Cytomegalovirus infection of rats increases the neointimal response to vascular injury without consistent evidence of direct infection of the vascular wall.

BACKGROUND: Previous studies suggest that infection may play a role in restenosis and atherogenesis; cytomegalovirus (CMV) is one of the implicated pathogens. To determine a potential causal role of CMV in these disease processes, we assessed whether CMV infection increases the neointimal response to injury of the rat carotid artery. METHODS AND RESULTS: Carotid injury was performed on 60 rats; immediately thereafter, 30 rats were infected with rat CMV, and the other 30 were mock-infected. Six weeks later, rats were euthanized, and the salivary glands, spleen, and carotid arteries were harvested. CMV infection was associated with significant exacerbation of the neointimal response to injury (neointimal to medial ratio 0.81+/-0. 59 versus 0.31+/-0.38 in CMV-infected versus control rats; P<0.0001). This occurred despite absence of infectious virus from vascular tissues and detection of CMV DNA by polymerase chain reaction in the injured artery only at day 3 after infection. Persistent distant infection, associated with systemic cytokine response, was evidenced by isolation of infectious virus from homogenates of both salivary glands and spleen and by higher serum levels of interleukin (IL)-2 and IL-4 (but not interferon-gamma and tumor necrosis factor-alpha) in infected versus noninfected rats. CONCLUSIONS: CMV infection of immunocompetent adult rats increases the neointimal response to vascular injury, suggesting that CMV may play a causal role in atherosclerosis/restenosis. Importantly, this CMV-induced response occurs even without the presence of virus in the vascular wall, suggesting that inflammatory and immune responses to infection of nonvascular tissues may contribute to the vascular response to injury.

The basis of molecular strategies for treating coronary restenosis after angioplasty.

Excessive smooth muscle cell proliferation significantly contributes to restenosis, which occurs in 25% to 50% of patients within 6 months of coronary angioplasty. Because successful treatment will probably depend on our acquiring a comprehensive knowledge of the molecular and cellular mechanisms involved, this report reviews 1) information relevant to the molecular and cellular mechanisms responsible for the smooth muscle cell(s) response to vascular injury, and 2) several molecular-based therapeutic strategies currently being explored as possible approaches to the control of restenosis, including recombinant DNA technology to target delivery of cytotoxic molecules to proliferating smooth muscle cell(s), antisense strategies to inhibit expression of gene products necessary for cell proliferation and gene therapy.

Investigation of the mechanism of chest pain in patients with angiographically normal coronary arteries using transesophageal dobutamine stress echocardiography.

OBJECTIVES: The present study sought to determine whether myocardial contractile abnormalities accompany the development of chest pain in patients with normal coronary angiograms. BACKGROUND: The mechanism of chest pain in patients with angina despite a normal coronary arteriogram is controversial. Although previous studies postulated the existence of coronary microvascular dysfunction, others failed to find evidence of myocardial ischemia, and recent studies have demonstrated abnormal cardiac sensitivity in these patients that can lead to chest pain on a nonischemic basis. METHODS: Seventy patients (26 men and 44 women, mean age 49 +/- 10 years) with angina-like chest pain and angiographically normal coronary arteries underwent exercise treadmill testing, radionuclide angiography at rest and during exercise, thallium stress testing and transesophageal dobutamine stress echocardiography. The results of exercise treadmill testing and stress echocardiography were compared with those obtained in 26 normal control subjects (19 men and 7 women, mean age 56 +/- 7 years). RESULTS: Abnormalities consistent with myocardial ischemia were noted in 31% of the patients during exercise treadmill testing, in 16% during exercise radionuclide angiography and in 18% during thallium stress testing. The findings of the radionuclide studies were not concordant with one another and were not related to the presence of repolarization changes during exercise testing. During infusion of dobutamine, chest pain developed in 59 patients (84%) and in none of the control subjects (p < 0.0001); repolarization changes occurred in 22 patients (34%) and in 2 control subjects (8%) (p < 0.04). None of the patients or the control subjects developed regional wall motion abnormalities with dobutamine. The quantitative myocardial contractile response to dobutamine was similar in patients and control subjects, with an 80% power to detect a 25% difference in systolic wall thickening at the maximal dose of dobutamine. CONCLUSIONS: There was no agreement in the results of noninvasive tests in our patients. Despite the frequent provocation of chest pain and electrocardiographic abnormalities with dobutamine, the patients demonstrated a quantitatively normal myocardial contractile response without development of wall motion abnormalities. These observations strongly suggest that myocardial ischemia is not the cause of chest pain in patients with a normal coronary arteriogram.

