The functional-morphological state of the myocardium in experimental massive embolism of the pulmonary artery]

A comparative study of hemodynamic and structural-metabolic changes in the myocardium of the right (RV) and left ventricles (LV) in acute massive pulmonary artery embolism was made in 19 mongrel dogs. In the control group the activity of SDH, MDH, GDH, NADH-DH in LV were higher than in RV. The numeral density and relative area of mitochondrial profile surface in LV was higher that in RV. A significant increase in afterload on RV causes intensification of cell respiration, a rise in numeral density and relative area of mitochondrial profile surface. Weakening of LV work leads to contrary structural-metabolic changes. Thus, contrary changes in hemodynamic loads on RV and LV in acute compensative massive pulmonary artery embolism correlated with contrary changes in their cell metabolism.     

Time course of right ventricular remodeling in rats with experimental myocardial infarction

Right ventricular (RV) weight increases dependent on time after myocardial infarction (MI) and on MI size. The sequential changes in RV volume and hemodynamics and their relations to left ventricular (LV) remodeling after MI are unknown. We therefore examined the time course of RV remodeling in rats with LV MI. MI was produced by left coronary artery ligation. Four, eight, and sixteen weeks later, LV and RV hemodynamic measurements were performed and pressure-volume curves were obtained. For serial measurement of RV volumes and performance, cine-MRI was performed 2 and 8 wk after MI. The ratios of beta-myosin heavy chain (MHC) to alpha-MHC and skeletal to cardiac alpha-actin were determined for the RV and LV after large MI or sham operation. RV weight increased in rats with MI, as did RV volume. RV pressure-volume curves were shifted toward larger volumes 16 wk after large MI. RV systolic pressure increased gradually over time; however, the gain in RV weight was always in excess of RV systolic pressure. The ratios of skeletal to cardiac alpha-actin and beta-MHC to alpha-MHC were increased after MI in both ventricles in a similar fashion. Because RV wall stress was not increased after infarction, mechanical factors may not conclusively explain hypertrophy, which maintained balanced loading conditions for the RV even after large LV infarction.     

Myosin ATPase in young and old mammalian myocardium: responses to exercise in cold and thermo neutral environment

Resting levels of blood lactate (La) were significantly lower at 35 degrees C than at 25 degrees C in the trained (Tr) rats while untrained (UTr) rats maintained higher levels. Extent of decrease in blood glucose (Glu) in Tr rats was lower in cold (C) than in thermo neutral (N) water in young but not in old. Training in C had no impact on young right and left ventricles (RV and LV). UTr old rats showed loss in LV Glu at both the temperatures. Old trainees had reduced RV Glu in C while no change was observed at N. Substrate changes were concomitant with altered myosin ATPase activity. Young ventricles showed higher ATPase activity in LV than in RV, and training in C evoked elevations in RV enzyme. The results suggest that training may enhance the functional and biochemical activity in terms of higher myosin ATPase activity in N, as against a C environment, and the effect is better pronounced in LV. Anaerobic condition is felt more in C as seen through elevated blood La.     

Load-insensitive measurements from an isolated perfused biventricular working rat heart

To determine whether a rat heart model can provide load-insensitive measurements of cardiac function, a recently developed biventricular perfused preparation was tested. Using 29 Sprague-Dawley rat hearts perfused with modified Krebs-Henseleit buffer, ventricles functioned simultaneously with adjustable independent preload (venous reservoirs) and afterload (compliance chambers). Ultrasonic crystal pairs provided continuous left (LV) and right ventricular (RV) short-axis dimensions. LV and RV pressure-length loops (loop area = work) were generated from paired intraventricular pressure and short-axis dimensions. Load-insensitive measurements were obtained from the slopes (elastance) and x-intercepts (L₀) of regression lines generated from the end-systolic coordinates of these pressure-length loops over ranges of RV and LV preloads. Measurements were made after 15 min of stable function and after 20 min of warm (37°C) ischemia. During perturbations in LV afterload, there were linear changes in dP/dt, but loop work remained relatively unchanged. RV dP/dt and work varied little with physiologic ranges of afterload. Increased RV afterload had little effect on LV function. Ischemia affected LV function more than RV function using these measurements. Elastance, however, increased after ischemia with diastolic creep (increased L₀) for both ventricles. Load-insensitive and other sophisticated hemodynamic measurements are possible with this new preparation.     

