Infusion of light chains from patients with cardiac amyloidosis causes diastolic dysfunction in isolated mouse hearts.

BACKGROUND: Primary (AL) amyloidosis is a plasma cell dyscrasia characterized by clonal production of immunoglobulin light chains (LC) resulting in the subsequent systemic deposition of extracellular amyloid fibrils. Cardiac involvement is marked by the hemodynamic pattern of impaired diastolic filling and restrictive cardiomyopathy. Although cardiac death in patients with AL amyloidosis is usually associated with extensive myocardial infiltration, the infiltration alone does not correlated with the degree of heart failure or survival. We hypothesized that circulating monoclonal LC may directly impair cardiac function, in addition to any mechanical effects of amyloid fibril deposition. Therefore, we examined the effects of amyloid LC proteins on diastolic and systolic cardiac function, as measured in an isolated mouse heart model. METHODS AND RESULTS: LC were obtained from patients with nonamyloid disease or from those with noncardiac, mild cardiac, and severe cardiac involved AL amyloidosis. Saline or LC (100 microgram/mL) was infused into a Langendorff-perfused, isovolumically contracting mouse heart. Saline and control, noncardiac, and mild-cardiac LC infusions did not alter ex vivo cardiac function. In contrast, infusion of sever cardiac LC resulted in marked impairment of ventricular relaxation with preservation of contractile function. CONCLUSION: These results demonstrate that infusion of LC from patients with AL amyloidosis result in diastolic dysfunction similar to that observed in patients with cardiac involved AL amyloidosis, and they suggest that amyloid LC proteins may contribute directly to the pathogenesis and the rapid progression of amyloid cardiomyopathy, independent of extracellular fibril deposition.

Mice lacking inducible nitric oxide synthase have improved left ventricular contractile function and reduced apoptotic cell death late after myocardial infarction.

Nitric oxide produced by inducible nitric oxide synthase (NOS2) has been implicated in the pathophysiology of chronic myocardial remodeling and failure. We tested the role of NOS2 in left ventricular (LV) remodeling early (1 month) and late (4 months) after myocardial infarction (MI) in mice lacking NOS2. MI size measured 7 days, 1 month, and 4 months after MI was the same in NOS2 knockout (KO) and wild-type (WT) mice. The LV end-diastolic pressure-volume relationship measured by the isovolumic Langendorff technique showed a progressive rightward shift from 1 to 4 months after MI in WT mice. LV developed pressure measured over a range of LV volumes was reduced at 1 and 4 months after MI in WT mice (P<0.05 and P<0.01 versus shams, respectively). In KO mice, the rightward shift was similar to that in WT mice at 1 and 4 months after MI, as was peak LV developed pressure at 1 month after MI. In contrast, at 4 months after MI, peak LV developed pressure in KO mice was higher than in WT mice (P<0.05 versus WT) and similar to that in sham-operated mice. At 1 month after MI, the frequency of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive myocytes in the remote myocardium was increased to a similar extent in WT and KO mice. At 4 months after MI, the frequency of apoptotic myocytes was increased in WT mice but not in KO mice (P<0.05 versus WT). Improved contractile function and reduced apoptosis were associated with reduced mortality rate in KO mice at 4 months after MI. Thus, NOS2 does not play an important role in determining infarct size or early LV remodeling during the first month after MI. In contrast, during late (ie, 4 months after MI) remodeling, NOS2 in remote myocardium contributes to decreased contractile function, increased myocyte apoptosis in remote myocardium, and reduced survival.

Exercise training attenuates age-associated diastolic dysfunction in rats.