Intracoronary basic fibroblast growth factor enhances myocardial collateral perfusion in dogs.

OBJECTIVE: In preparation for clinical trials of basic fibroblast growth factor (bFGF) to treat ischemic heart disease, we sought to identify a clinically feasible method of bFGF administration. BACKGROUND: Basic FGF has been shown to promote collateral development after experimentally induced coronary occlusion; however, methods of bFGF delivery that have been shown to be effective in previous investigations would not be practical for clinical use. METHODS: Four randomized, blinded, controlled investigations were conducted independently and sequentially in an established canine model. For all studies, dogs underwent operative placement of proximal left circumflex coronary artery ameroid constrictors. The four investigational regimens included: 1) bFGF by central venous bolus injection, 1,740 microg/day for one, two or seven days; 2) bFGF by intravenous infusion, 100 microg/kg body weight per day for seven days; 3) bFGF by pericardial instillation, 2,000 microg/day for 7 days; and 4) bFGF by intracoronary injection (Judkin's technique), 100 microg/kg per day for one or two days. Each substudy included a contemporaneous vehicle control group. Collateral perfusion (microspheres) was assessed during maximal coronary vasodilation during the first month after ameroid placement. RESULTS: Maximal collateral perfusion in dogs that received intracoronary bFGF for two days exceeded that of concurrent control dogs by 31% (p < 0.01). Perfusion was not increased in dogs that received single-dose intracoronary bFGF. Basic FGF administration by central venous bolus injection, intravenous infusion and pericardial injection failed to enhance collateral perfusion. CONCLUSIONS: Administration of bFGF by the intracoronary route, an intervention that is feasible in patients, augments collateral development in dogs. These data provide a rationale for clinical testing of intracoronary bFGF in ischemic heart disease.

Basic fibroblast growth factor in patients with intermittent claudication: results of a phase I trial.

OBJECTIVES: This phase I study was designed to evaluate the safety, tolerability and pharmacokinetics of intra-arterial basic fibroblast growth factor (bFGF) in patients with atherosclerotic peripheral arterial disease (PVD) and intermittent claudication. We also assessed the effects of basic fibroblast growth factor (bFGF) on calf blood flow as a measure of biologic activity. BACKGROUND: Preclinical studies have shown that bFGF, an angiogenic peptide, promotes collateral development in animal models of myocardial and hind limb ischemia. The safety and efficacy of bFGF in patients is unknown, and early clinical trials are underway in coronary and peripheral arterial disease. METHODS: A double-blind, placebo-controlled, dose-escalation trial was conducted in patients with claudication demonstrating ankle/brachial index <0.8. Patients were randomly assigned to placebo (n = 6), 10 microg/kg of bFGF (n = 4), 30 microg/kg of bFGF once (n = 5) and 30 microg/kg of bFGF on two consecutive days (n = 4). Study drug was infused into the femoral artery of the ischemic leg. Detailed safety information including retinal photography for neovascularization were obtained through one year. Calf blood flow was measured with strain gauge plethysmography in the two higher dose treatment groups and in four placebo patients at baseline, one month and three to seven months after treatment. RESULTS: Intra-arterial bFGF was safe and well-tolerated. The half-life was 46 +/- 21 min. Calf blood flow increased at one month by 66 +/- 26% (mean +/- SEM) and at six months by 153 +/- 51% in bFGF-treated patients (n = 9, p = 0.002). Flow did not change significantly in the placebo group. CONCLUSIONS: In this initial randomized, double-blind, placebo-controlled trial in patients with atherosclerotic PVD and claudication, bFGF was well-tolerated. The data suggest a salutary biologic effect, and initiation of phase 2 trials is warranted.

