John P. Tessmer

Ischemia-Induced Coronary Collateral Growth Is Dependent on Vascular Endothelial Growth Factor and Nitric Oxide

Background—We hypothesized that ischemia-induced expression of vascular endothelial growth factor (VEGF) and the production of NO stimulate coronary collateral growth. Methods and Results—To test this hypothesis, we measured coronary collateral blood flow and VEGF expression in myocardial interstitial fluid in a canine model of repetitive myocardial ischemia under control conditions and during antagonism of NO synthase. Collateralization was induced by multiple (1/h; 8/d), brief (2 minutes) occlusions of the left anterior descending coronary artery for 21 days. In controls, collateral blood flow (microspheres) progressively increased to 89±9 mL · min−1 · 100 g−1 on day 21, which was equivalent to perfusion in the normal zone. Reactive hyperemic responses (a measure of the severity of ischemia) decreased as collateral blood flow increased. In NG-nitro-l-arginine methyl ester (L-NAME)– and L-NAME+nifedipine–treated dogs, to block the production of NO and control hypertension, respectively, collateral blood flow did not increase and reactive hyperemia was robust throughout the occlusion protocol (P <0.01 versus control). VEGF expression (Western analyses of VEGF164 in myocardial interstitial fluid) in controls peaked at day 3 of the repetitive occlusions but waned thereafter. In sham-operated dogs (instrumentation but no occlusions), expression of VEGF was low during the entire protocol. In contrast, VEGF expression was elevated throughout the 21 days of repetitive occlusions after L-NAME. Reverse transcriptase–polymerase chain reaction analyses revealed that the predominant splice variant expressed was VEGF164. Conclusions—NO is an important regulator of coronary collateral growth, and the expression of VEGF is induced by ischemia. Furthermore, the induction of coronary collateralization by VEGF appears to require the production of NO.

Cardiovascular Effects of Xenon in Isoflurane-anesthetized Dogs with Dilated Cardiomyopathy

Background Clinical interest in xenon has been rekindled recently by new recycling systems that have decreased its relative cost. The cardiovascular effects of xenon were examined in isoflurane‐anesthetized dogs before and after the development of rapid left ventricular (LV) pacing‐induced cardiomyopathy. Methods Dogs (n = 10) were chronically instrumented to measure aortic and LV pressure, LV subendocardial segment length, and aortic blood flow. Hemodynamics were recorded, and indices of LV systolic and diastolic function and afterload were determined in the conscious state and during 1.5 minimum alveolar concentration isoflurane anesthesia alone and combined with 0.25, 0.42, and 0.55 minimum alveolar concentration xenon in dogs with and without cardiomyopathy. Results Administration of xenon to healthy dogs anesthetized with isoflurane decreased heart rate and increased the time constant [small tau, Greek] of isovolumic relaxation but did not alter arterial and LV pressures, preload recruitable stroke work slope, and indices of LV afterload. Chronic rapid LV pacing increased the baseline heart rate and LV end‐diastolic pressure, decreased arterial and LV systolic pressures, and produced LV systolic and diastolic dysfunction. Administration of xenon to isoflurane‐anesthetized, cardiomyopathic dogs did not alter heart rate, arterial and LV pressures, myocardial contractility, and indices of early LV filling and regional chamber stiffness. More pronounced increases in [small tau, Greek] were accompanied by increases in total arterial resistance during administration of xenon to isoflurane‐anesthetized cardiomyopathic compared with healthy dogs. Conclusions The results indicate that xenon produces minimal cardiovascular actions in the presence of isoflurane in dogs with and without experimental dilated cardiomyopathy.

Angiostatin Inhibits Coronary Angiogenesis During Impaired Production of Nitric Oxide