Changes in the expression and/or activation of regulatory proteins in rat hearts adapted to chronic hypoxia

Chronic intermittent high altitude (IHA) hypoxia results in long-term adaptation protecting the heart against acute ischemia/reperfusion injury; however, molecular mechanisms of this phenomenon are not completely elucidated so far. The present study was aimed at investigation of a modulating effect of IHA hypoxia on the expression and/or activation of selected regulatory proteins, with particular emphasis on differential responses in the right ventricle (RV) and left ventricle (LV). Adult male Wistar rats were exposed to IHA hypoxia of 7000 m simulated in a hypobaric chamber (8 h/day, 25 exposures), and protein contents and activities in myocardial fractions were determined by Western blot analysis. In markedly hypertrophic RV of hypoxic rats, gelatinolytic activity of MMP-2 and protein levels of carbonic anhydrase IX (a marker of hypoxia) were significantly enhanced. Study of mitogen-activated protein kinases (MAPKs) revealed no differences in the contents of total p38-MAPK in both ventricles between the IHA and normoxic control rats, whereas activation of p38-MAPK was decreased in the RV and moderately increased in the LV of IHA rats as compared to controls. Extracellular signal regulated kinase-2 (ERK-2) was partially up-regulated in the RV of IHA rats, and, in addition, expression of acidic fibroblast growth factor (aFGF), a potential activator of ERK cascade, was also significantly increased. In contrast, expression of ERKs in the LV as well as their activities in both ventricles, were not affected by IHA hypoxia. Differential effects of IHA hypoxia on c-Jun-N-terminal protein kinases (JNKs) in the RV and LV were also observed. As compared with the controls, total content of JNKs was increased in the RV of the IHA rats, while expression of JNKs in the LV was down-regulated. IHA hypoxia changed neither total levels of Akt kinase in both RV and LV, nor Akt kinase activity in the RV. However, increased levels of activated phospho-Akt kinase were found in the LV of IHA rats. The results demonstrate that adaptation of rat hearts to chronic IHA hypoxia is associated with disctinct changes in the levels and/or activation of several regulatory proteins in two ventricles. The latter could be attributed to both myocardial remodeling and cardioprotection induced by chronic hypoxia.     

Lesions of ventricular cardiomyocytes in experimental massive pulmonary embolism]

The damage of ventricular myocardial cells during acute experimental massive pulmonary embolism (MPE) was studied by light, polarization and electron microscopy on anaesthetized dogs. In cases, when MPE was followed by heart failure, the deep ir reversible damage of myofibrils took place, and the relative volume of myofibrils decreased in both ventricles. The damage of right ventricular myocardium, which works against increased postload during MPE, may be reason of right ventricular insufficiency.     

Interstrain differences in changes in 5-nucleotidase activity in mouse macrophages in response to immunostimulation

The effect of immunostimulants on the activity of 5-nucleotidase in the macrophages of peritoneal exudate (MPE) has been investigated in mice of various strains. It has been demonstrated that in case of subcutaneous introduction of immunostimulants interstrain differences might be observed in the changes of MPE 5-nucleotidase activity. The decrease in the enzymatic activity in MPE was found to be the most pronounced in C57Bl/6 mice, while in AKR mice it was the least marked. CBA and C3 mice revealed no changes in MPE 5-nucleotidase activity in response to immunostimulation.     