Effect of basic fibroblast growth factor on myocardial angiogenesis in dogs with mature collateral vessels.

OBJECTIVES: We sought to evaluate the potential of basic fibroblast growth factor (bFGF) to enhance coronary collateral perfusion in dogs with chronic single-vessel coronary occlusion. A secondary goal was to examine whether the salutary effects of bFGF treatment, previously proved effective in the short term, would be maintained in the long term (6 months). BACKGROUND: bFGF, an angiogenic growth factor, is currently the subject of a Phase I trial in patients with ischemic heart disease. It has been shown to promote collateral development in dogs with progressive coronary occlusion when given during the period of natural collateralization. The effect of bFGF on quiescent collateral vessels, a subject of significant clinical importance, is uncertain. METHODS: Dogs were subjected to ameroid-induced occlusion of the left circumflex coronary artery and randomized to bFGF (1.74 mg/day for 7 days), a regimen previously proved effective, or to saline solution. Maximal collateral perfusion was assessed 6 months later, and the dogs were reassigned to a course of bFGF or saline solution. Collateral perfusion was reevaluated after the second treatment course. RESULTS: At 6 months, collateral function was identical in the groups treated initially with bFGF and saline solution. The subsequent course of bFGF did not induce further collateralization. CONCLUSIONS: Although we previously demonstrated the salutary effects of this bFGF regimen in the short term (5 weeks), collateral flow in control dogs reached parity with that of bFGF-treated dogs after 6 months. bFGF did not induce further collateralization in dogs with mature collateral vessels, underscoring the priming role of ischemia for bFGF-induced collateral development.

Experimental evaluation of coronary collateral development.

During the last decade, there has been great interest in the potential use of biologic agents and mechanical techniques to enhance myocardial collateral development. Available experimental methods to detect the effects of interventions designed to improve collateral function include assessment of vascular cell proliferation, quantification of vessel number and size, appraisal of myocardial perfusion, and evaluation of myocardial function. The purpose of this review is to discuss the various experimental approaches for the evaluation of coronary collateral development, highlighting the relative strengths and limitations of the commonly used animal models and methods of assessment.

A model to assess interventions to improve collateral blood flow: continuous administration of agents into the left coronary artery in dogs.

OBJECTIVE: The aim was to develop an experimental model in which angiogenic growth factor(s) could be targeted locally to enhance myocardial collateral formation. A preparation was developed in which agents could be infused selectively into the left main coronary artery on a chronic basis to assess the potential of acidic fibroblast growth factor (FGF) to improve collateral blood flow. METHODS: Ameroid constrictors were placed on the left circumflex coronary artery of mixed hounds. Five weeks after ameroid placement, the artery was ligated and transected at the point of ameroid occlusion; a catheter was inserted and passed retrogradely into the left main coronary artery. The catheter was connected to an implantable infusion pump that provided continuous intracoronary drug infusion for 4 weeks. Dogs were randomised to receive acidic FGF with heparin (30 micrograms.h-1 and 30 IU.h-1, respectively, n = 16) or heparin alone (30 IU.h-1, n = 14). Regional myocardial blood flow was determined in the conscious state at the beginning and end of treatment. RESULTS: There were no deaths or important surgical complications related to the establishment of the coronary artery infusions. During the treatment interval (5-9 weeks after ameroid placement) the ratio of maximum ischaemic zone/normal zone blood flow increased from 0.39(SD 0.10) to 0.50(0.11) (p < 0.01) in dogs treated with acidic FGF plus heparin; however, similar improvement was noted in dogs treated with heparin alone. Ischaemic zone and normal zone vascular density was also equivalent in the two groups. CONCLUSIONS: This preparation makes possible the chronic intracoronary administration of agents which may promote myocardial angiogenesis, and allows assessment of collateral blood flow before and after treatment. As given in this investigation, acidic FGF had no demonstrable effect on collateral blood flow; however, this model may facilitate the identification of agents that do enhance myocardial collateral formation.