Background—The in vivo mechanism by which inhibition of NO synthase impairs ischemia-induced coronary vascular growth is unknown. We hypothesized that production of the growth inhibitor angiostatin increases during decreased NO production, blunting angiogenesis and collateral growth. Methods and Results—Measurements were made in myocardial tissue or interstitial fluid (MIF) from dogs undergoing repetitive coronary occlusions under control conditions or during antagonism of NO synthase (NG-nitro-l-arginine methyl ester [L-NAME]) for 7, 14, or 21 days. A sham group was instrumented identically but received no occlusions. In controls, capillary density in the ischemic zone increased initially but returned to baseline at the later times. In the L-NAME group, capillary density was lower at 7 days compared with that of controls. MIF from control dogs induced in vitro endothelial tube formation and cell proliferation, significantly greater than that from the L-NAME group. MIF from shams did not stimulate tube formation. In controls or shams, tube formation or cell proliferation did not change after administration of antiangiostatin, but this antibody restored the responses to control levels in the L-NAME group. Angiostatin expression in MIF was increased in the L-NAME group compared with controls and shams. The activities of tissue matrix metalloproteinases (MMPs) MMP-2 and MMP-9, which generate angiostatin, were increased in the L-NAME group. Conclusions—Inhibition of NO synthase increased expression of angiostatin and activities of MMP-2 and MMP-9. Our findings indicate that angiostatin inhibits coronary angiogenesis during compromised NO production and may underscore the impairment of coronary angiogenesis during endothelial dysfunction.

Levosimendan Enhances Left Ventricular Systolic and Diastolic Function in Conscious Dogs with Pacing-induced Cardiomyopathy

We examined the left ventricular (LV) mechanical actions of levosimendan (LSM) before and after the development of pacing-induced cardiomyopathy in conscious dogs chronically instrumented for measurement of aortic and LV pressure, +dP/dt, subendocardial segment length, and cardiac output (CO). The slope (Mw) of the regional preload recruitable stroke work relation was used to assess myocardial contractility. Diastolic function was evaluated with a time constant of isovolumic relaxation (tau), the maximal rate of segment-lengthening velocity (dL/dt), and a regional chamber-stiffness constant (Kp). On different experimental days, dogs were assigned to receive LSM (12- or 24-microgram/kg loading dose and 0.2 or 0.4 microgram/kg/min infusion) before rapid ventricular pacing was initiated. Dogs were then paced at 240 beats/min for 22 +/- 2 days, and the low and high doses of LSM were repeated on separate days. LSM increased Mw and +dP/dt in dogs before the initiation of pacing, consistent with enhanced myocardial contractility. LSM also improved indices of LV diastolic function (decreases in tau and Kp and increases in dL/dt) in dogs before pacing. Rapid ventricular pacing over a 3-week period increased LV end-diastolic pressure and produced systolic (decreases in Mw and +dP/dt) and diastolic (increases in tau and Kp and decreases in dL/dt) dysfunction. LSM significantly (p < 0.05) increased Mw (54 +/- 3 to 98 +/- 6 mm Hg) +dP/dt and dL/dt (57 +/- 13 to 72 +/- 13 mm/s) and decreased tau (66 +/- 4 to 52 +/- 3 ms) and Kp (1.14 +/- 0.14 to 0.71 +/- 0.03 mm-1) in the presence of LV dysfunction. In contrast to the findings in normal dogs, however, LSM did not alter heart rate and calculated indices of myocardial oxygen consumption in dogs after pacing. The findings indicate that LSM produces favorable alterations in hemodynamics and positive inotropic and lusitropic effects in conscious dogs with left ventricular dysfunction.

Systemic and coronary hemodynamic actions and left ventricular functional effects of levosimendan in conscious dogs

