mechanism of tissue salvage occurring within the time frame of myocardial necrosis. The aims of the present investigation were (1) to evaluate the effect of bFGF on infarct size in a canine model in which acute occlusion was followed by reperfusion and (2) to determine whether angiogenesis would occur in this setting or whether restoration of antegrade flow would act to attenuate or abolish the stimulus for neovascularization.

	Methods

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Coronary Occlusion and Reperfusion
Twenty-two mongrel dogs of either sex (weight, 17 to 23 kg) were randomly assigned to treatment with bFGF or vehicle. After the animals received anesthesia with sodium pentobarbital (25 mg/kg IV), intubation, and ventilation with room air, the right carotid artery was exposed, ligated distally, and cannulated. Aortic blood pressure, heart rate, and ECG were monitored continuously throughout the procedure. After baseline left ventriculography was accomplished via a 6F pigtail catheter, selective left coronary angiography was performed via an 8F angioplasty guiding catheter. Because of the potential interaction between heparin and bFGF, intraprocedural anticoagulation was achieved with the use of Hirulog, a synthetic direct thrombin inhibitor²⁰ ; after an intravenous loading dose of 2.5 mg/kg, intravenous infusion was commenced at 5 mg·kg^-1·h^-1 and the rate adjusted to maintain the activated clotting time at >300 seconds.

An angioplasty balloon catheter (balloon:artery ratio 1.0) was then inflated at 2 atm in the middle part of the LAD distal to the first diagonal branch, and occlusion was confirmed angiographically. After 4 hours' occlusion, the balloon catheter was deflated and removed, and LAD patency was confirmed angiographically. Ten micrograms of human recombinant bFGF (in 20 mmol/L sodium citrate, 1 mmol/L EDTA, and 9% sucrose, pH 5; Scios Nova Inc) in 10 mL normal saline or vehicle (10 mL normal saline) was administered directly into the left main coronary artery via the guiding catheter 10 minutes after occlusion and again just before reperfusion. After reperfusion, left ventriculography was repeated. All surgical procedures were performed with the use of a sterile technique. Seven days after the first procedure, dogs were anesthetized, intubated, and ventilated in the same manner as before. Patency was confirmed angiographically, left ventriculography was repeated, and euthanasia was performed with a lethal dose of pentobarbital.

Measurement of Activated Clotting Time
Activated clotting time was measured with the use of the Hemochron 801 timer (International Technidyne Corp). After 2 mL of whole blood was collected into a Hemochron tube containing 12 mg of Johns-Manville diatomaceous earth, the time taken to complete coagulation at 37°C was measured.

Delivery and Biological Activity of bFGF
To ensure delivery of bFGF after passage through the manifold and angioplasty guiding catheter, radiolabeled bFGF was passed through new and used systems. To simulate the conditions of an in vivo experiment, 20 µg of cold bFGF was mixed with 25 µCi of radiolabeled bFGF in 20 mL of normal saline solution. A second batch of 20 µg of cold bFGF was mixed with 25 µCi of radiolabeled bFGF in 20 mL of normal saline solution containing 1 mg/mL of dog albumin (Sigma Chemical Co). The number of counts per minute from both solutions was quantified in a scintillation counter. Ten-milliliter aliquots of the radiolabeled solutions were then delivered through used and new guiding catheters and manifolds and flushed with an additional 10 mL of normal saline. The number of counts per minute in the solutions collected after passage through the catheter system was measured. The difference in counts per minute between the incoming and outgoing solution was used as an index of bFGF loss within the delivery system. Under the conditions described above, there was minimal loss of activity in the delivery system (Table 1). The bFGF used in the experiments was compared in a mitogen assay with human recombinant bFGF from a commercial source (Boehringer Mannheim) that had proven activity in previous assays.²¹ The potency of both lots of bFGF was similar, as assessed by ³H-thymidine uptake after stimulation of cultured human fibroblasts (data not shown).