Downregulation of right ventricular phosphodiesterase PDE-3A mRNA and protein before the development of canine heart failure

Phosphodiesterase III (PDE-3) inhibitors are inotropes used to treat congestive heart failure (HF). Previous studies showed PDE-3A mRNA levels were reduced in the left ventricle (LV) in dogs subjected to pacing-induced HF. The present study evaluated a time-course for RV-specific changes in PDE-3A mRNAs and proteins after pacing for 3 wk (n=4) or in HF (4–5 wk;n=4–6). Total RNA from LV/RV tissues was isolated for Northern analyses; cytosolic and microsomal proteins were prepared for PDE-3A immunoblots. PDE-3A mRNAs (7–8 and 10 kb) were normalized against glyceraldehyde-3-phosphodehydrogenase (GAPDH) or ribosomal 18s with similar results. PDE-3A/GAPDH ratios in 3 wk were unchanged in LV, but significantly (p<0.05) reduced by 48% in RV vs unpaced controls (n=8). In contrast, PDE-3A (7–8kb)/GAPDH ratios were significantly reduced in HF by 50–59% in both ventricles. Consistent with mRNA levels, significant reductions in microsomal 135 kDa (93–96%) and cytosolic 120 kDa PDE-3A (57–69%) were seen in both ventricles in HF or in the RV at 3 wk; an LV-specific reduction (50%) in cytosolic 80 kDa PDE-3A in HF was also detected. In summary, RV-specific downregulation of PDE-3A mRNA/protein(s) at 3 wk suggests that hemodynamic rather than humoral mechanisms are responsible, and provides a molecular basis for the limited efficacy of milrinone in the progression of HF.     

Hemodynamics and right-ventricle functional characteristics of a swine carotid artery-jugular vein shunt model of pulmonary arterial hypertension: An 18-month experimental study

The continuous changes in pulmonary hemodynamic properties and right ventricular (RV) function in pulmonary arterial hypertension (PAH) have not been fully characterized in large animal model of PAH induced by a carotid artery–jugular vein shunt. A minipig model of PAH was induced by a surgical anastomosis between the left common carotid artery and the left jugular vein. The model was validated by catheter examination and pathologic analyses, and the hemodynamic features and right-ventricle functional characteristics of the model were continuously observed by Doppler echocardiography. Of the 45 minipigs who received the surgery, 27 survived and were validated as models of PAH, reflected by mean pulmonary artery pressure ≥25 mmHg, and typical pathologic changes of pulmonary arterial remodeling and RV fibrosis. Non-invasive indices of pulmonary hemodynamics (pulmonary artery accelerating time and its ratio to RV ventricular ejection time) were temporarily increased, then reduced later, similar to changes in tricuspid annular displacement. The Tei index of the RV was elevated, indicating a progressive impairment in RV function. Surgical anastomosis between carotid artery and jugular vein in a minipig is effective to establish PAH, and non-invasive hemodynamic and right-ventricle functional indices measured by Doppler echocardiography may be used as early indicators of PAH.     

Differential expression of stress proteins in rat myocardium after free wheel or treadmill run training.

High-intensity treadmill exercise increases the expression of a cardioprotective, inducible 72-kDa stress protein (SP72) in cardiac muscle. This investigation examined whether voluntary free wheel exercise training would be sufficient to confer a similar response. Male Sprague-Dawley rats were randomly assigned to either treadmill (TM-Tr) or free wheel (FW-Tr) training groups. By the end of the 8-wk training period, TM-Tr animals ran 1 h/day, 5 days/wk up a 10% grade, covering a distance of 8,282 m/wk. FW-Tr rats ran, on average, 5,300 m/wk, with one-third of the animals covering distances similar to those for the TM-Tr group. At the time of death, hearts of trained and caged sedentary control (Sed) animals were divided into left (LV) and right (RV) ventricles. Citrate synthase activity and the relative immunoblot contents of SP72, SP73 (the constitutive isoform of the SP70 family), and a 75-kDa mitochondrial chaperone (SP75) were subsequently determined. LV and RV did not differ on any measure, and SP73, SP75, and citrate synthase were not affected by training. Cardiac SP72 levels were elevated over fourfold in both ventricles of TM-Tr compared with RV of FW-Sed rats. Despite the animals having run a similar total distance, cardiac SP72 content in FW-Tr rats was not different from that in Sed animals. These data indicate that voluntary exercise training is insufficient to elicit an elevation of SP72 in rat heart and suggest that exercise intensity may be a critical factor in evoking the cardioprotective SP72 response.     