BACKGROUND: In contrast to systolic function, which is relatively well preserved with advancing age, diastolic function declines steadily after age 30. Our goal was to determine whether changes in diastolic function that occur with aging could be reversed with exercise training. Methods and Results-- Adult (6-month-old) and old (24-month-old) Fischer 344/BNF1 rats were studied after either 12 weeks of treadmill training or normal sedentary cage life. Three aspects of diastolic function were studied: (1) left ventricular (LV) filling in vivo via Doppler echocardiograph, (2) LV passive compliance, and (3) the degree of ischemia-induced LV stiffening. Maximal exercise capacity was lower in the old rats (18+/-1 minutes to exhaustion on a standard treadmill) than in the adult rats (25+/-1 minutes). Training increased exercise capacity by 43% in the old rats and 46% in the adults (to 26+/-1 and 37+/-1 minutes, respectively). Echocardiographic indices of LV relaxation were significantly lower in the old rats, but with training, they increased back to the levels seen in the adults. LV stiffness measured in the isolated, perfused hearts was not affected by age or training. Also in the isolated hearts, the LV stiffened more rapidly during low-flow ischemia in the old hearts than in the adults, but training eliminated this age-associated difference in the response to ischemia. CONCLUSIONS: Our findings indicate that in rats, some age-associated changes in diastolic function are reversible and thus may not be intrinsic to aging but instead secondary to other processes, such as deconditioning.

Left ventricular diastolic dysfunction during demand ischemia: rigor underlies increased stiffness without calcium-mediated tension. Amelioration by glycolytic substrate.

OBJECTIVES: The goal of this study was to determine the subcellular mechanism(s) underlying increased left ventricular (LV) diastolic chamber stiffness (DCS) during angina (demand ischemia). BACKGROUND: Increased DCS may result from increased diastolic myocyte calcium concentration and/or rigor. Therefore, we assessed the effects of direct alterations of both calcium-activated tension and high-energy phosphates on increased DCS. METHODS: Demand ischemia was reproduced in isolated, isovolumic, red-cell perfused rabbit hearts by imposing low-flow ischemia and pacing tachycardia. This resulted in increased DCS. Interventions were performed after LV end-diastolic pressure had increased approximately 7 mm Hg. Initially, to determine the effects of altered calcium concentration or myofilament calcium responsiveness, hearts received either: 1) 5 or 14 mmol/L calcium chloride; 2) 8 mmol/L egtazic acid; 3) 5 mmol/L butane-dione-monoxime (BDM); or 4) 50 mmol/L ammonium chloride (NH4Cl). Then, to assess the contribution of decreased high-energy phosphate supply, hearts received 5) glucose (25 mmol/L) and insulin (400 microU/ml). RESULTS: 1) Calcium chloride, 5 and 14 mmol/L, increased LV systolic pressure by 42% and 70%, respectively (p < 0.001), indicating increased calcium-activated tension, but did not further increase DCS, implying intact diastolic calcium resequestration. 2) Egtazic acid reduced LV systolic pressure by 30% (p < 0.001), indicating reduced intracellular calcium, but failed to reduce increased DCS. 3) Butane-dione-monoxime and NH4Cl chloride affected contractile function (i.e., a calcium-driven force) but did not alter increased DCS. 4) Glucose and insulin, which increase high-energy phosphates during ischemia, reduced increased DCS by 50% (p < 0.001). CONCLUSIONS: Increased DCS during demand ischemia was insensitive to maneuvers altering intracellular calcium concentration or myofilament calcium-responsiveness, that is, evidence against an etiology of calcium-activated tension. In contrast, increased glycolytic substrate ameliorated increased DCS, supporting a primary mechanism of rigor-bond formation.

Exaggerated left ventricular dilation and reduced collagen deposition after myocardial infarction in mice lacking osteopontin.