View this table: [in this window] [in a new window]   Table 1. Delivery of Radiolabeled bFGF in Normal Saline and Albumin Solutions Through Used and New Guiding Catheters and Manifolds

Determination of Infarct Size
After euthanasia and rapid excision of the heart, the LAD and circumflex arteries were cannulated individually. Simultaneously, at a pressure of 100 mm Hg, the circumflex vessel was perfused with Evans blue dye and the LAD with triphenyltetrazolium chloride for 10 minutes. Hearts were then fixed by perfusion with HistoChoice (Ameresco) for 4 hours, after which the left ventricle was cut into 1-cm-thick slices perpendicular to its long axis, and the slices were weighed. With this technique, areas of viable tissue in the LAD distribution are stained red, necrotic areas remain white, and the circumflex territory is stained blue. For each slice, the area at risk, the area of infarction, and the circumflex territory were determined by computer-assisted planimetry, as previously described.²²

Histology and Immunohistochemistry
Multiple tissue samples were taken from areas of infarction and areas at risk of infarction for histological examination to seek evidence of neovascularization. Given the assumptions that (1) neovascularization of ischemic regions would proceed from the circumflex and nonoccluded LAD distributions and (2) the tissue stimulus for neovascularization would be intense in tissue adjacent to the infarct zone, "border-zone" samples were taken from the area at risk midway between the edges of the macroscopically infarcted myocardium and the junction of the LAD and circumflex territories. Staining with hematoxylin and eosin was used to confirm the presence of tissue necrosis in the infarct zones. Immunohistochemical staining of tissue samples was performed with factor VIII–related antigen to detect endothelial cells and PCNA to detect proliferating cells²³ (Figs 1 and 2).

View larger version (148K): [in this window] [in a new window]   Figure 1. Photomicrograph of canine myocardial tissue from an infarct-adjacent region stained for factor VIII. Vascular structures are clearly identified by brown staining of endothelial cells. (Magnification x40.)

View larger version (129K): [in this window] [in a new window]   Figure 2. Photomicrograph of canine myocardial tissue from an infarct-adjacent region stained for PCNA. Proliferating endothelial cells stain brown and are clearly visible within the vascular wall. (Magnification x400.)

After being embedded in paraffin, 5-µm sections were cut and collected onto glass slides coated with 1% polychloroprene in xylene. After being dried for 60 minutes at 60°C, paraffin was removed in three changes of xylene. The tissue was then rehydrated through graded alcohols before being rinsed in PBS. Immunohistochemical staining was performed in a Jung Histostainer (Leica). A 0.6% hydrogen peroxide solution in PBS was then applied for 5 minutes to remove any endogenous peroxidase. For the PCNA sections, a blocking solution of 1:10 (vol/vol) normal rabbit serum (Dako Corp) was added for 10 minutes before application of a 1-in-50 dilution of murine monoclonal antibodies directed against PCNA (PC10 Clone, Dako Corp). For the factor VIII–related antigen stain, a blocking solution of 1:10 (vol/vol) normal swine serum (Dako Corp) was added for 10 minutes before application of a 1:300 dilution of rabbit polyclonal antibodies directed against factor VIII–related antigen (Dako Corp). The dilutions of the primary antibodies were prepared with the use of 1% BSA in PBS and were incubated with the tissue sample at 30°C for 60 minutes. A 1:200 dilution of biotinylated rabbit anti-mouse polyclonal antibody (Dako Corp) was then added for 30 minutes to the PCNA sections, and 1:200 biotinylated swine anti-rabbit polyclonal antibody (Dako Corp) was added to the factor VIII–stained sections for 30 minutes. These antibodies were labeled with an Elite streptavidin-biotin-peroxidase complex (Vector Laboratories) applied for 30 minutes. The final stage involved the addition of 3,3'-diaminobenzidine (Vector Laboratories) as a chromogen. Between steps, the sections were rinsed for 2 minutes in PBS. Slides were then rinsed in distilled water, dehydrated, cleared in xylene, and mounted in Permount (Fisher Scientific). In each staining preparation, sections treated with 1% BSA in PBS instead of with the primary antibody were included as negative controls, and sections of human tonsil were used as positive controls.

Cell Counts
Photographs of immunohistochemically stained tissue sections were taken without knowledge of treatment assignment. After low-power examination, five to seven representative fields (0.5x0.34 mm) were photographed from each section at a magnification of 200x. Whenever possible, consecutive adjacent fields were photographed. In sections from the infarct zone, fields with relative preservation of tissue architecture were selected, obviating spurious increases in vessel density due to preservation of vascular structures in areas of parenchymal loss and stromal collapse. Cells that stained positive for PCNA and factor VIII (regardless of the presence of a vascular lumen) were counted by two independent observers blinded to treatment assignment (interobserver correlation coefficient, r=.69; P<.0001). Immunostaining for factor VIII and PCNA represented the techniques currently used as diagnostic tools for measurement of tumor angiogenesis.^{24 25 26}

Left Ventricular Ejection Fraction
Left ventricular ejection fractions were determined from single-plane left ventriculograms measured by a trained technician who was blinded to treatment assignment. Ejection fractions were calculated by use of the length-area method²⁷ with a computer analysis package (Angiographic Ventricular Dynamics 5.1, Siemens).