We examined the effects of levosimendan, a new myofilament Ca2+ sensitizer with phosphodiesterase (PDE)-inhibiting properties, on systemic and coronary hemodynamics and left ventricular (LV) systolic and diastolic function in conscious dogs with intact and blocked autonomic nervous system (ANS) reflexes. Twenty experiments were conducted in 10 dogs chronically instrumented for measurement of aortic and LV pressure, the peak rate of increase and decrease in LV pressure (+ dP/dtmax and -dP/dtmin), subendocardial segment length, diastolic coronary blood flow (CBF) velocity, and cardiac output (CO). The slope (Mw) of the regional preload recruitable stroke work relation was used to assess myocardial contractility. Diastolic function was evaluated by -dP/dtmin, a time constant of isovolumic relaxation (τ), maximum segment lengthening velocity during rapid ventricular filling (dL/dtmax), and a regional chamber stiffness constant (Kp). Dogs were randomly assigned to receive levosimendan (0.5, 1.0, 2.0, and 4.0 μg · kg−1 · min−1) with or without ANS blockade. On separate experimental days, systemic and coronary hemodynamics and LV pressure-segment length diagrams and waveforms were recorded after 10-min equilibration at each dose in the conscious ANS-intact or ANS-blocked state. Levosimendan increased heart rate (HR), CO, mean and diastolic CBF velocity, and pressure-work index (PWI, an estimate of myocardial oxygen consumption) and decreased LV end-diastolic pressure (EDP), systemic vascular resistance (SVR), end-systolic and end-diastolic segment length, and mean and diastolic coronary vascular resistance (CVR) in dogs with intact ANS function. Levosimendan-induced increases in HR and PWI and decreases in SVR were attenuated by ANS blockade. Levosimendan caused equivalent dose-dependent increases in Mw in ANS-intact and ANS-blocked dogs, consistent with a positive inotropic effect independent of ANS activity. Levosimendan decreased τ (e.g., 35 ± 1 ms during control to 29 ± 1 ms at the high dose) and increased the magnitude of LV – dPldtmin in dogs with intact but not blocked ANS reflexes, suggesting that relaxation was enhanced by favorable changes in systemic hemodynamics or ANS activation and direct effects of this drug on lusitropic state. Levosimendan also increased dL/dtmax to a greater degree in ANS-intact dogs, indicating that improvement of rapid ventricular filling was also partially dependent on ANS tone. No changes in Kp were observed in either experimental group. The results indicate that levosimendan decreases preload and afterload and has positive inotropic and lusitropic properties. The actions of levosimendan on diastolic function are largely mediated by the ANS.

Perfusion of ischemic myocardium during anesthesia with sevoflurane.

BackgroundSevoflurane produces direct vasodilation of coronary arteries in vitro and decreases coronary vascular resistance in vivo, pharmacologic properties that may contribute to the development of “coronary steal.” This investigation examined the effects of sevoflurane on the distribution of regional myocardial perfusion in chronically instrumented dogs with steal-prone coronary artery anatomy. MethodsDogs were chronically instrumented for measurement of aortic and left ventricular pressure, diastolic coronary blood flow velocity and subendocardial segment length. After recovery from surgery, dogs underwent repetitive, brief, left anterior descending coronary artery (LAD) occlusions via an implanted hydraulic vascular occluder to enhance collateral development. A progressive left circumflex coronary artery (LCCA) stenosis was also obtained using an ameroid constrictor. After development of LCCA stenosis, the LAD was totally occluded to produce a model of multivessel coronary artery disease. Systemic hemodynamics, regional contractile function and myocardial perfusion measured with radioactive microspheres were assessed in the conscious state and during sevoflurane anesthesia at 1.0 and 1.5 MAC with and without restoration of arterial blood pressure and heart rate to conscious levels. ResultsTotal LAD occlusion with simultaneous LCCA stenosis increased heart rate, mean arterial pressure, left ventricular systolic and end-diastolic pressures, end-diastolic segment length, and rate-pressure product in conscious dogs. Subsequent administration of sevoflurane caused dose-related decreases in arterial pressure, left ventricular systolic pressure, double product, and peak rate of increase of left ventricular pressure at 50 mmHg. Perfusion of normal myocardium was unchanged during sevoflurane anesthesia. In contrast, sevoflurane caused dose-dependent decreases in blood flow to myocardium supplied by the stenotic LCCA, which returned to control levels after restoration of heart rate and arterial pressure. No reduction in collaterally derived blood flow to the occluded region was produced by 1.0 or 1.5 MAC sevoflurane. No redistribution of blood flow away from the occluded LAD region to normal or stenotic myocardium occurred during sevoflurane anesthesia. in fact, increases in the ratio of blood flow between occluded and normal zones or occluded and stenotic zones were observed in the subepicardium during 1.5 MAC sevoflurane with maintenance of the heart rate and arterial pressure at conscious levels. ConclusionsThe results demonstrate that sevoflurane does not reduce or abnormally redistribute myocardial blood flow derived from coronary collateral vessels in a chronically instrumented canine model of multlvessel coronary artery obstruction.