Osteopontin (OPN), an extracellular matrix protein, is expressed in the myocardium with hypertrophy and failure. We tested the hypothesis that OPN plays a role in left ventricular (LV) remodeling after myocardial infarction (MI). Accordingly, OPN expression and LV structural and functional remodeling were determined in wild-type (WT) and OPN knockout (KO) mice 4 weeks after MI. Northern analysis showed increased OPN expression in the infarcted region, peaking 3 days after MI and gradually decreasing over the next 28 days. In the remote LV, OPN expression was biphasic, with peaks at 3 and 28 days. In situ hybridization and immunohistochemical analyses showed increased OPN mRNA and protein primarily in the interstitium. Infarct size, heart weight, and survival were similar in KO and WT mice after MI (P=NS), whereas the lung wet weight/dry weight ratio was increased in the KO mice (P<0.005 versus sham-operated mice). Peak LV developed pressure was reduced to a similar degree after MI in the KO and WT mice. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive myocytes was similar in KO and WT mice after MI. In contrast, post-MI LV chamber dilation was approximately twice as great in KO versus WT mice (P<0.001). Myocyte length increased after MI in WT mice (P<0.001) but not in KO mice. Electron microscopy showed increased collagen content in WT mice after MI but not in KO mice after MI. Type I collagen content was increased approximately 3-fold and approximately 7-fold in remote and infarcted regions, respectively, of WT hearts after MI but not in KO hearts (P<0.01 versus WT hearts). Likewise, Northern analyses showed increased collagen I(alpha(1)) mRNA after MI in remote regions of WT hearts but not in KO hearts. Thus, increased OPN expression plays an important role in regulating post-MI LV remodeling, at least in part, by promoting collagen synthesis and accumulation.

Cell therapy attenuates deleterious ventricular remodeling and improves cardiac performance after myocardial infarction.

BACKGROUND: Myocardial infarction (MI) promotes deleterious remodeling of the myocardium, resulting in ventricular dilation and pump dysfunction. We examined whether supplementing infarcted myocardium with skeletal myoblasts would (1) result in viable myoblast implants, (2) attenuate deleterious remodeling, and (3) enhance in vivo and ex vivo contractile performance. METHODS AND RESULTS: Experimental MI was induced by 1-hour coronary ligation followed by reperfusion in adult male Lewis rats. One week after MI, 10(6) myoblasts were injected directly into the infarct region. Three groups of animals were studied at 3 and 6 weeks after cell therapy: noninfarcted control (control), MI plus sham injection (MI), and MI plus cell injection (MI+cell). In vivo cardiac function was assessed by maximum exercise capacity testing and ex vivo function was determined by pressure-volume curves obtained from isolated, red cell-perfused, balloon-in-left ventricle (LV) hearts. MI and MI+cell hearts had indistinguishable infarct sizes of approximately 30% of the LV. At 3 and 6 weeks after cell therapy, 92% (13 of 14) of MI+cell hearts showed evidence of myoblast graft survival. MI+cell hearts exhibited attenuation of global ventricular dilation and reduced septum-to-free wall diameter compared with MI hearts not receiving cell therapy. Furthermore, cell therapy improved both post-MI in vivo exercise capacity and ex vivo LV systolic pressures. CONCLUSIONS: Implanted skeletal myoblasts form viable grafts in infarcted myocardium, resulting in enhanced post-MI exercise capacity and contractile function and attenuated ventricular dilation. These data illustrate that syngeneic myoblast implantation after MI improves both in vivo and ex vivo indexes of global ventricular dysfunction and deleterious remodeling and suggests that cellular implantation may be beneficial after MI.

Exercise intolerance in rats with hypertensive heart disease is associated with impaired diastolic relaxation.

A decrease in functional capacity is one of the most important clinical manifestations of hypertensive heart disease, but its cause is poorly understood. Our purpose was to evaluate potential causes of hypertension-induced exercise intolerance, focusing on identifying the type(s) of cardiac dysfunction associated with the first signs of exercise intolerance during the course of hypertensive heart disease. Exercise capacity was measured weekly in Dahl salt-sensitive rats as they developed hypertension as well as in Dahl salt-resistant control rats. Exercise capacity was unchanged from baseline during the first 8 weeks of hypertension, suggesting that hypertension itself did not cause exercise intolerance. After 9 to 12 weeks of hypertension, exercise capacity decreased in salt-sensitive rats but not in control rats. After 10 weeks of hypertension, indices of diastolic function (early truncation of the E wave), as assessed by echocardiography at rest, were decreased in the salt-sensitive rats. When exercise capacity had decreased by approximately 25% in a rat, the heart was isolated, and left ventricular (LV) compliance and systolic function were measured. At that time point, LV hypertrophy was modest (an approximately 20% increase in LV mass), and systolic function was normal or supernormal, indicating that exercise intolerance began during "compensated" LV hypertrophy. Passive LV compliance remained normal in salt-sensitive rats. Thus, in this model of hypertensive heart disease, exercise intolerance develops during the compensated stage of LV hypertrophy and appears to be due to changes in diastolic rather than systolic function. However, studies in which LV function is assessed during exercise are needed to conclusively define the roles of systolic and diastolic dysfunction in causing exercise intolerance.