K-FGF mediated transformation and induction of metastatic potential involves altered ornithine decarboxylase and S-adenosylmethionine decarboxylase expression – role in cellular invasion

Adult male Wistar rats were exposed to intermittent high altitude hypoxia of 7000 m simulated in a hypobaric chamber for 8 h/day, 5 days a week; the total number of exposures was 25. The concentration of individual phospholipids and their fatty acid (FA) profile was determined in right (RV) and left (LV) ventricles. Adaptation to hypoxia decreased the concentration of diphosphatidylglycerol (DPG) in hypertrophied RV by 19% and in non-hypertrophied LV by 12% in comparison with normoxic controls. Chronically hypoxic hearts exhibited lower phospholipid n-6 polyunsaturated FA (PUFA) content mainly due to decreased linoleic acid (18:2n-6), which was opposed by increased n-3 PUFA mainly due to docosahexaenoic acid (22:6n-3) in phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI). The content of arachidonic acid (20:4n-6) was unchanged in total phospholipids, but in PC it was increased in both ventricles (by 22%) and in PE decreased in LV only (by 20%). Chronic hypoxia increased the un-saturation index of PC and PE in both ventricles. The content of monounsaturated FA (MUFA) was increased and 18:2n-6 decreased in DPG. The proportion of saturated FA was increased in PC and PI of hypoxic RV but not LV. The FA composition of phosphatidylserine was not altered in hypoxic ventricles. It is concluded that chronic hypoxia led to only minor changes in individual phospholipid concentration in rat ventricular myocardium, but markedly altered their FA profile. These changes, in particular the greater incorporation of n-3 PUFA into phospholipids and increased un-saturation index, may lead to a better preservation of membrane integrity and thereby contribute to improved ischemic tolerance of chronically hypoxic hearts.     

Chronic hypoxia induces right heart failure in caveolin-1-/- mice

Caveolin-1 (Cav-1)-/- mice develop mild pulmonary hypertension as they age. In this study, we sought to determine the effect of chronic hypoxia, an established model of pulmonary hypertension, on young Cav-1-/- mice with no measurable signs of pulmonary hypertension. Exposure of Cav-1-/- mice to chronic hypoxia resulted in an initial rise in right ventricular (RV) systolic pressure (RVSP) similar to wild-type (WT) mice. By three weeks RVSP decreased in the Cav-1-/- mice, whereas it was maintained in WT mice. The drop in RVSP in Cav-1-/- mice was accompanied by decreased cardiac output, increased RV hypertrophy, RV interstitial fibrosis, decreased RV sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a mRNA and decreased RV function compared with WT mice. Importantly, minimal differences were noted in pulmonary vascular remodeling between WT and Cav-1-/- mice, and left ventricular function was normal in hypoxic Cav-1-/- mice. Mechanistically, increased endothelial nitric oxide synthase uncoupling and increased tyrosine nitration of protein kinase G were detected in the RV of Cav-1-/- mice. These hemodynamic, histological, and molecular changes were prevented in Cav-1-/- mice expressing an endothelial-specific Cav-1 transgene or by nitric oxide synthase inhibition. These data suggest that, in Cav-1-/- mice, increased oxidative/nitrosative stress due to endothelial nitric oxide synthase uncoupling modifies the response of the RV to pressure overload, accelerating the deterioration of RV function.     

Lipid peroxidation in the myocardium in experimental infarct

Changes in the content of lipid peroxidation (LP) products and activities of antioxidant enzymes--superoxide dismutase, glutathione peroxidase and catalase in myocardium of rats after experimental infarction as well as after pretreatment with antioxidant ionol, beta-adrenoblocker inderal and verapamil, an inhibitor of slow Ca2+-channels have been studied. In the left ventricles of the control animals decreased levels of LP-products (Schiff bases and lipid hydroperoxides) have been registered as compared with right ventricles, accompanied by increased activity of antioxidant enzymes in the left ventricles. In experimental infarction the level of LP products increases and activity of antioxidant enzymes decreases both in ischemic and nonischemic regions of the heart. In nonischemic zone these changes can be prevented by pretreatment with inderal and ionol but not with verapamil.     