Acute Hemodynamic Studies
In five additional dogs of either sex (weight, 19 to 22 kg), we compared the effects of intracoronary bFGF on coronary hemodynamic parameters with those of temporary coronary occlusion and intracoronary NTG. The studies were performed with the use of a standard open-chest model²⁸ in which the LAD was isolated and instrumented with a Doppler flow probe to measure blood flow (Crystal Biotech). A 2F catheter was advanced retrogradely via a small proximal branch of the LAD into the left main vessel for administration of drugs. Blood flow responses after 10- and 20-second periods of LAD occlusion and after incremental doses of intracoronary NTG (1, 10, and 100 µg) were recorded to confirm the presence of coronary vascular reactivity. Incremental doses of intracoronary bFGF (1, 10, and 100 µg) were then given, and coronary flow responses were measured. bFGF (buffered as described above) and NTG solutions were prepared in 1 mL of normal saline just before administration and were given as boluses over 20 seconds. Blood pressure, heart rate, and ECG were monitored continuously throughout the procedure. Coronary vascular resistance (CVR) was calculated according to the formula

Institutional Approval and Sample Size
The protocol was approved by the Cleveland Clinic Foundation Institutional Review Board and Animal Research Committee. Animals were handled in accordance with the National Institutes of Health guidelines for the use of experimental animals. In the occlusion-reperfusion study, 22 dogs were randomized to receive bFGF or vehicle. Five dogs (2 treated with bFGF, 3 with vehicle) died of arrhythmias before completion of the protocol. Three dogs (1 treated with bFGF, 2 with vehicle) were excluded because of persistent occlusion at the site of balloon occlusion. No dogs were excluded from the acute hemodynamic study.

Data Analysis
All data are expressed as mean±SEM. Differences between groups were evaluated by use of two-tailed, unpaired t tests. The Pearson correlation coefficient was used to assess interobserver variability for cell counts. Repeated measurements of left ventricular ejection fraction were compared by use of two-way ANOVA. Differences were considered significant at a value of P<.05.

	Results

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Occlusion-Reperfusion Study
Blood pressure and heart rate were similar in both groups throughout the experiment (Table 2). Heart rate was increased during reperfusion in vehicle- and in bFGF-treated dogs (both P=.043 versus baseline) because of nonsustained ventricular tachycardia and frequent ventricular ectopic activity. No systemic hemodynamic changes were noted after bFGF was administered. The areas at risk were similar in both groups (41±8 cm² versus 40±6 cm², vehicle versus bFGF). In the bFGF-treated group, infarct size expressed as a percentage of the area at risk was 13.7±2.1%, which was significantly less than in dogs receiving vehicle (28.4±3.4%; P=.002; Fig 3). At baseline, left ventricular ejection fractions were similar in both groups (bFGF versus vehicle, 42.6±1.9% versus 44.8±3.5%). After reperfusion (bFGF versus vehicle, 33.1±5.4% versus 40.3±3.2%) and again at 1 week after infarction (bFGF versus vehicle, 33.6±3.6% versus 38.8±3.5%), ejection fractions showed no significant difference between groups (Fig 4).

View this table: [in this window] [in a new window]   Table 2. Effects of Vehicle and bFGF on Heart Rate and Mean Arterial Pressure at Baseline, During Occlusion, During Reperfusion, and on Day 7

View larger version (10K): [in this window] [in a new window]   Figure 3. Effects of vehicle and bFGF on myocardial infarct size after temporary coronary occlusion. Infarct size, measured on day 7, is expressed as a percentage of the area at risk.

View larger version (18K): [in this window] [in a new window]   Figure 4. Serial angiographic left ventricular ejection fractions in dogs treated with vehicle or bFGF. Measurements were made before LAD occlusion, after reperfusion, and on day 7. Two-way ANOVA showed no differences within or between groups.