ET(A)-receptor blockade prevents matrix metalloproteinase activation late postmyocardial infarction in the rat.

Endothelin (ET) A (ET(A)) receptors activate matrix metalloproteinases (MMP). Since endothelin-1 (ET) is increased in myocardium late postmyocardial infarction (MI), we hypothesized that stimulation of ET(A) receptors contributes to activation of myocardial MMPs late post-MI. Three days post-MI, rats were randomized to treatment with the ET(A)-selective receptor antagonist sitaxsentan (n = 12) or a control group (n = 12). Six weeks later, there were rightward shifts of the left ventricular (LV) end-diastolic and end-systolic pressure-volume relationships, as measured ex vivo by the isovolumic Langendorff technique. Both shifts were markedly attenuated by sitaxsentan. In LV myocardium remote from the infarct, the activities of MMP-1, MMP-2, and MMP-9 were increased in the post-MI group, and the increases were prevented by sitaxsentan treatment. Expression of tissue inhibitor of MMP-1 was decreased post-MI, and the decrease was prevented by sitaxsentan treatment. Chronic post-MI remodeling is associated with activation of MMPs in myocardium remote from the infarct. Inhibition of ET(A) receptors prevents MMP activation and LV dilation, suggesting that ET, acting via the ET(A) receptor, contributes to chronic post-MI remodeling by its effects on MMP activity.

Metabolic support as an adjunct to inotropic support in the hypoperfused heart.

In situations such as severe low-flow ischemia, where myocardial work output is low and dependence on anaerobic glycolysis is high, increasing the myocardial supply of glucose and insulin is cardioprotective. Our goal was to determine whether this strategy of "metabolic support" would also be cardioprotective in the moderately hypoperfused heart receiving inotropic stimulation, i.e. when myocardial work was near normal, and reliance on anaerobic glycolysis was minimal. Isovolumic left ventricular performance and cardiac energetics (31P-NMR spectroscopy) were measured in 20 isolated rat hearts perfused with red blood cell containing perfusate (hematocrit 40%) with either normal (5 m M, 15 microU/ml) or increased (19.5 m M, 250 microU/ml) glucose and insulin in addition to normal levels of lactate and free fatty acids. Lowering global coronary flow to 30% of normal decreased left ventricle developed pressure by 50%. Administering dobutamine for 40 min restored developed pressure to 95+/-13% of baseline but caused diastolic pressure to increase by 23+/-6 mmHg and [ATP] to decrease by 44+/-6%. Glucose and insulin prevented the increase in end-diastolic pressure, and [ATP] fell by only 14+/-3%. Despite these improvements in cardiac energetics and diastolic function, left ventricle developed pressure was not improved by increased glucose and insulin during, or after the hypoperfusion. We conclude that inotropic support of the hypoperfused heart can cause new diastolic dysfunction, but that this diastolic dysfunction can be eliminated by preserving myocardial high-energy phosphates with increased glucose and insulin.

Lack of direct role for calcium in ischemic diastolic dysfunction in isolated hearts.