Chronic non-vascular cytomegalovirus infection: effects on the neointimal response to experimental vascular injury.

OBJECTIVE: Epidemiologic and mechanistic evidence implicates a role for cytomegalovirus (CMV) in atherogenesis. Recently, we demonstrated that CMV has the capacity to causally contribute to atherogenesis; acute infection of rats with rat CMV (RCMV) 1 day after carotid artery injury increased neointimal accumulation. Importantly, in the injured vessel infectious virus could not be detected and viral genome was present only transiently, suggesting that additional mechanisms play a role in the virus-induced exacerbation of the vascular injury response other than the changes caused by direct infection of vessel wall cells. The present investigation was designed to determine whether chronic persistent RCMV infection, more relevant to the clinical situation, also exacerbates the response to injury and, if so, whether similar mechanisms are operative. METHODS: Sixty 3-week-old male Spraque-Dawley rats received an i.p. injection of either 10(6) TCID50 RCMV (Priscott strain) or normal saline. The left carotid artery was balloon-injured 3 months after infection. Rats were killed 6 weeks later. This model produces persistent infection, as demonstrated by presence of infectious virus in the salivary glands at time of sacrifice. RESULTS: The neointima to media (N/M) ratio of the injured vessel was 41% greater in the RCMV-infected than in control rats (1.40 +/- 0.48 vs. 0.99 +/- 0.45; P = 0.003). The aorta never contained infectious RCMV, and exhibited RCMV DNA, detected by PCR, only transiently. The persistent infection of non-vascular tissues was associated with increased serum levels of IL-2, IL-4 and IFN-gamma. CONCLUSIONS: CMV infection of young rats causes persistent infection of non-vascular tissues and increased cytokine levels. The neointimal response to subsequent vascular injury is increased, despite absence of virus from the vessel wall. These findings, as in acute infection following vascular injury, suggest that inflammatory and immune responses to chronic persistent CMV infection contribute to an exaggerated response to vascular injury.

Adenoviral-mediated gene transfer induces sustained pericardial VEGF expression in dogs: effect on myocardial angiogenesis.

OBJECTIVE: Angiogenic peptides like VEGF (vascular endothelial growth factor) and bFGF (basic fibroblast growth factor) have entered clinical trials for coronary artery disease. Attempts are being made to devise clinically relevant means of delivery and to effect site-specific delivery of these peptides to the cardiac tissue, in order to limit systemic side-effects. We characterized the response of the pericardium to delivery of a replication-deficient adenovirus carrying the cDNA for AdCMV.VEGF165, and assessed the effect of pericardial VEGF165 on myocardial collateral development in a canine model of progressive coronary occlusion. METHODS: Ameroid constrictors were placed on the proximal left circumflex coronary artery of mongrel dogs. Ten days later, 6 x 10(9) pfu AdCMV.VEGF165 (n = 9). AdRSV.beta-gal (n = 9), or saline (n = 7) were injected through an indwelling pericardial catheter. Transfection efficiency was assessed by X-gal staining. Pericardial and serum VEGF levels were measured serially by ELISA. Maximal myocardial collateral perfusion was quantified with radiolabeled or fluorescent microspheres 28 days after treatment. RESULTS: In AdRSV.beta-gal-treated dogs, there was extensive beta-gal staining in the pericardium and epicardium, with minimal beta-gal staining in the mid-myocardium and endocardium. Pericardial delivery of AdCMV.VEGF165 resulted in sustained (8-14 day) pericardial transgene expression, with VEGF levels peaking 3 days after infection (> 200 ng/ml) and decreasing thereafter. There was no detectable increase in serum VEGF levels. Maximal collateral perfusion, a principal correlate of collateral development and angiogenesis, was equivalent in all groups. CONCLUSION: Adenoviral-mediated gene transfer is capable of inducing sustained VEGF165 expression in the pericardium; however, locally targeted pericardial VEGF delivery failed to improve myocardial collateral perfusion in this model.