Microscopic examination of sections demonstrated concordance between triphenyltetrazolium chloride infarct delineation and histological features of myocardial necrosis. Although bFGF treatment was associated with significant myocardial salvage, there was no difference in the number of endothelial cells per high-power field within the infarcted region (bFGF versus vehicle, 241±16 versus 221±18 cells/hpf; P=.8) or in the number of endothelial cells in the border zones (bFGF versus vehicle, 247±18 versus 245±15 cells/hpf; P=.63). Because of the potential for spurious PCNA counts in areas of leukocyte infiltration, PCNA counts were obtained from border zones only; these counts were similar in both groups (bFGF versus vehicle, 10.1±2.3 versus 7.3±2.3 cells/hpf; P=.4).

Acute Hemodynamic Studies
The results of the occlusion-reperfusion study demonstrated a reduction in infarct size without histochemical evidence of myocardial neovascularization. The acute hemodynamic study was performed to assess the presence of a vasodilator action of bFGF as described in dogs and other species^{3 4 19} whereby flow to the infarct zone could possibly be augmented by an increase in the conductance of preexisting collateral channels, independently of neovascularization. In the five dogs studied, coronary blood flow and coronary vascular resistance were unchanged after incremental pharmacological doses of intracoronary bFGF despite pronounced vasodilator responses to 10- and 20-second coronary occlusion and intracoronary NTG (Table 3). In addition, three of the dogs were monitored for 30 minutes after the final dose of bFGF (100 µg) to detect the presence of a delayed vasodilator response as reported previously.⁴ No significant hemodynamic changes were observed in response to bFGF during the experiment.

View this table: [in this window] [in a new window]   Table 3. Acute Hemodynamic Findings After Administration of bFGF Into the LAD in Dogs

	Discussion

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In the present study, we demonstrated that treatment with bFGF was associated with a significant reduction in infarct size 1 week after infarction. This reduction in infarct size was not associated with any difference in intraprocedural hemodynamic parameters, and there was no immunohistochemical evidence of increased tissue vascularity or cellular proliferation. Thus, in the absence of persistent coronary occlusion, we observed a significant reduction in infarct size without evidence of myocardial neovascularization.

Under these conditions, theoretical mechanisms to account for myocardial salvage after administration of bFGF would include the following: (1) augmentation of collateral flow to the infarct zone by growth of new vessels; (2) an increase in collateral flow by dilation of preexisting collateral channels; and (3) a protective effect of bFGF on ischemic myocytes.

For several reasons, it is difficult to postulate that angiogenesis was the principal mechanism of myocardial salvage in this model. In dogs, >75% of the tissue in the infarct zone is irreversibly damaged within 4 hours of coronary occlusion, and after initial increases, collateral flow stimulated by ischemia does not increase further until 6 hours after the onset of ischemia.²⁹ Although endothelial DNA synthesis occurs rapidly in response to bFGF,³⁰ budding angiogenesis in vitro, stimulated by pharmacological doses of bFGF, requires 2 to 3 days,^{14 31} and even in preformed coronary collateral vessels in vivo, completion of the first endothelial cell division requires 22 hours from the onset of ischemia.^{32 33} Thus, within the relatively brief window when tissue injury is reversible, it is difficult to understand how the angiogenic process could be activated with growth of new vessels capable of achieving tissue salvage in an area of severe metabolic stress.

The demonstration of myocardial salvage without evidence of angiogenesis led us to investigate the potential of bFGF to maximize collateral flow by dilating preexisting collateral channels. Collateral vessels have been shown to have a normal pattern of vasomotor reactivity,³⁴ and it is likely that increased conductance might reduce ischemia in the ischemic penumbra of the infarct zone. Although the dogs in the acute hemodynamic study showed normal coronary flow reserve, with increases in coronary flow of >300% and 130% in response to 20-second coronary occlusion and NTG, respectively, in contrast to previous reports,^{4 19} we did not observe hemodynamic changes consistent with a significant vasodilator effect subsequent to intracoronary administration of bFGF.