BACKGROUND: Ischemia is characterized by an increase in intracellular calcium and occurrence of diastolic dysfunction. We investigated whether the myocyte calcium level is an important direct determinant of ischemic diastolic dysfunction. METHODS AND RESULTS: We exposed isolated, perfused isovolumic (balloon in left ventricle) rat and rabbit hearts to low-flow ischemia and increased extracellular calcium (from 1.5 to 16 mmol/L) for brief periods. Intracellular calcium was measured by aequorin. Low-flow ischemia resulted in a 270% increase (P:<0.05) in diastolic intracellular calcium, a 50% (P:<0.05) calcium transient amplitude decrease, and a 52% (P:<0.05) slowing of calcium transient decline. Diastolic pressure increased by 6+/-2 mm Hg (P:<0.05), and rate of systolic pressure decay decreased by 65% (P:<0.05). Experimentally increasing extracellular calcium doubled both intracellular diastolic calcium and calcium transient amplitude, concomitant with a developed pressure increase; however, there was no increase in ischemic diastolic pressure, slowing of the calcium transient decay, or further slowing of systolic pressure decay. Similarly, after 45 minutes of low-flow ischemia, after diastolic pressure had increased from 8.5+/-0.6 to 19.7+/-3.5 mm Hg (P:<0.001), intracoronary high-molar calcium chloride infusion increased systolic pressure from 36+/-4 to 63+/-11 mm Hg (P:<0.001), indicating an increase in intracellular calcium, but it decreased diastolic pressure from 19. 7+/-3.5 to 17.5+/-3.7 mm Hg (P:<0.01). Conversely, EGTA infusion decreased systolic pressure, indicating a decrease in intracellular calcium, but did not decrease diastolic pressure. CONCLUSIONS: When calcium availability was experimentally altered during ischemia, there was no alteration in left ventricular diastolic pressure, suggesting that ischemic diastolic dysfunction is not directly mediated by a calcium activated tension.

Altered beta-adrenergic signal transduction in nonfailing hypertrophied myocytes from Dahl salt-sensitive rats.

Desensitization of the beta-adrenergic receptor (beta-AR) response is well documented in hypertrophied hearts. We investigated whether beta-AR desensitization is also present at the cellular level in hypertrophied myocardium, as well as the physiological role of inhibitory G (G(i)) proteins and the L-type Ca(2+) channel in mediating beta-AR desensitization. Left ventricular (LV) myocytes were isolated from hypertrophied hearts of hypertensive Dahl salt-sensitive (DS) rats and nonhypertrophied hearts of normotensive salt-resistant (DR) rats. Cells were paced at a rate of 300 beats/min at 37 degrees C, and myocyte contractility and intracellular Ca(2+) concentration ([Ca(2+)](i)) were simultaneously measured. In response to increasing concentrations of isoproterenol, DR myocytes displayed a dose-dependent augmentation of cell shortening and the [Ca(2+)](i) transient amplitude, whereas hypertrophied DS myocytes had a blunted response of both cell shortening and the [Ca(2+)](i) transient amplitude. Interestingly, inhibition of G(i) proteins did not restore beta-AR desensitization in DS myocytes. The responses to increases in extracellular Ca(2+) and an L-type Ca(2+) channel agonist were also similar in both DS and DR myocytes. Isoproterenol-stimulated adenylyl cyclase activity, however, was blunted in hypertrophied myocytes. We concluded that compensated ventricular hypertrophy results in a blunted contractile response to beta-AR stimulation, which is present at the cellular level and independent of alterations in inhibitory G proteins and the L-type Ca(2+) channel.

Impaired cell shortening and relengthening with increased pacing frequency are intrinsic to the senescent mouse cardiomyocyte.

Increased heart rate enhances cardiac contractility and accelerates relaxation. Both the force- and relaxation-frequency relationships are critical to myocardial function, especially during stress, and have been shown to be impaired in senescent myocardium. While senescent myocardium is characterized by decreased sarcoplasmic reticulum calcium ATPase activity, it is unclear if altered calcium regulation is directly responsible for the attenuated contractility and relaxation observed with increasing pacing frequency in aged myocardium. We examined this issue using freshly dissociated left ventricular myocytes, isolated from young adult and senescent mouse hearts. Myocytes were paced from 2 to 9 Hz at 37 degrees C, and cell shortening and [Ca(2+)](i)were simultaneously measured using video edge-detection and fura-2 fluorescence, respectively. In adult myocytes, increasing the pacing rate resulted in a progressive increase in percent cell shortening (CS) (P<0.01). This positive CS-frequency relationship was paralleled by an increase in [Ca(2+)](i)transient amplitude (P<0.05). In contrast, the CS-frequency relationship was blunted in senescent myocytes with no increase in percent CS or [Ca(2+)](i)transient amplitude with increasing pacing rate. With increased pacing, the decreases in time constants (tau) of cell relengthening and Ca(2+)transient decay were much steeper in adult compared to senescent myocytes (P<0.05). This study demonstrates that adult mouse myocytes exhibit augmented intracellular Ca(2+)transient amplitude and enhanced intracellular Ca(2+)removal with increasing pacing frequency, resulting in increased cell shortening and enhanced relengthening with frequency. In contrast, senescent mouse myocytes exhibit impaired calcium handling with increasing pacing frequency, which correlated with impairment of both cell shortening and relengthening.