Pharmacodynamics of basic fibroblast growth factor: route of administration determines myocardial and systemic distribution.

OBJECTIVE: We have shown that basic fibroblast growth factor (bFGF/FGF-2) enhances myocardial collateral development in a canine model of progressive coronary occlusion when delivered via the left atrial or intracoronary routes; however, we have found intravenous bFGF ineffective in the same model. Data on the fate and efficacy of intravenous bFGF are limited. We hypothesized that first pass lung uptake might limit myocardial bFGF availability after intravenous injection. We postulated that delivery of bFGF through the distal port of a wedged Swan Ganz catheter might circumvent this problem by restricting exposure of bFGF to a limited number of pulmonary binding sites. This study evaluated differential regional uptake of 125I labeled bFGF following bolus intravenous, Swan Ganz, left atrial, intracoronary, and pericardial delivery. METHODS: Mongrel dogs were used. Human recombinant bFGF, monoiodinated with 125I, was mixed with cold bFGF to a specific activity of 0.03 microCi/microgram. Approximately 100 micrograms/kg was injected per animal by the intravenous, left atrial, Swan Ganz, intracoronary, or pericardial route. Dogs were killed 15 min or 150 min later. The heart, lungs, liver, spleen, and kidneys were harvested and 125I activity was assessed. Immunohistochemical and pharmacokinetic studies were also performed. RESULTS: Serum half life of bFGF was comparable after intracoronary, intravenous and left atrial delivery (50 min); however, there were significant differences with regard to pharmacodynamics. After intracoronary administration, 3-5% of the total bFGF dose was recovered from the heart, with the peptide immunolocalized to the extracellular matrix and vascular endothelium. In contrast, only 1.3% of the injected bFGF was localized to the heart after left atrial administration and 0.5% was recovered after intravenous or Swan Ganz delivery. Pericardial administration resulted in substantial cardiac bFGF delivery; 19% was present at 150 min. Myocardial uptake was similar with Swan Ganz and intravenous delivery, suggesting that the administered dose did not saturate available pulmonary binding sites. CONCLUSIONS: These data predict efficacy of intracoronary, left atrial, and pericardial bFGF for myocardial angiogenesis, and a lack of efficacy after bolus intravenous and Swan Ganz administration.

The magnitude of inotropic reserve is unrelated to basal systolic function or wall thickness in patients with chronic ischemic left ventricular dysfunction.

Forty-four patients with coronary artery disease and left ventricular dysfunction underwent transesophageal echocardiography with dobutamine infusion to investigate the relation between basal contractile function and inotropic reserve. No significant relation was observed between basal percent systolic thickening or diastolic thickness and the maximum increase in contractile function in response to dobutamine, thus emphasizing the heterogenity of the mechanisms by which coronary stenoses may affect contraction at rest and inotropic reserve in these patients.

Effects of a single intracoronary injection of basic fibroblast growth factor in stable angina pectoris.