Exercise training alters the effect of chronic hypoxia on myocardial adrenergic and muscarinic receptor number.

Chronic hypoxic exposure results in elevated sympathetic activity leading to downregulation of myocardial alpha(1)- and beta-adrenoceptors (alpha(1)-AR, beta-AR). On the other hand, it has been shown that sympathetic activity is reduced by exercise training. The objective of this study was to determine whether exercise training could modify the changes in receptor expression associated with acclimatization. Four groups of rats were studied: normoxic sedentary rats (NS), rats living and training in normoxia (NTN), sedentary rats living in hypoxia (HS, inspired PO(2) = 110 Torr), and rats living and training in hypoxia (HTH, inspired PO(2) = 110 Torr). Training consisted of running in a treadmill at 80% of maximal O(2) uptake during 10 wk. Myocardial receptor density was measured by radioactive ligand binding. Right ventricular (RV) hypertrophy occurred in HS but not in HTH. No effect of exercise was detected in RV weight of normoxic rats. Acclimatization to hypoxia (HS vs. NS) resulted in a decrease in both alpha(1)- and beta-AR density, whereas muscarinic receptor (M-Ach) expression increased. Hypoxic exercise training (HS vs. HTH) moderated beta-AR downregulation and M-Ach upregulation and prevented the fall in alpha(1)-AR density. Normoxic training (NS vs. NTN) did not change beta-AR density. On the other hand, densities of alpha(1)-AR in both ventricles as well as RV M-Ach increased in NTN vs. NS. The data show that exercise training in hypoxia 1) prevents RV hypertrophy, 2) suppresses the downregulation of alpha(1)-AR in the left ventricle (LV) and RV, and 3) attenuates the changes in both beta-AR and M-Ach receptor density in LV and RV. Exercise training in normoxia increases M-Ach receptor expression in the RV.     

Assessment of caspase 3 activity in rabbit myocardial tissue during experimental hemodynamic overload of the left ventricle of the heart

It is well known that chronic overload of the cardiac left ventricle is accompanied by an increase in the cardiomyocyte apoptosis rate. However, direction and extent of changes in programmed cell death under an acute overload of the left ventricle still requires detailed investigation (as its pathogenesis significantly differs from chronic overload). Caspase-3 activity has been investigated in left ventricle myocardium of rabbits on days 1, 3, and 5 after modeling of left ventricle hemodynamic overload caused by experimental stenosis of the ascending aorta. Control group included intact animals. It was found that caspase-3 activity significantly increased in both ventricles on day 1; it increased more than twofold above control values on day 3 and decreased up to nearly control values on day 5. Based on these data it was concluded that the acute hemodynamic overload of the left ventricle may be a cause of increased apoptosis in the myocardial tissue of both cardiac ventricles during first days of the pathological process.     

Enhanced ROS production by NADPH oxidase is correlated to changes in antioxidant enzyme activity in human heart failure

In pathological conditions, the balance between reactive oxygen species (ROS) and antioxidants may shift toward a relative increase of ROS, resulting in oxidative stress. Conflicting data are available on antioxidant defenses in human failing heart and they are limited to the left ventricle. Thus, we aimed to investigate and compare the source of oxidant and antioxidant enzyme activities in the right (RV) and left (LV) ventricles of human failing hearts. We found a significant increase in superoxide production only by NADPH oxidase in both failing ventricles, more marked in RV. Despite unchanged mRNA or protein expression, catalase (CAT) and glutathione peroxidase (GPx) activities were increased, and their increases reflected the levels of Tyr phosphorylation of the respective enzyme. Manganese superoxide dismutase (Mn-SOD) activity appeared unchanged. The increase in NADPH oxidase-dependent superoxide production positively correlated with the activation of both CAT and GPx. However, the slope of the linear correlation (m) was steeper in LV than in RV for GPx (LV: m = 2.416; RV: m = 1.485) and CAT (LV: m = 1.007; RV: m = 0.354). Accordingly, malondialdehyde levels, an indirect index of oxidative stress, were significantly higher in the RV than LV. We conclude that in human failing RV and LV, oxidative stress is associated with activation of antioxidant enzyme activity. This activation is likely due to post-translational modifications and more evident in LV. Overall, these findings suggest a reduced protection of RV against oxidative stress and its potential contribution to the progression toward overt heart failure.     