Progressive left ventricular remodeling and apoptosis late after myocardial infarction in mouse heart.

We tested the hypothesis that left ventricular (LV) remodeling late after myocardial infarction (MI) is associated with myocyte apoptosis in myocardium remote from the infarcted area and is related temporally to LV dilation and contractile dysfunction. One, four, and six months after MI caused by coronary artery ligation, LV volume and contractile function were determined using an isovolumic balloon-in-LV Langendorff technique. Apoptosis and nuclear morphology were determined by terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) and Hoechst 33258 staining. Progressive LV dilation 1-6 mo post-MI was associated with reduced peak LV developed pressure (LVDP). In myocardium remote from the infarct, there was increased wall thickness and expression of atrial natriuretic peptide mRNA consistent with reactive hypertrophy. There was a progressive increase in the number of TUNEL-positive myocytes from 1 to 6 mo post-MI (2.9-fold increase at 6 mo; P < 0. 001 vs. sham). Thus LV remodeling late post-MI is associated with increased apoptosis in myocardium remote from the area of ischemic injury. The frequency of apoptosis is related to the severity of LV dysfunction.

Comparison of hearts with 2 types of pressure-overload left ventricular hypertrophy.

Comparisons of myocardium remodeled by the 2 most common causes of left ventricular hypertrophy (LVH), hypertension and aortic constriction, are limited. We hypothesized that important differences may exist in the myocardium of hearts with these 2 origins of "pressure overload" LVH. Accordingly, we studied isolated hearts from 3 groups of Dahl salt-sensitive rats, controls, and hearts with matched amounts of LVH secondary to either hypertension or aortic constriction. Isovolumic LV function and myocardial energetics ((31)P nuclear magnetic resonance spectroscopy) were measured as coronary flow was lowered to 16% of baseline for 48 minutes. During this low-flow ischemia, isovolumic end-diastolic pressure, a measure of LV stiffness, increased to 52+/-4 mm Hg in controls and 51+/-6 mm Hg in aortic banded hearts but to only 35+/-5 mm Hg in hearts with hypertensive LVH. In all hearts, the P(i) resonance in the (31)P nuclear magnetic resonance spectrum, whose position indicates myocardial pH, split into 2 peaks during low-flow ischemia, which indicates distinct regions of pH 6.9 (moderate acidosis) and pH 6.2 (severe acidosis). Concentrations of ATP, PCr, P(i), and H(+) of the moderately acidotic region were not different among groups. However, the size of the severely acidotic region was smallest in the hypertensive LVH hearts, and in all 3 groups, the size of this region correlated (r(2)=0.65 to 0.80) with the degree of LV stiffening. We conclude that in Dahl rats, LVH secondary to hypertension protects against ischemia-induced diastolic dysfunction by minimizing the size of the region of severe acidosis.

Increased diastolic chamber stiffness during demand ischemia: response to quick length change differentiates rigor-activated from calcium-activated tension.