A novel alpha2-adrenoceptor antagonist attenuates the early, but preserves the late cardiovascular effects of intravenous dexmedetomidine in conscious dogs☆

OBJECTIVES To test the hypothesis that L-659,066, a peripherally acting alpha 2-adrenoceptor agonist, will abolish the early pressor response but preserve the late depressor action of intravenous dexmedetomidine in conscious, unsedated dogs. DESIGN A prospective investigation. SETTING A laboratory research. PARTICIPANTS Nine chronically instrumented dogs. INTERVENTIONS Dogs received dexmedetomidine, 5 micrograms/kg intravenously, in the presence or absence of L-659,066, 0.1, 0.2, or 0.4 mg/kg intravenously, pretreatment in a random fashion determined with a Latin square design on different experimental days. MEASUREMENTS AND MAIN RESULTS Systemic and coronary hemodynamics were assessed under control conditions, 30 minutes after administration of L-659,066 and 5 and 60 minutes after intravenous administration of dexmedetomidine. Dexmedetomidine alone acutely increased mean arterial pressure (106 +/- 3 to 175 +/- 4 mmHg; p < 0.05), left ventricular (LV) systolic and end-diastolic pressures, systemic vascular resistance (3,400 +/- 350 to 13,360 +/- 2,290 dyne.s.cm-5; p < 0.05), and coronary vascular resistance (2.69 +/- 0.19 to 4.18 +/- 0.43 mmHg.Hz-1.10(-2); p < 0.05) and decreased LV +dP/dtmax and cardiac output (2.6 +/- 0.3 to 1.3 +/- 0.2 L/min; p < 0.05). Dexmedetomidine alone decreased heart rate, mean arterial pressure, and LV systolic pressure and caused sustained reductions in +dP/dtmax and cardiac output up to 60 minutes after administration. L-659,066 alone increased heart rate, +dP/dtmax, cardiac output, and coronary blood flow velocity and decreased systemic vascular resistance. Mean arterial and LV pressures and coronary vascular resistance were unchanged. Pretreatment with L-659,066 abolished the acute dexmedetomidine-induced increases in mean arterial pressure, LV pressures, systemic and coronary vascular resistance and decreases in +dP/dtmax and cardiac output. In contrast, reductions in mean arterial pressure and LV systolic pressure observed 60 minutes after administration of dexmedetomidine were preserved in dogs receiving L-659,066. Cardiac performance, systemic vascular resistance, and coronary hemodynamics were also maintained to a greater degree 60 minutes after dexmedetomidine administration in the presence of L-659,066. CONCLUSION L-659,066 prevents the immediate pressor effects of 5 micrograms/kg of intravenous dexmedetomidine but preserves the majority of the late beneficial cardiovascular effects of this selective alpha 2-adrenoceptor agonist in conscious dogs.

Repetitive coronary artery occlusions induce release of growth factors into the myocardial interstitium.

