bluuebunny/crossref_metadata_2025 huggingface dataset:
Accelerated thrombolysis and reperfusion in a canine model of myocardial infarction by liposomal encapsulation of streptokinase.
Authors: Nguyen P D , O'Rear E A , Johnson A E , Patterson E , Whitsett T L , Bhakta R
Published: June 2012

The aim of thrombolytic therapy for acute myocardial infarction with plasminogen activators such as streptokinase is to lyse the coronary thrombus and reestablish blood flow as quickly as possible so that heart tissue loss is minimized and mortality rates are improved. Streptokinase has been encapsulated in large unilamellar phospholipid vesicles and tested in an animal model of acute myocardial infarction. The time required to restore vessel patency has been reduced more than 50% when compared with findings for free streptokinase. The total dosage of streptokinase required was lower, and smaller remnant thrombi were observed with the encapsulated agent. Results from this initial unoptimized study may have significant implications for further reduction in mortality from heart attacks by therapy with plasminogen activators.
Noninvasive recovery of epicardial potentials in a realistic heart-torso geometry. Normal sinus rhythm.
Authors: Messinger-Rapport B J , Rudy Y
Published: June 2012

The inverse problem in electrocardiography implies the reconstruction of electrical events within the heart from information measured noninvasively on the body surface. Deduction of these electrical events is possible from measured epicardial potentials, and, thus, a noninvasive method of recovering epicardial potentials from body surface data is useful in experimental and clinical studies. In the present study, an inverse method that uses Tikhonov regularization was shown to reconstruct, with good accuracy, important events in cardiac excitation. The inverse procedure was employed on data obtained from a human-torso tank in which a beating canine heart was placed in the correct anatomical position. Comparison with the actual, measured epicardial potentials indicates that positions and shapes of potential features (maxima, minima, zero potential line, saddles, etc.) are recovered with good accuracy throughout the QRS. An error in position of up to 1 cm is typical, while amplitudes are slightly diminished. In addition, application was extended from the above setting, in which the geometry was precisely known and potentials at a large number of leads were measured accurately, to a situation that is more representative of clinical and experimental settings. Effects of inaccuracy in location of the position of the heart were examined. A stylized torso that approximates the actual geometry was designed, and its performance in the inverse computations was evaluated. A systematic method of reduction of the number of leads on the body surface was proposed, and the resulting lead configurations were evaluated in terms of the accuracy of inverse solutions. The results indicate that the inverse problem can be stabilized with respect to different types of uncertainties in measured data and offer promise in the use of the inverse procedure in clinical and experimental situations.
Flow patterns and spatial distribution of atherosclerotic lesions in human coronary arteries.
Authors: Asakura T , Karino T
Published: June 2012

To investigate the potential role of fluid mechanical factors in the localized genesis and development of atherosclerotic lesions in humans, the exact anatomic locations of atherosclerotic lesions and the flow patterns at such sites in left and right human coronary arteries were studied in detail by flow visualization and high-speed cinemicrographic techniques using five isolated, transparent human coronary arterial trees prepared postmortem. It was found that atherosclerotic plaques and wall thickenings in left and right coronary arteries were localized almost exclusively on the outer wall of one or both daughter vessels at major bifurcations and T-junctions, which left the flow-divider free of lesions, and along the inner wall of curved segments. When flow patterns in such vessels were studied in detail, it was discovered that these sites were where flow was either slow or disturbed with the formation of slow recirculation and secondary flows and where wall shear stress was low. The results indicate that the major hemodynamic factors directly related to the localization of atherosclerotic plaques and wall thickenings in the human arterial system are the low fluid velocity and the resultant low shear stress that acts on the vessel wall.
Local response to cardiac overload on myosin heavy chain gene expression and isozyme transition.
Authors: Imamura S , Matsuoka R , Hiratsuka E , Kimura M , Nishikawa T , Takao A
Published: June 2012

It is uncertain whether the shift of cardiac myosin heavy chain (MHC) during pressure overload can be induced by some intrinsic factors or by the stress imposed directly on the individual myocytes. To study whether the changes in cardiac MHC gene expression produced by one-sided overload are limited to the involved ventricle or extend to the other ventricle, we examined MHC gene expression and isozyme transition in the left and right ventricles in aortic coarctated and pulmonary artery-banded rats. It has been confirmed that the pressure overload is indeed limited to the loaded ventricle. The results showed that, compared with sham-operated rats, there was no significant induction of the beta-MHC messenger RNA and corresponding protein in the unloaded ventricle, whereas significant induction was observed in the overloaded ventricle. These results demonstrated that the changes in MHC gene expression and isozyme produced by one-sided ventricular overload are limited to the involved ventricle. We conclude that the MHC gene regulation during hemodynamic overload may not be induced by intrinsic factors, such as hormones, catecholamine, or atrial natriuretic peptide, but is induced by direct local response to increased load.
Gap junction messenger RNA expression by vascular wall cells.
Authors: Larson D M , Haudenschild C C , Beyer E C
Published: June 2012