BACKGROUND: Increased diastolic chamber stiffness (increased DCS) during angina (demand ischemia) has been postulated to be generated by increased diastolic myocyte calcium concentration. METHODS AND RESULTS: We reproduced demand ischemia in isolated isovolumically contracting red-cell-perfused rabbit hearts by imposing pacing tachycardia during global low coronary blood flow (32% of baseline). This increased lactate production without increasing oxygen consumption and resulted in increased DCS (isovolumic left ventricular end-diastolic pressure [LVEDP] increased 10 mm Hg, P<0. 001, n=38). To determine the mechanism of increased DCS, we assessed responses to a quick-stretch-release maneuver (QSR), in which the intraventricular balloon was rapidly inflated and deflated to achieve a 3% circumferential muscle fiber length change. QSR was first validated as an effective method of discriminating between calcium-driven and rigor-mediated increased DCS. QSR imposed during demand ischemia when DCS had increased (LVEDP pretachycardia versus posttachycardia, 15+/-1 versus 27+/-2 mm Hg, P<0.001, n=6) reduced DCS to pretachycardia values (LVEDP post-QSR, 15+/-1 mm Hg, P<0.001), ie, elicited a response characteristic of rigor, without any component of calcium-generated tension. CONCLUSIONS: A rigor force, possibly resulting from high-energy phosphate depletion and/or an increase in ADP, appears to be the primary mechanism underlying increased DCS in this model of global LV demand ischemia.

ATP synthesis during low-flow ischemia: influence of increased glycolytic substrate.

BACKGROUND: Our goals were to (1) simulate the degree of low-flow ischemia and mixed anaerobic and aerobic metabolism of an acutely infarcting region; (2) define changes in anaerobic glycolysis, oxidative phosphorylation, and the creatine kinase (CK) reaction velocity; and (3) determine whether and how increased glycolytic substrate alters the energetic profile, function, and recovery of the ischemic myocardium in the isolated blood-perfused rat heart. METHODS AND RESULTS: Hearts had 60 minutes of low-flow ischemia (10% of baseline coronary flow) and 30 minutes of reperfusion with either control or high glucose and insulin (G+I) as substrate. In controls, during ischemia, rate-pressure product and oxygen consumption decreased by 84%. CK velocity decreased by 64%; ATP and phosphocreatine (PCr) concentrations decreased by 51% and 63%, respectively; inorganic phosphate (P(i)) concentration increased by 300%; and free [ADP] did not increase. During ischemia, relative to controls, the G+I group had similar CK velocity, oxygen consumption, and tissue acidosis but increased glycolysis, higher [ATP] and [PCr], and lower [P(i)] and therefore had a greater free energy yield from ATP hydrolysis. Ischemic systolic and diastolic function and postischemic recovery were better. CONCLUSIONS: During low-flow ischemia simulating an acute myocardial infarction region, oxidative phosphorylation accounted for 90% of ATP synthesis. The CK velocity fell by 66%, and CK did not completely use available PCr to slow ATP depletion. G+I, by increasing glycolysis, slowed ATP depletion, maintained lower [P(i)], and maintained a higher free energy from ATP hydrolysis. This improved energetic profile resulted in better systolic and diastolic function during ischemia and reperfusion. These results support the clinical use of G+I in acute MI.

Angiotensin II receptor blockade attenuates the deleterious effects of exercise training on post-MI ventricular remodelling in rats.

OBJECTIVES: The effects of exercise training on LV remodelling following large anterior myocardial infarction (MI) remains controversial. Blockade of the renin-angiotensin system has been shown to prevent ventricular dilation and deleterious remodeling. We therefore tested, in a rat model of chronic MI, whether any potentially deleterious effects of exercise on post-MI remodelling could be ameliorated by angiotensin II receptor blockade. METHODS: Male Wistar rats underwent coronary ligation or sham operation. Treatment with losartan (10 mg/kg/day) began 1 week post-MI and moderate treadmill exercise (25 m/min, 60 min/day, 5 days/week) was initiated 2 weeks post-MI. Systolic and diastolic pressure-volume relationships were measured in isolated, red-cell perfused, isovolumically beating hearts 8 weeks post-MI. Morphometric measurements were performed in trichrome stained cross sections of the heart. Five groups of animals were compared: sham (n=13), control MI (MI; n=11), MI plus losartan (MI-Los; n=13), MI plus exercise (MI-Ex; n=10) and MI plus exercise and losartan (MI-Ex-Los; n=12). RESULTS: Infarct size (% of left ventricle, LV) was similar among the infarcted groups [MI=43+/-4%, MI-Los=49+/-2%, MI-Ex=45+/-1%, MI-Ex-Los=48+/-2% (NS)]. Exercise, losartan and exercise+losartan treatments all attenuated LV dilation post-MI to a similar degree. Exercise training increased LV developed pressure in both untreated and losartan treated hearts (P<0.05 vs. other MI groups). In addition, exercise resulted in additional scar thinning in untreated hearts, while no additional scar thinning was seen in post-infarct hearts receiving both losartan and exercise. CONCLUSIONS: Following large anterior MI, losartan attenuated LV dilation and scar thinning. In untreated animals, exercise decreased dilation, but also contributed to scar thinning. Therefore, exercise concurrent with blockade of the renin-angiotensin system may provide optimal therapeutic benefit following large anterior MI.