Our objective was to delineate the temporal sequence of mitogenic activity in myocardial interstitial fluid (IF) during enhancement of collateral growth. Collateral development in chronically instrumented dogs was induced by eight 2-min coronary occlusions/day for 21 days. Collateralization was assessed by measurement of blood flow in the region distal to a total coronary occlusion. Myocardial IF was obtained periodically from an intramyocardial catheter, and mitogenic activity was assessed by proliferative response of cultured endothelial cells (EC) and vascular smooth muscle cells (VSMC) to the IF. Three experiments were conducted to test that the mitogenic activity is induced by protein growth factors: 1) protein digestion of the myocardial IF with Pronase-coupled latex beads; 2) heat inactivation (boiling) of the IF; and 3) neutralization of the mitogenic activity with antibodies for basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). Blood flow was reconstituted to baseline levels during occlusion after 3 wk of repetitive coronary occlusions. After initiation of occlusion the mitogenic activity of the myocardial IF on VSMC and EC increased up to days 12-14 and was reduced on days 19-23. Pronase treatment and heat inactivation blocked the mitogenic effect. Treatment with antibodies for bFGF and VEGF neutralized the proliferative response to the myocardial IF at specific times. bFGF antibody inhibited the mitogenic effect significantly on days 12-14. VEGF antibody neutralized the mitogenicity of the myocardial IF on day 7, days 12 and 13, and days 19 and 20significantly. We conclude that myocardial IF harvested from ischemic myocardium is highly mitogenic up to 2 wk after initiation of repetitive coronary occlusions. After 3 wk of ischemia, the degree of mitogenic activity for VSMC and EC was decreased from peak levels. The antibodies could not neutralize the mitogenic effect of the myocardial IF during this time period. These results suggest that mitogens are expressed during various stages of collateral development in a time-dependent manner, that the mitogens are proteinaceous in nature, and that bFGF and VEGF are released into the myocardial IF.Our objective was to delineate the temporal sequence of mitogenic activity in myocardial interstitial fluid (IF) during enhancement of collateral growth. Collateral development in chronically instrumented dogs was induced by eight 2-min coronary occlusions/day for 21 days. Collateralization was assessed by measurement of blood flow in the region distal to a total coronary occlusion. Myocardial IF was obtained periodically from an intramyocardial catheter, and mitogenic activity was assessed by proliferative response of cultured endothelial cells (EC) and vascular smooth muscle cells (VSMC) to the IF. Three experiments were conducted to test that the mitogenic activity is induced by protein growth factors: 1) protein digestion of the myocardial IF with Pronase-coupled latex beads; 2) heat inactivation (boiling) of the IF; and 3) neutralization of the mitogenic activity with antibodies for basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). Blood flow was reconstituted to baseline levels during occlusion after 3 wk of repetitive coronary occlusions. After initiation of occlusion the mitogenic activity of the myocardial IF on VSMC and EC increased up to days 12-14 and was reduced on days 19-23. Pronase treatment and heat inactivation blocked the mitogenic effect. Treatment with antibodies for bFGF and VEGF neutralized the proliferative response to the myocardial IF at specific times. bFGF antibody inhibited the mitogenic effect significantly on days 12-14. VEGF antibody neutralized the mitogenicity of the myocardial IF on day 7, days 12 and 13, and days 19 and 20 significantly. We conclude that myocardial IF harvested from ischemic myocardium is highly mitogenic up to 2 wk after initiation of repetitive coronary occlusions. After 3 wk of ischemia, the degree of mitogenic activity for VSMC and EC was decreased from peak levels. The antibodies could not neutralize the mitogenic effect of the myocardial IF during this time period. These results suggest that mitogens are expressed during various stages of collateral development in a time-dependent manner, that the mitogens are proteinaceous in nature, and that bFGF and VEGF are released into the myocardial IF.

Sevoflurane selectively increases coronary collateral blood flow independent of KATP channels in vivo.

BACKGROUND Volatile anesthetic agents produce coronary vasodilation via activation of adenosine triphosphate-sensitive potassium (KATP) channels. The authors tested the hypothesis that sevoflurane selectively increases coronary collateral blood flow and assessed the role of KATP channel activation in this process. METHODS Experiments were conducted in dogs 8 weeks after long-term implantation of a left anterior descending coronary artery (LAD) ameroid constrictor to stimulate coronary collateral growth. Dogs were instrumented for measurement of retrograde LAD blood flow (an index of large coronary collateral blood flow) and LAD tissue flow (via radioactive microspheres; an index of small collateral blood flow). Coronary collateral perfusion and normal (left circumflex coronary artery [LCCA]) zone tissue blood flow were determined in four groups of dogs pretreated with intracoronary glyburide (50 microg/kg) or vehicle in the presence or absence of sevoflurane (1 minimum alveolar concentration). Dose-response relationships to the KATP channel agonist nicorandil were established in each dog using doses (25, 50, and 100 microg/min) previously shown to increase coronary collateral blood flow. RESULTS Sevoflurane increased blood flow through large and small collaterals and increased collateral vascular conductance in the presence of glyburide but did not affect LCCA blood flow or conductance. In contrast, nicorandil increased blood flow through small but not large collaterals. Nicorandil also increased LCCA blood flow and conductance, actions that were attenuated by glyburide. CONCLUSIONS The results demonstrate that sevoflurane selectively increases large and small coronary collateral blood flow via mechanism(s) independent of KATP channel activation.

Desflurane and Isoflurane Exert Modest Beneficial Actions on Left Ventricular Diastolic Function during Myocardial Ischemia in Dogs

Background Volatile anesthetics exert cardioprotective effects during myocardial ischemia. This investigation examined the regional systolic and diastolic mechanical responses to brief left anterior descending coronary artery (LAD) occlusion in the central ischemic zone and in remote normal myocardium in the conscious state and during desflurane and isoflurane anesthesia.