We sought to evaluate safety, tolerability, pharmacokinetics, and pharmacodynamics of basic fibroblast growth factor (bFGF), administered as a single intracoronary injection, to subjects with stable angina pectoris secondary to coronary artery disease. bFGF, an angiogenic growth factor, has been shown to enhance collateral development in animal models of progressive coronary occlusion. To our knowledge, this study represents the initial introduction of parenteral bFGF into humans. This was a phase 1, randomized, dose-escalation trial of bFGF in 25 subjects with coronary artery disease and stable angina. Subjects were randomized 2:1 to a single dose of bFGF or placebo, injected into the left main coronary artery. bFGF doses ranged from 3 to 100 microg/kg, increasing in half-log increments. bFGF was generally well tolerated at doses of 3 to 30 microg/kg. Plasma clearance was 20 +/- 2 ml/kg/min, with an elimination half-life of 85 +/- 11 minutes. bFGF caused acute hypotension ( approximately 10%) that did not appear to be dose-related through the dose range studied. Of the 9 subjects who received 30 to 100 microg/kg bFGF, 2 had sustained hypotension, mild to moderate in severity, lasting 1 to 3 days, and 3 subjects developed bradycardia hours to days after bFGF administration. bFGF dilated epicardial coronary arteries (7.4 +/- 2.5% mean diameter increase, p <0.02). Transient mild thrombocytopenia and proteinuria were observed in some subjects in the 30-microg/kg cohort. No subject had signs suggesting systemic angiogenesis. Thus, intracoronary bFGF, at doses of 3 to 30 microg/kg, was generally well tolerated in subjects with stable angina.

Combined bromodeoxyuridine immunohistochemistry and Masson trichrome staining: facilitated detection of cell proliferation in viable vs. infarcted myocardium.

Cells in the S-phase of the cell cycle can be identified in tissue sections by immunohistochemical localization of the thymidine analogue bromodeoxyuridine (BrdU). Generally, a single counterstain is used to visualize the underlying tissue; however, interpretation of morphologic detail is often difficult. We have utilized BrdU to localize proliferating cells in myocardium exposed to angiogenic mitogens. To facilitate identification of labelled nuclei in the context of infarcted vs. viable myocardium, BrdU immunohistochemistry was followed by a modified Masson trichrome stain. The time of exposure to the counterstains and the wash protocol were re-revised, permitting clear identification of the labelled brown nuclei against a background of red viable myocardium vs. blue infarct. The combined technique also provides color contrast suitable for computer-based image analysis.

Heparin promotes the formation of extracardiac to coronary anastomoses in a canine model.

We developed a canine model for the in vivo utilization of angiogenesis factors to promote revascularization of a collateral-dependent area of the heart and assessed the potential of heparin in this preparation. Ameroids were placed on the proximal left anterior descending coronary artery (LAD) of 29 dogs, and the left internal mammary artery (IMA) was implanted in an intramyocardial tunnel in proximity to the LAD. A tube positioned in the distal IMA provided a continuous retrograde infusion directly into the vessel from an implanted pump. Heparin (15 or 150 U/h) or saline vehicle was infused. After 8 wk, regional myocardial blood flow was assessed in the anesthetized state during adenosine-induced vasodilatation, before and during occlusion of the IMA. The IMA provided a greater proportion of maximal collateral flow in heparin-treated dogs (22 +/- 5%, n = 17) than in saline-treated dogs (9 +/- 2%, n = 12, P less than 0.05). Thus continuous infusion of heparin promotes the formation of collaterals between the extracardiac artery and the myocardial circulation, establishing the feasibility of targeting angiogenic agents for myocardial revascularization.

Creation of anastomoses between an extracardiac artery and the coronary circulation. Proof that myocardial angiogenesis occurs and can provide nutritional blood flow to the myocardium.