Gap junctions between vessel wall cells provide a pathway for the intercellular exchange of ions and small molecules. Pure cultures of microvascular and macrovascular endothelial and smooth muscle cells, vascular pericytes, and several nonvascular cell lines were tested for junctional communication by fluorescent dye transfer. All of the vascular wall cells were capable of dye transfer. Since gap junctions are formed by a family of related proteins (connexins) whose unique domains may confer physiological regulatory properties, we tested total RNA from these cultures by Northern blot analysis for expression of the currently available, characterized, and cloned mammalian gap junction proteins: connexin26, connexin32, and connexin43. All of the vascular wall cells expressed connexin43 messenger RNA. Connexin43 was expressed in vascular cells from bovine, porcine, rat, and human sources. Several nonvascular cell lines of mesenchymal origin also expressed connexin43 messenger RNA. When high stringency Northern blots were used, messenger RNAs for connexin32 or connexin26 were not detected in any of the vascular wall cells but were expressed in several cell lines of epithelial origin. Freshly isolated and purified aortic endothelial and smooth muscle RNA preparations similarly contained only connexin43 messenger RNA, excluding the possibility of culture-induced alterations in gene expression. The expression of connexin43 by all vascular wall cells may provide a mechanism for the functional integration of the vessel wall by gap junctions.
Phorbol ester and dioctanoylglycerol stimulate membrane association of protein kinase C and have a negative inotropic effect mediated by changes in cytosolic Ca2+ in adult rat cardiac myocytes.
Authors: Capogrossi M C , Kaku T , Filburn C R , Pelto D J , Hansford R G , Spurgeon H A , Lakatta E G
Published: June 2012

We used left ventricular myocytes from adult rats to investigate the effect of 4 beta-phorbol 12-myristate 13-acetate (PMA) and of sn-1,2-dioctanoylglycerol (DiC-8) on the membrane association of protein kinase C (PKC), cytosolic [Ca2+], (Cai) homeostasis, and the contractile properties of single cardiac cells. Because PKC activity is known to be highly Ca2+ sensitive, the K+ concentration of the bathing medium was raised from 5 to 30 mM in some experiments, a perturbation known to depolarize the cell and increase Cai. In cell suspensions both PMA (3 x 10(-10) and 3 x 10(-7) M) and DiC-8 (10(-5) and 10(-4) M) increased membrane association of PKC. The effect of PMA (10(-7) M) on PKC translocation was enhanced in 30 mM KCl compared with 5 mM KCl. During steady field stimulation at 1 Hz in 1 mM bathing [Ca2+], both PMA (10(-7) M) and DiC-8 (10(-5) M) decreased twitch amplitude to approximately 60% of control in 5 mM KCl, and the negative inotropic effect of either drug was more pronounced in 30 mM KCl than in 5 mM KCl. In single cardiac myocytes loaded with the Ca2+ indicator indo-1 and bathed in 5 mM KCl, we simultaneously measured cell length and Cai. The myofilament responsiveness to Ca2+ was assessed by the relation between contraction amplitude and the peak of the Cai transient. The negative inotropic effect of both PMA and DiC-8 was related to a diminished amplitude of the Cai transient and not to a decreased myofilament responsiveness to Ca2+. In the absence of electrical stimulation, PMA (10(-7) M) and DiC-8 (10(-5) M) decreased the frequency of contractile waves due to spontaneous Ca2+ release from the sarcoplasmic reticulum, and DiC-8 also decreased resting Cai. Thus, activation of PKC, which is thought to occur as part of the response of cardiac muscle to alpha 1-adrenergic stimulation, is associated with a negative inotropic action due to a smaller Cai transient rather than to a decrease in the myofilament responsiveness to Ca2+. These effects on the membrane association of PKC and on contractility are enhanced by cell depolarization achieved by raising [KCl] in the bathing medium.
Immunohistochemical demonstration of human cardiac innervation before and after transplantation.
Authors: Wharton J , Polak J M , Gordon L , Banner N R , Springall D R , Rose M , Khagani A , Wallwork J , Yacoub M H
Published: June 2012

Knowledge about the distribution and origins of peptide-containing nerves in the innervated and transplanted heart is lacking. Immunohistochemical and histochemical techniques were used to visualize human cardiac innervation before and after transplantation. In the recipient heart cardiac nerve fibers and fascicles displayed immunoreactivity for general neural (protein gene product 9.5 and synaptophysin) and Schwann cell markers (S-100). A major proportion of cardiac nerves displayed neuropeptide tyrosine and tyrosine hydroxylase immunofluorescence staining. Subpopulations of nerves contained somatostatin, vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P- or neurokinin-like immunoreactivity, and acetylcholinesterase activity. Tissues from cardiac allografts (5 weeks to 63 months after transplantation) contained nerves and ganglion cells that were acetylcholinesterase positive and immunoreactive for the general neural markers. These nerves were less numerous than in recipient hearts and rarely displayed neuropeptide immunostaining. Atrial natriuretic peptide immunoreactivity was localized to myocardial cells in transplanted hearts as well as explanted recipient and postmortem hearts. While most human cardiac allografts remain functionally extrinsically denervated, they appear to contain viable intrinsic nerves, and myocardial cells retain the capacity to produce atrial natriuretic peptide.
Conduction disturbances caused by high current density electric fields.
Authors: Yabe S , Smith W M , Daubert J P , Wolf P D , Rollins D L , Ideker R E
Published: June 2012