Increased glycolytic substrate protection improves ischemic cardiac dysfunction and reduces injury.

Early clinical trials of glucose-insulin-potassium for acute myocardial infarction were inconclusive. However, several recent placebo-controlled, prospective, randomized clinical trials of glucose-insulin-potassium for acute myocardial infarction or metabolic support during and after cardiac surgery have demonstrated its efficacy. These clinical results are supported by experimental studies that have shown a strong protective effect of increased glycolytic substrate on ischemic myocardium in concert with an improved bioenergetic status.

Impaired lusitropy-frequency in the aging mouse: role of Ca(2+)-handling proteins and effects of isoproterenol.

We examined the relationship between age-associated lusitropic impairment, heart rate, and Ca(2+)-handling proteins and assessed the efficacy of increasing left ventricular (LV) relaxation via beta-adrenergic stimulation in adult and aging mouse hearts. LV function was measured in isolated, isovolumic blood-perfused hearts from adult (5 mo), old (24 mo), and senescent (34 mo) mice. Hearts were paced from 5 to 10 Hz, returned to 7 Hz, exposed to 10(-6) M isoproterenol, and paced again from 7 to 10 Hz. Age-related alterations in Na(+)/Ca(2+) exchanger (NCX), sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA2a), and phospholamban (PLB) levels were assessed by immunoblot. Despite preserved contractile performance, aging caused impaired lusitropy. Increased pacing caused an elevation in end-diastolic pressure that progressively worsened with age. The time constant of isovolumic pressure decay (tau) was significantly prolonged in old and senescent hearts compared with adults. Relative to adult hearts, the SERCA2a-to-PLB ratios were reduced 68 and 69%, and NCX were reduced 37 and 58% in old and senescent hearts, respectively. Isoproterenol completely reversed the age-associated lusitropic impairments. These data suggest that impaired lusitropy in aging mouse hearts is related to a decreased rate of cytosolic Ca(2+) removal and that accelerating SR Ca(2+) resequestration via beta-adrenergic stimulation can reverse this impairment.

Immediate effect of aortic valve replacement for aortic stenosis on left ventricular diastolic chamber stiffness.

Diastolic dysfunction is common after coronary artery bypass surgery, and we hypothesized that left ventricular (LV) hypertrophy associated with aortic stenosis may lead to worsening LV diastolic function after aortic valve replacement for aortic stenosis. Transesophageal echocardiographic LV images and simultaneous pulmonary arterial wedge pressures were used to define the LV diastolic pressure cross-sectional area relation before and immediately after aortic valve replacement for aortic stenosis in 14 patients. In all patients, LV diastolic chamber stiffness increased, as evidenced by a leftward shift in the LV diastolic pressure cross-sectional area relation. At comparable LV filling (pulmonary arterial wedge) pressures the mean LV end-diastolic cross-sectional area preoperatively was 17.9 +/- 1.7 cm2, but decreased by 32% after aortic valve replacement to 12.1 +/- 1.2 cm2 (p = 0.0001). In conclusion, after aortic valve replacement, diastolic chamber stiffness increased in all patients.