The purpose of this investigation was to determine whether blood vessels could develop de novo between an extracardiac artery and a collateral-dependent zone of the heart and to quantify the nutritive blood flow afforded by the new vessels. We also adapted the preparation so that angiogenically active agents could be chronically administered directly to the site of neovascularization in subsequent studies. To induce neovascularization between a systemic artery and the coronary circulation, the left internal mammary artery (IMA) was implanted in an intramyocardial tunnel in proximity to the left anterior descending coronary artery (LAD). A tube situated in the distal IMA connected to an implanted pump provided for continuous intra-arterial infusion at the site of angiogenesis. During the same procedure, an ameroid constrictor was placed on the proximal LAD, rendering its perfusion territory collateral dependent during a 2-3 week period. After 8 weeks, the functional capacity of the anastomoses established between the implanted IMA and the LAD territory was assessed by determining regional myocardial blood flow under basal conditions, during adenosine-induced vasodilatation, and during differential occlusions of the IMA and left circumflex coronary artery (LCCA). For all dogs, IMA occlusion decreased maximal LAD territory flow from 1.31 +/- 0.11 to 1.16 +/- 0.10 ml/min/g (p less than 0.005). Occlusion of the LCCA decreased LAD zone flow to 0.73 +/- 0.12 ml/min/g, whereas occlusion of the IMA in addition to the LCCA further decreased LAD zone flow to 0.42 +/- 0.11 ml/min/g (p less than 0.02). The IMA provided measurable nutritive blood flow in seven of 12 dogs, and in these dogs, the artery provided 30.0 +/- 2.5% of total LAD zone collateral conductance under conditions of maximal vasodilatation (range, 23-42%). We conclude that angiogenesis can occur between an implanted internal mammary artery and the native coronary circulation in dogs, providing modest nutritive blood flow to a collateral-dependent region. Further studies will be necessary to determine whether direct, local infusion of angiogenically active factors can enhance neovascularization and whether sufficient flow can be reliably supplied to make some variant of this approach clinically applicable.

Neointimal proliferation in canine coronary arteries. A model of restenosis permitting local and continuous drug delivery.

BACKGROUND: A number of experimental preparations have been used to elucidate the pathophysiology of restenosis after percutaneous transluminal coronary angioplasty; however, few models have been advanced that address restenosis in coronary arteries, and none provides an effective means of continuous local drug delivery. In this report, we describe a model of restenosis in coronary arteries with the provision for local, continuous delivery of cytotoxic and/or anti-proliferative agents. EXPERIMENTAL DESIGN: An ameroid constrictor was placed on the left circumflex coronary artery of 17 normocholesterolemic dogs. One month later, after substantial collateral development had ensued, a segment of the left circumflex coronary artery distal to the ameroid was mechanically compressed using surgical forceps for 10 (N = 4), 15 (N = 4), 20 (N = 2), or 30 minutes (N = 5). In two dogs, an indwelling left circumflex catheter and implanted pump maintained a continuous infusion of saline at the injury site. In addition, the pump side port provided transcutaneous access for serial, selective coronary arteriography. The animals were maintained on a normal diet, without cholesterol or fat supplementation. RESULTS: Three weeks after vascular injury, significant neointimal proliferation was observed in all dogs that was morphologically similar to the proliferation seen after percutaneous transluminal coronary angioplasty in human coronary arteries. The extent of neointimal formation was linearly related to the duration of injury: neointimal/medial area ratios were 0.35 +/- 0.10, 0.46 +/- 0.10, 0.58 +/- 0.03, and 1.16 +/- 0.26 (mean +/- SE) after 10, 15, 20, and 30 minutes of mechanical compression injury, respectively. CONCLUSIONS: This model produces striking neointimal proliferation in the coronary arteries of normocholesterolemic dogs, morphologically similar to that seen in human coronary restenosis specimens. The model appears suitable to test the efficacy of agents with the potential to inhibit neointimal formation, providing continuous intracoronary drug delivery, as well as transcutaneous access for serial, selective arteriography.

Histological evaluation of the canine retinal vasculature following chronic systemic administration of basic fibroblast growth factor.

The purpose of the present study was to determine if prolonged systemic arterial administration of basic fibroblast growth factor (bFGF) at a dose sufficient to enhance collateral vessel formation in the ischaemic hearts of dogs would produce retinal neovascularisation in these same animals. Adult dogs (15-25 kg) were subjected to gradual occlusion of a coronary artery and randomised to receive 1 of 3 treatments via an indwelling left atrial catheter: (1) bFGF 1.74 mg/d, 5 d/wk for 63 d (n = 7); (2) bFGF 1.74 mg/d, 5 d/wk, for 35 d followed by physiological saline, 5 d/wk, for 28 d (n = 10); or (3) physiological saline, 5 d/wk, for 63 d (n = 10). After 63 d the retinal vasculatures from these dogs were isolated and examined for capillary varicosity, neovascularisation and other histopathological signs of angiopathy. All data were collected under masked conditions. The results suggest that chronic, systemic arterial administration of bFGF stimulates neovascularisation in the ischemic myocardium, but has no significant structural or vasoproliferative effect on the nonischaemic retina of the same animal.