During internal defibrillation, potential gradients greater than 100 V/cm occur near defibrillation electrodes. Such strong fields may cause deleterious effects, including arrhythmias. This study determined 1) the effects of such strong fields on the propagation of activation and 2) whether these effects were different for monophasic and biphasic shocks. Voltages and potential gradients during the shock, as well as activation sequences before and after the shock, were mapped from 117 epicardial electrodes placed over a 3 x 3-cm area on the right ventricle in six dogs. Pacing at a cycle length of 350 msec was given from a long narrow electrode on the right side of the mapped area to generate parallel activation isochrones. A monophasic shock, 10 msec in duration, or a biphasic shock with both phases 5 msec in duration was delivered 300 msec after the last paced stimulus via a mesh electrode on the left side of the mapped area as the cathode, with the anode on the right atrium. Shocks of 70-850 V were given, and the potential gradient and current density at each recording electrode were calculated from the measured potentials and fiber orientation by using a finite element method. Pacing was resumed 200 msec after the shock, and activation sequences were mapped for up to 5 minutes. Potential gradients ranged from 1 to 189 V/cm with high fields on the left side and low fields on the right side of the mapped area. Where the potential gradient was weak, the first activation sequence after the shock was similar to that before the shock, but activation blocked without conducting into areas where the gradient was greater than 64 +/- 4 (mean +/- SD) V/cm for monophasic and greater than 71 +/- 6 V/cm for biphasic shocks. These values are significantly different (p less than 0.003). The higher the potential gradient, the longer was the duration of block before conduction returned. Block duration, however, was generally shorter for biphasic than for monophasic waveforms of the same field strength. In conclusion, conduction block can follow either waveform, but biphasic waveforms cause less block than monophasic waveforms. This effect may partially explain the increased defibrillation efficacy of biphasic shocks.
Oxidized low density lipoproteins potentiate vasoconstrictions to various agonists by direct interaction with vascular smooth muscle.
Authors: Galle J , Bassenge E , Busse R
Published: June 2012

In hypercholesterolemia, low density lipoproteins (LDLs) may be oxidized by monocytes/macrophages in the arterial wall. Therefore, we investigated the effect of LDL and its oxidative derivatives (ox-LDL) on vascular tone in isolated perfused rabbit femoral arteries. Perfusion of endothelium-intact and endothelium-denuded segments with ox-LDL (80 micrograms protein/ml) caused no or only weak vasoconstrictions in the absence of contractile agonists. However, in the presence of ox-LDL, vasoconstrictions to threshold concentrations of norepinephrine, serotonin, phenylephrine, or potassium were significantly enhanced. This enhancement correlated with the degree of oxidation. When ox-LDL was administered at higher concentrations (greater than 200 micrograms protein/ml), it evoked moderate vasoconstrictions even in the absence of contractile agonists. Native LDL had no effect on vascular tone. Preincubation with verapamil, diltiazem, and nitrendipine inhibited vasoconstrictions evoked by ox-LDL, both in the presence and in the absence of a contractile agonist. The contractile responses to ox-LDL were significantly greater in endothelium-denuded segments than in endothelium-intact segments. At the above concentrations, ox-LDL had no influence on endothelium-derived relaxing factor-mediated vasodilations. These data indicate that ox-LDL enhances agonist-induced vasoconstrictions by a direct effect on the vascular smooth muscle. We therefore suggest that ox-LDL is an important factor that may increase the risk of inappropriate vasoconstriction in hypercholesterolemia, independent of its putative cytotoxic effect on the endothelium.
Muscle length, shortening, myoplasmic [Ca2+], and activation of arterial smooth muscle.
Authors: Rembold C M , Murphy R A
Published: June 2012

The effect of muscle length on smooth muscle contraction was evaluated by measuring myoplasmic [Ca2+] (with aequorin), myosin light chain phosphorylation, length, and isometric stress in histamine-stimulated swine carotid media preparations. Tissues were equilibrated at the optimal length for stress development (Lo). Isometric contractions at short tissue lengths (0.7 Lo) were associated with a decrease in maximal stress development. Isometric contraction at 0.7 Lo also reduced the sensitivity to histamine as measured by steady-state increases in [Ca2+], phosphorylation, or stress. This suggests that decreased agonist sensitivity at shorter lengths is caused by reduced Ca2+ mobilization. Isotonic shortening also led to decreases in histamine sensitivity. Isometric contractions at 1.2 Lo were not associated with significant changes in histamine-induced increases in [Ca2+]. The [Ca2+] dependence of phosphorylation was not altered at 0.7 or 1.2 Lo. Sinusoidal length changes from 0.95 to 1.05 Lo at 1 Hz were not associated with significant changes in the resting or histamine-stimulated [Ca2+]. These results suggest that Ca2+ mobilization and the resulting contraction is relatively independent of length changes near Lo. Inactivation occurs at lengths substantially below Lo where Ca2+ mobilization by agonists is impaired.
5-Hydroxytryptamine induces phospholipase C-mediated hydrolysis of phosphoinositides through 5-hydroxytryptamine-2 receptors in cultured fetal mouse ventricular myocytes.
Authors: Hamamori Y , Yokoyama M , Yamada M , Akita H , Goshima K , Fukuzaki H
Published: June 2012