Although there is little doubt that angiogenesis has a major role in bFGF-mediated protection of chronically ischemic myocardium, the mechanism of its protective action in acute infarction is not clearly defined and necessarily involves other mechanisms. Our data confirm that bFGF reduces infarct size, but in the setting of ischemia with reperfusion, myocardial salvage may occur without neovascularization or effects on preexisting vessels. The remaining possibility is that bFGF has a cytoprotective effect on the ischemic cardiac myocyte. In cell cultures, bFGF extends cell viability,¹⁵ and in vivo, it has been shown to prevent the death of injured neurons.³⁵ bFGF has been shown to suppress the spontaneous onset of apoptosis by a tyrosine kinase–dependent mechanism.³⁶ Cardiac myocytes are terminally differentiated, and the rate of apoptosis would be expected to be low. However, this histologically evanescent process may be important in the responses of vessel wall components to injury, and recent development of molecular markers may facilitate assessment of its significance in this setting.^{37 38} Recently, Padua et al³⁹ demonstrated in vitro that bFGF exerts a cardioprotective effect in perfused rats hearts. It is conceivable that the cytoprotective effect we observed in the present study represents the initial and the faster mechanism by which bFGF reduces myocardial damage during ischemia. Subsequently, if ischemia persists, bFGF-induced angiogenesis may assume a more important significance in the determination of myocardial salvage.

Yanagisawa-Miwa et al⁵ observed infarct size reduction with angiogenesis; we also observed reduced infarct size, but without evidence of neovascularization. These results, however, may not be inconsistent. First, the demonstration of myocardial salvage without neovascularization suggests (at least, in the occlusion-reperfusion model) that angiogenesis is not mandatory for salvage when bFGF is given in acute myocardial infarction. Furthermore, it raises the possibility that angiogenesis may be an independent phenomenon, occurring after myocardial necrosis is complete. Second, we hypothesize that restoration of antegrade perfusion may attenuate the stimulus for neovascularization, explaining the difference between our results and those observed in the occlusive model of Yanagisawa-Miwa et al. It is likely that the milieu promoting myocardial angiogenesis, whether mediated chemically, as a result of physical forces, or both, is more protracted in a model in which vessel occlusion remains unrelieved.

There are significant limitations in the extrapolation of findings in a canine model to the human coronary circulation. Humans and pigs have fewer preformed collaterals, tend to develop subendocardial networks rather than the subepicardial anastomoses characteristically seen in the dog, and progress more rapidly to transmural infarction after vascular occlusion.²⁹ Thus, our findings in dogs may not accurately represent responses to bFGF in humans. Furthermore, strict comparison of histochemical indexes of myocardial neovascularization with anatomic measures used by other groups is not possible. Although left ventricular ejection fraction was diminished after reperfusion in both groups and remained at a similar level on day 7, these changes were smaller than anticipated and did not reach statistical significance. Assessment of global function is a less sensitive index of regional function of a modest area of the total left ventricular mass than direct measurement of contractility in the region of interest. However, changes in left ventricular ejection fraction would perhaps be of greater magnitude if the LAD were occluded proximally to the first diagonal branch. With larger infarcts, bFGF treatment might have had a greater impact on global left ventricular function. In addition, the almost universal presence of reperfusion arrhythmias further diminishes accuracy in estimating myocardial contractility. As reported elsewhere,⁴ hemodynamic studies were undertaken in nonischemic dogs. Although pharmacological doses of bFGF were used in the acute hemodynamic study, the possibility that coronary vasodilator responses to bFGF may depend on the presence of ischemia cannot be excluded.

This study has demonstrated that bFGF reduces the extent of infarction in the canine occlusion-reperfusion setting. Although there is little doubt that the beneficial effects of bFGF on coronary perfusion in chronic ischemia are mediated principally by its angiogenic actions, we have demonstrated that myocardial salvage occurs independently of neovascularization after administration of bFGF in the setting of acute myocardial infarction. Further evaluation of coronary vasomotor responses to bFGF in ischemic and nonischemic settings and investigation of the potential cytoprotective properties of bFGF in acute ischemia promise to provide fertile and clinically relevant areas for future investigation.

	Selected Abbreviations and Acronyms

 

bFGF = basic fibroblast growth factor cells/hpf = cells per high-power field LAD = left anterior descending coronary artery NTG = nitroglycerin PCNA = proliferating cell nuclear antigen

	Acknowledgments

 
This study was supported in part by a grant from Cardiovascular Therapeutics, Mountain View, Calif. The authors wish to thank Earl Poptic, BS, for assistance with the bFGF catheter-delivery study and mitogen assays, Dr Jonathan Myles for reviewing the histology data, and Christine Kassuba for editorial assistance.

Received March 27, 1996; revision received May 22, 1996; accepted June 7, 1996.

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