Extracardiac to coronary anastomoses support regional left ventricular function in dogs.

Intramyocardial implantation of a systemic artery [the internal mammary artery (IMA)] causes angiogenesis, with formation of systemic to coronary anastomoses. In dogs, we assessed the magnitude of IMA-derived nutritive flow and determined its influence on regional contraction. We also sought to determine whether acidic fibroblast growth factor (FGF), an angiogenic peptide, could enhance myocardial neovascularization. Ameroid constrictors and hydraulic balloon occluders were placed on the left anterior descending coronary artery (LAD) of 23 dogs, and the left IMA was implanted in the LAD territory. Dogs were randomized to receive continuous infusions of acidic FGF with heparin, heparin alone, or placebo directly into the IMA for 8 wk. Regional myocardial blood flow was assessed in the conscious state 3 days and 8 wk after operation. Left ventricular function was determined in the anesthetized state at the 8-wk conclusion of treatment. In all dogs, IMA occlusion reduced mean maximal LAD zone perfusion by 28% (P < 0.001), without influencing regional contraction. When IMA occlusion was superimposed on left circumflex coronary artery (LCX) occlusion, LAD zone perfusion declined by 34% (relative to LCX occlusion alone), significantly impairing regional contraction. Treatment with either acidic FGF plus heparin or heparin alone improved IMA-derived collateral flow; however, addition of acidic FGF to heparin afforded no additional advantage over heparin by itself. We conclude that acidic FGF did not enhance myocardial angiogenesis in this model. IMA-derived collateral flow has significant functional importance; however, it is evident in the dog only when other sources of collateral flow are compromised.

Myocardial blood flow at rest and contractile reserve in patients with chronic coronary artery disease and left ventricular dysfunction.

BACKGROUND: The mechanisms that determine chronic left ventricular dysfunction in coronary artery disease (in particular, critical reductions in coronary artery blood flow leading to hibernating myocardium) may affect the ability of the myocardium to respond to inotropic stimulation with dobutamine. This study was designed to investigate the relationship between resting myocardial blood flow and contractile reserve in patients with coronary artery disease and chronic left ventricular dysfunction. METHODS AND RESULTS: Twenty-three patients (21 men and 2 women; age 61 +/- 9 years) underwent transesophageal echocardiography during infusion of dobutamine (2.5 microg/kg to 40 microg/kg per minute) and positron emission tomography (PET) with 150-water (9 patients) or 13N-ammonia (14 patients). Systolic wall thickening at each dose of dobutamine and resting myocardial blood flow were quantitatively analyzed in 8 anatomically matched regions at mid-ventricular level. Myocardial regions with preserved contraction had higher blood flow compared with regions with basal dyssynergy (0.99 +/- 0.3 vs 0.65 +/- 0.3 mL/min/gm; P < .0001). Among myocardial regions with preserved resting contraction, no relation was observed between blood flow and the response to dobutamine (r = 0.06). In contrast, among myocardial regions with diminished resting contraction, a significant correlation was observed between resting blood flow and contractile reserve (r = 0.53; P < .0001). The maximum increase in percent systolic wall thickening with dobutamine was 32.8% +/- 14% in regions with normal blood flow, 21.5% +/- 17% in regions with mildly to moderately reduced blood flow, and 10.7% +/- 10% in regions with severely reduced blood flow (P < .0001). CONCLUSIONS: These findings emphasize the importance of resting myocardial blood flow for the preservation of contractile reserve in patients with coronary artery disease and left ventricular dysfunction. Because a positive inotropic response to dobutamine is more likely to occur in dyssynergic regions with preserved rather than reduced myocardial blood flow, regional perfusion may determine in which circumstances dobutamine echocardiography contributes to the assessment of myocardial viability.