5-Hydroxytryptamine (5-HT) stimulates the rate and force of cardiac contraction. However, the molecular mechanisms of 5-HT actions on the heart are unknown. We examined effects of 5-HT on phospholipase C-mediated hydrolysis of phosphoinositides and its regulation in cultured fetal mouse ventricular myocytes labeled with [3H]inositol. Accumulation of inositol monophosphate, inositol bisphosphate, and inositol trisphosphate was assessed after stimulation with 5-HT, catecholamines, and AlF4-. Inositol bisphosphate and trisphosphate reached a peak at 15 minutes by 5-HT stimulation and at 30 minutes by AlF4- stimulation. Inositol monophosphate accumulated linearly for at least 30 minutes in the presence of LiCl. The 5-HT effect was dose dependent, and the threshold concentration was 0.1 microM with the half-maximum effective concentration of 1 microM. Ketanserin in nanomolar concentrations inhibited the phospholipase C reaction by 100 microM 5-HT with the half-maximum inhibitory concentration of 0.5 nM. Pertussis toxin (100-1,000 ng/ml) did not influence the phospholipase C reaction by 5-HT, but it partially inhibited the reaction by AlF4-. Protein kinase C-activating phorbol esters like 12-O-tetradecanoylphorbol 13-acetate (TPA) and phorbol 12,13-dibutyrate, but not 4 alpha-phorbol 12,13-didecanoate, which is inactive for protein kinase C, completely inhibited the reaction by 5-HT; TPA showed 30% inhibition on the reaction by AlF4-. The magnitude of accumulated inositol phosphates by AlF4- was at least several times greater than that by 5-HT. Norepinephrine- and epinephrine-stimulated phospholipase C reactions were completely abolished by prazosin. These results suggest that 5-HT directly stimulates phospholipase C-mediated hydrolysis of phosphoinositides through 5-hydroxytryptamine-2 (5-HT2) receptors in the ventricular myocytes and that this reaction is negatively regulated by protein kinase C. 5-HT2 receptors may be coupled to phospholipase C via a pertussis toxin-insensitive GTP-binding protein in the myocytes.
Control of coronary vascular tone by nitric oxide.
Authors: Kelm M , Schrader J
Published: June 2012

A specific difference-spectrophotometric method was used to measure nitric oxide (NO) release into the coronary effluent perfusate of isolated, constant-flow-perfused guinea pig hearts. Authentic NO applied into the coronary circulation decreased vascular resistance dose dependently and enhanced coronary release of cyclic GMP (cGMP) fivefold. Increasing oxygen tension in aqueous solutions from 150 to 700 mm Hg decreased NO half-life (5.6 seconds) by 32%. During single passage through the intact coronary system, 86% of the infused NO was converted to nitrite ions. Oxidation of NO was more than 30 times faster within the heart than in aqueous solution. Endogenously formed NO was constantly released into the coronary effluent perfusate at a rate of 161 +/- 11 pmol/min. The NO scavenger oxyhemoglobin and methylene blue increased coronary resistance and decreased cGMP release (basal release, 342 +/- 4 fmol/min), whereas superoxide dismutase reduced coronary resistance. L-Arginine (10(-5) M) slightly decreased coronary perfusion pressure and enhanced release of cGMP. NG-Monomethyl L-arginine (10(-4) M) reduced basal release of NO and cGMP by 26% and 31%, respectively, paralleled by a coronary vasoconstriction. Bradykinin in the physiological range from 5 x 10(-11) M to 10(-7) M dilated coronary resistance vessels, which was paralleled by the release of NO and cGMP. Onset of NO release preceded onset of coronary vasodilation in all cases. Upon stimulation with bradykinin, amounts of endogenously formed NO were within the same range as the dose-response curves for exogenously applied NO both for changes in coronary resistance and cGMP release. Acetylcholine (10(-5) M), ATP (10(-5) M), and serotonin (10(-8) M) increased the rate of NO and cGMP release, resulting in coronary vasodilation. Our data suggest the following: 1) NO, the most rapidly acting vasodilator presently known, is metabolized within the heart mainly to nitrite and exhibits a half-life of only 0.1 second; 2) in the unstimulated heart, basal formation of NO may play an important role in setting the resting tone of coronary resistance vessels; 3) the kinetics and quantities of NO formation suggest that NO is causally involved in the bradykinin-induced coronary vasodilation; and 4) amounts of NO formed within the heart stimulated with ATP, acetylcholine, and serotonin are effective for vasodilation.
Role of endothelium-derived relaxing factor and prostaglandins in responses of coronary arteries to thromboxane in vivo.
Authors: Szwajkun K , Lamping K G , Dole W P
Published: June 2012