In Vivo Human Left-to-Right Ventricular Differences in Rate Adaptation Transiently Increase Pro-Arrhythmic Risk following Rate Acceleration

Left-to-right ventricular (LV/RV) differences in repolarization have been implicated in lethal arrhythmias in animal models. Our goal is to quantify LV/RV differences in action potential duration (APD) and APD rate adaptation and their contribution to arrhythmogenic substrates in the in vivo human heart using combined in vivo and in silico studies. Electrograms were acquired from 10 LV and 10 RV endocardial sites in 15 patients with normal ventricles. APD and APD adaptation were measured during an increase in heart rate. Analysis of in vivo electrograms revealed longer APD in LV than RV (207.8±21.5 vs 196.7±20.1 ms; P<0.05), and slower APD adaptation in LV than RV (time constant τ^s = 47.0±14.3 vs 35.6±6.5 s; P<0.05). Following rate acceleration, LV/RV APD dispersion experienced an increase of up to 91% in 12 patients, showing a strong correlation (r² = 0.90) with both initial dispersion and LV/RV difference in slow adaptation. Pro-arrhythmic implications of measured LV/RV functional differences were studied using in silico simulations. Results show that LV/RV APD and APD adaptation heterogeneities promote unidirectional block following rate acceleration, albeit being insufficient for establishment of reentry in normal hearts. However, in the presence of an ischemic region at the LV/RV junction, LV/RV heterogeneity in APD and APD rate adaptation promotes reentrant activity and its degeneration into fibrillatory activity. Our results suggest that LV/RV heterogeneities in APD adaptation cause a transient increase in APD dispersion in the human ventricles following rate acceleration, which promotes unidirectional block and wave-break at the LV/RV junction, and may potentiate the arrhythmogenic substrate, particularly in patients with ischemic heart disease.     

Identification of new biophysical markers for pathological ventricular remodelling in tachycardia‐induced dilated cardiomyopathy

Our aim was to identify biophysical biomarkers of ventricular remodelling in tachycardia‐induced dilated cardiomyopathy (DCM). Our study includes healthy controls (N = 7) and DCM pigs (N = 10). Molecular analysis showed global myocardial metabolic abnormalities, some of them related to myocardial hibernation in failing hearts, supporting the translationality of our model to study cardiac remodelling in dilated cardiomyopathy. Histological analysis showed unorganized and agglomerated collagen accumulation in the dilated ventricles and a higher percentage of fibrosis in the right (RV) than in the left (LV) ventricle (P = .016). The Fourier Transform Infrared Spectroscopy (FTIR) 1st and 2nd indicators, which are markers of the myofiber/collagen ratio, were reduced in dilated hearts, with the 1st indicator reduced by 45% and 53% in the RV and LV, respectively, and the 2nd indicator reduced by 25% in the RV. The 3rd FTIR indicator, a marker of the carbohydrate/lipid ratio, was up‐regulated in the right and left dilated ventricles but to a greater extent in the RV (2.60‐fold vs 1.61‐fold, P = .049). Differential scanning calorimetry (DSC) showed a depression of the freezable water melting point in DCM ventricles – indicating structural changes in the tissue architecture – and lower protein stability. Our results suggest that the 1st, 2nd and 3rd FTIR indicators are useful markers of cardiac remodelling. Moreover, the 2nd and 3rd FITR indicators, which are altered to a greater extent in the right ventricle, are associated with greater fibrosis.