We examined the relative contribution of endothelial and vascular smooth muscle-derived prostaglandins and endothelium-derived relaxing factor in modulating both the large coronary artery and resistance vessel responses to thromboxane in vivo. Vascular responses to the thromboxane analogue U46619 were measured in four separate experimental protocols: 1) The vascular responses were measured in the presence and absence of intact endothelium to examine the role of endothelium-derived vasodilators. 2) Responses were measured in the presence of intact endothelium before and after inhibition of cyclooxygenase with indomethacin to examine the role of endothelial and vascular smooth muscle-derived prostaglandins. 3) Responses were measured after endothelial removal before and after indomethacin to examine the role of vascular smooth muscle-derived prostaglandins. 4) Responses were measured after indomethacin and before and after removal of endothelium to examine the role of endothelium-derived relaxing factor. In anesthetized dogs (n = 41) that underwent constant pressure perfusion of the left anterior descending coronary artery (LAD), LAD diameter was measured with sonomicrometer crystals, and coronary flow was measured with an electromagnetic flow probe. Intracoronary infusion of U46619 (0.01-1.0 microgram/min) produced a dose-dependent constriction of LAD. Constriction of the LAD was augmented after endothelial removal, after indomethacin treatment in both the presence and absence of endothelium, and after removal of the endothelium in the presence of indomethacin. Inhibition of prostaglandin synthesis had the greatest effect of augmenting constriction of LAD to thromboxane. Coronary flow was decreased by U46619 only in the presence of indomethacin.(ABSTRACT TRUNCATED AT 250 WORDS)
Induction of insulin-like growth factor I messenger RNA in rat aorta after balloon denudation.
Authors: Cercek B , Fishbein M C , Forrester J S , Helfant R H , Fagin J A
Published: June 2012

Insulin-like growth factor I (IGF-I) is a widely distributed mitogen that mediates the growth-promoting effects of platelet-derived growth factor in mesenchymal cells. We show that rat aortic IGF-I messenger RNA (mRNA) is induced 24 hours after deendothelialization, at a time when smooth muscle cell proliferation within the intima is still not apparent. After 7 days, IGF-I mRNA induction peaks at about ninefold control levels and then falls to about threefold 14 days after denudation when smooth muscle cell proliferation is at its peak. We also show that, of the 5' untranslated IGF-I mRNA transcripts, only the class C transcript is expressed and regulated in aortic tissue. In contrast, treatment of rats with supraphysiological doses of growth hormone, the major endocrine regulator of IGF-I gene expression, elicited only twofold induction of aortic IGF-I mRNA. Our findings suggest that IGF-I may be an important autocrine or paracrine regulator of smooth muscle cell proliferation and that it may be significant in determining the cellular response to arterial wall injury.
Influence of lung volume on sympathetic nerve discharge in normal humans.
Authors: Seals D R , Suwarno N O , Dempsey J A
Published: June 2012

The purpose of this study was to determine the influence of tidal volume, breathing pattern, and beginning lung volume on the modulation of efferent, muscle sympathetic nerve activity (MSNA) in humans. In seven supine, healthy subjects, we measured MSNA (microneurography of the right peroneal nerve) and beat to beat arterial blood pressure during 1) low-frequency breathing (fb = 12 breaths/min) at tidal volumes (VT) of 30% (control), 50%, and 70% of inspiratory capacity and with inspiratory time-to-total breath time ratios (TI/TTOT) of 0.3-0.5 (control), less than 0.3, and greater than 0.5; and 2) simulated exercise hyperpnea (fb = 40 breaths/min; VT = 60-70% inspiratory capacity; minute ventilation, approximately 90 1). To optimize our ability to discern modulatory effects, breathing was performed during three conditions of heightened MSNA: nonhypotensive (less than 20 mm Hg) lower-body negative pressure, isometric handgrip exercise, and posthandgrip vascular occlusion (ischemia). PETCO2 was maintained at normal levels by adjusting the FICO2. Within-breath modulation of MSNA was observed during control tidal breathing with approximately 65% of the burst frequency occurring during the expiratory phase. Deep, low-frequency breathing potentiated this modulatory influence (p less than 0.05 versus control) and produced near-complete sympathoinhibition from onset-mid inspiration to early-mid expiration. Increasing (slow inspiration) and decreasing (fast inspiration) TI/TTOT shifted the onset of sympathoinhibition occurring later (greater change in volume) and earlier (less change in volume) during inspiration, respectively. In two subjects who performed deep breathing from an elevated beginning lung volume, the sympathoinhibition was observed earlier in the inspiratory period and with less change in volume compared with control. These within-breath modulatory effects did not appear to be due solely to changes in arterial pressure. Sustained low- or high ("exerciselike")-frequency deep breathing did not alter total minute MSNA compared with control breathing. These results demonstrate that the depth and pattern of breathing, and possibly the starting lung volume, exert marked influences on the within-breath modulation of MSNA in humans. Our findings also suggest that these modulatory effects may be mediated, at least in part, by pulmonary stretch reflexes.
Effect of amiodarone on the expression of myosin isoforms and cellular growth of cardiac muscle cells in culture.
Authors: Nag A C , Lee M L , Shepard D
Published: June 2012

The effect of amiodarone on the expression of myosin isoforms and the growth of neonatal rat cardiac muscle cells in culture was studied by native gel electrophoresis, assays of DNA and protein synthesis, and electron microscopy. Cardiac myocytes exposed to amiodarone in the absence of triiodothyronine (T3) showed predominant V1. When cardiac myocytes were exposed to amiodarone in the presence of T3, they expressed prevalent isomyosin V3, or both V3 and V1 equally. Supraphysiological concentration of T3 counteracted the effect of amiodarone on myocytes, showing the expression of predominant isomyosin V1. Amiodarone has inhibitory effects on DNA synthesis and differentiation of cardiac myocytes. Myocytes treated with amiodarone showed maximum labeling index with 11% labeled cells after day 1. Subsequently, the labeling indexes declined and on the third day ceased, as opposed to the control culture, which attained a peak in labeling index with 60% labeled myocytes on the third day. The labeling indexes declined, showing 11% labeled myocytes at the terminal time point. Myocytes treated with amiodarone lost most of the well-organized myofibrils and other organelles, and instead contained sparse, scattered segments of myofibrils, free myofilaments, many mitochondria with disrupted cristae, and autophagic vacuoles. The results demonstrated that amiodarone has a direct influence on the expression of isomyosin by cardiac myocytes. Furthermore, this drug has inhibitory and degrading effects on the growth and differentiation of cardiac myocytes.
The effects of increasing mean arterial pressure on left ventricular output in newborn lambs.
Authors: Van Hare G F , Hawkins J A , Schmidt K G , Rudolph A M
Published: June 2012

We developed a preparation in which the mean arterial pressure of the newborn lamb is varied with little change in left ventricular preload. Seven lambs underwent balloon atrial septostomy and were instrumented with vascular catheters, an electromagnetic flow transducer on the aorta, and a balloon occluder on the aorta. Four different preload conditions were established by volume infusion or withdrawal. Aortic flow was measured continuously during gradual occlusion of the aorta. Curves relating mean left atrial pressure to stroke volume before balloon inflation showed a plateau, with little increase in stroke volume with increases in atrial pressure above 7 mm Hg. With balloon inflation, stroke volume decreased linearly with increases in mean arterial pressure. Curves relating left atrial pressure to stroke volume constructed at constant mean atrial pressure showed no plateau but showed continued increases in stroke volume as left atrial pressure was increased to 10 mmHg. When mean arterial pressure is constant, the Starling mechanism is operative in newborn left ventricles. The plateau in newborn lamb function curves is due to increases in mean arterial pressure that accompany volume infusion.
Acute impairment of endothelium-dependent relaxations to aggregating platelets following reperfusion injury in canine coronary arteries.
Authors: Pearson P J , Schaff H V , Vanhoutte P M
Published: June 2012

Experiments were designed to determine whether endothelial injury contributes to augmented coronary vascular tone seen during myocardial reperfusion. Canine left anterior descending coronary arteries were exposed to ischemia followed by reperfusion (60 minutes each). Rings (3-4 mm) of the reperfused artery and of normal left circumflex (control) coronary artery segments were prepared. Rings were suspended for isometric force measurement in organ chambers containing modified Krebs' Ringer bicarbonate solution (37 degrees C, 95% O2-5% CO2). Endothelium-independent contractions to KCl and prostaglandin F2 alpha were unaltered after reperfusion. Endothelium-dependent relaxations to nitric oxide, sodium nitroprusside, and isoproterenol were comparable in control and reperfused arteries. However, reperfused coronary arteries contracted with prostaglandin F2 alpha lost the ability to express endothelium-dependent relaxations to aggregating platelets. Reperfused arterial rings also exhibited impaired endothelium-dependent relaxations to acetylcholine, the calcium ionophore A23187, and the platelet-derived compounds ADP and serotonin. Quiescent (noncontracted) reperfused arterial rings exhibited larger contractions than controls when exposed to aggregating platelets. In such quiescent rings, the endothelium-dependent increase in tension to hemoglobin was unaltered after reperfusion. Thus, coronary reperfusion impairs the normal endothelium-dependent relaxations to aggregating platelets and vasoactive drugs. This impairment of platelet-mediated coronary relaxation could help explain the increased vascular tone and tendency toward vasospasm commonly observed after reperfusion of the coronary arteries.
Contribution of endothelial cells to calcium-dependent fluorescence transients in rabbit hearts loaded with indo 1.
Authors: Lorell B H , Apstein C S , Cunningham M J , Schoen F J , Weinberg E O , Peeters G A , Barry W H
Published: June 2012

In studies that attempt to measure intracellular calcium [( Ca2+]i) in the intact heart with the calcium indicator indo 1-AM, a fundamental assumption is that the signals report changes in myocyte [Ca2+]i. We studied isolated perfused rabbit hearts loaded with the calcium probe indo 1-AM and recorded surface fluorescence of the left ventricle during continuous excitation at 360 nm. In cells containing indo 1, an increase in [Ca2+]i is associated with an increase in fluorescence intensity at 400 nm, a decrease in intensity at 500 nm, and an increase in the 400:500 nm ratio. Beat-to-beat fluorescence transients were recorded from the surface of the heart coincident with contraction, indicating that a component of the fluorescence signals is derived from beating myocytes. To evaluate the potential contribution of endothelial cells, we compared the response to increases in [Ca2+]o or bradykinin (10(-5) M). In response to an increase of the [Ca2+] in the perfusate from 0.6 to 3.0 mM, left ventricular developed pressure and +dP/dt increased with a simultaneous increase in the [Ca2+]i-sensitive 400:500 nm ratio. Perfusion with the endothelial cell agonist bradykinin caused no change in left ventricular isovolumic peak systolic pressure or left ventricular dP/dt, whereas bradykinin evoked an immediate elevation in both the diastolic and systolic levels of the [Ca2+]i-sensitive 400:500 nm ratio. In additional experiments with indo 1-loaded isolated beating myocytes, superfusion with bradykinin had no effect on either the fluorescence [Ca2+]i transients or contractility. In contrast, superfusion of indo 1-loaded cultured endothelial cells with bradykinin caused the elevation of [Ca2+]i within seconds. Fluorescence microscopy of unstained frozen tissue sections from indo 1-loaded hearts also suggested the presence of more intense microvascular endothelial cell indo 1 fluorescence relative to that observed in myocytes. These experiments provide evidence that a component of [Ca2+]i-sensitive fluorescence of whole hearts loaded with indo 1 is contributed by nonmyocyte sources, including endothelial cells. These results also raise the caution that the abrupt rise of [Ca2+]i that has been observed during the initial phase of ischemia in whole hearts loaded with indo 1 may be partly derived from endothelial cells rather than myocytes.
Prostaglandins mediate arteriolar dilation to increased blood flow velocity in skeletal muscle microcirculation.
Authors: Koller A , Kaley G
Published: June 2012

In cremaster muscle of pentobarbital-anesthetized rats, temporary occlusion of an arteriole increased red blood cell velocity (mean increase, 8.2 +/- 1.0 mm/sec from a control velocity of 7.9 +/- 0.7 mm/sec) in proximal parallel arteriolar branches (mean control diameter, 19.4 +/- 0.6 microns). Increases in flow velocity were consistently followed by proportional delayed (6-15 seconds) increases in arteriolar diameter (5.8 +/- 0.7 microns). Administration of NG-monomethyl-L-arginine (200 microM), an inhibitor of the synthesis of endothelium-derived relaxing factor that blocked the arteriolar responses to acetylcholine (1 microM) but not to arachidonic acid (10 microM), did not affect the dilation (mean increase, 8.9 +/- 1.1 microns) due to increases in red blood cell velocity (13.4 +/- 1.5 mm/sec). However, the cyclooxygenase inhibitor indomethacin (or meclofenamate), which completely blocked the dilator response to arachidonic acid but did not change the response to acetylcholine, inhibited the arteriolar dilation (mean increase, 0.3 +/- 0.2 micron) due to increases in red blood cell velocity (9.3 +/- 1.0 mm/sec). Inhibition of prostaglandin synthesis also reduced the increase in calculated blood flow by 57% during occlusion. These results suggest that the arterioles are sensitive to increases in blood flow velocity (wall shear stress), in response to which they release prostaglandins, eliciting vasodilation. The existence of this phenomenon in the skeletal muscle microcirculation suggests a new regulatory mechanism that, by modulation of vascular resistance in the microvascular network, has the role of normalizing wall shear stress and providing for substantial increases in tissue blood flow.
Oxidative stress alters specific membrane currents in isolated cardiac myocytes.
Authors: Bhatnagar A , Srivastava S K , Szabo G
Published: June 2012

To evaluate the effects of oxidative stress on cardiac membrane currents, single cells from frog ventricle were exposed to tert-butyl hydroperoxide (t-BHP). Incubation of these cells with 2 mM t-BHP causes a rapid depletion of cellular glutathione, followed by a more gradual increase in the contents of malonaldialdehyde and conjugated dienes. Effects of this rapidly evolving oxidative stress were studied on sodium, calcium, and potassium currents of isolated ventricular cells. t-BHP caused a progressive decrease in the magnitude of sodium current obtained on depolarization from a holding potential of -85 mV, which was accompanied by a shift in the reversal potential toward more negative potentials. The voltage dependence of the steady-state parameters for activation and inactivation was shifted, such that in peroxide-exposed cells, there was a greater overlap of activation and inactivation parameters, which would be expected to result in an increased window current. In addition, in the presence of t-BHP, the time constant for activation was decreased at most depolarizing potentials, whereas the time constant for inactivation was increased. The resultant sodium current transients were, therefore, slower in the presence of the peroxide because of slower inactivation. Prolonged exposure of the cells to t-BHP led to a complete and selective inhibition of the Na+ current. However, even when all the Na+ current was inhibited, the K+ and Ca2+ currents remained essentially unaltered. Also, no large outward currents were observed at this stage, indicating that ATP concentration was not drastically decreased. The barrier properties of plasma membrane remained intact, as it was possible to form gigohm seals between the patch pipette and the plasma membrane of cells treated with 2-14 mM t-BHP for up to 30 minutes. These results account for the proarrhythmic effects of free radicals and oxidative stress on cardiac tissues.
Dynamics of atrial peptide secretion in the coronary circulation of the conscious dog.
Authors: Hintze T H , Wang J , Patel M , Schustek M , Ochoa M , Dean R , Chiruzzo F , Zeballos G
Published: June 2012

The secretion of atrial natriuretic peptide by the heart is not simply the arterial-coronary sinus concentration difference times coronary blood flow, because only a small fraction of total coronary blood flow passes through the atria. We measured coronary sinus and arterial plasma atrial natriuretic factor (ANF) concentrations and blood flow to each part of the heart using the radioactive microsphere technique. Before acute volume expansion, the arterial-coronary sinus ANF difference was 305 +/- 23 pg/ml and rose to 1,009 +/- 220 pg/ml during volume expansion, whereas total coronary blood flow rose from 167 to 465 ml/min. Atrial blood flow rose from 2.9% to 4.6% of total coronary blood flow during volume expansion. ANF secretion rate increased from 51 to 469 ng/min. When divided by atrial weight, ANF secretion rate increased from 4.0 +/- 0.3 to 56 +/- 12 ng/min/g atrial tissue-in other words, from 0.3% to 3.7% of tissue ANF content each minute. Dividing by atrial blood flow indicated that the concentration of ANF leaving atrial tissue was 10,000 to 29,651 pg/ml, and the additional secretion of ANF was determined by the increase in coronary blood flow. Therefore, at least two mechanisms are responsible for altering coronary sinus ANF and circulating ANF: the release rate from atrial myocytes and the washout via changes in atrial blood flow.
Acute respiratory acidosis decreases left ventricular contractility but increases cardiac output in dogs.
Authors: Walley K R , Lewis T H , Wood L D
Published: June 2012

To understand the cardiovascular response to respiratory acidosis, we measured hemodynamics, left ventricular pressure, and left ventricular volume (three ultrasonic crystal pairs) during eucapnia and respiratory acidosis in 10 fentanyl-anesthetized open-chest dogs. Left ventricular contractility was assessed primarily by measuring the slope (Emax) and intercept (V0) of the left ventricular end-systolic pressure-volume relation determined by combining end-systolic points from a vena caval occlusion and from brief aortic cross-clamping. Respiratory acidosis (pH 7.09, Pco2 92 mm Hg) reduced contractility by a decrease in Emax (11.4 to 9.2 mm Hg/ml, p less than 0.01) with no change in V0. Despite this, cardiac output increased (1.7 to 2.1 l/min, p less than 0.01), and heart rate increased (96 to 121 beats/min, p less than 0.05), with no change in blood pressure. Systemic vascular resistance fell by 26% (p less than 0.01). During eucapnia, propranolol reduced Emax (11.4 to 4.6 mm Hg/ml, p less than 0.01) with no change in V0. After propranolol treatment, respiratory acidosis further reduced Emax (4.6 to 3.6 mm Hg/ml, p less than 0.05) and increased end-systolic volume more than before propranolol (p less than 0.001). Now cardiac output did not increase even though heart rate increased (81 to 106 beats/min, p less than 0.001) and systemic vascular resistance fell by 20% (p less than 0.01). We conclude that the effect of respiratory acidosis on the circulation is to increase venous return (equals cardiac output) in the face of decreased left ventricular contractility. The beta-adrenergic response to respiratory acidosis substantially ameliorated the increase in end-systolic volume and supported the increase in venous return but did not alter the associated tachycardia or vasodilation. Respiratory acidosis, like propranolol treatment, decreases contractility by decreasing Emax.
Time course of smooth muscle cell proliferation in the intima and media of arteries following experimental angioplasty.
Authors: Hanke H , Strohschneider T , Oberhoff M , Betz E , Karsch K R
Published: June 2012

Smooth muscle cell (SMC) proliferation is known to be an important factor for the development of restenosis after percutaneous transluminal coronary angioplasty. To determine the time course of intimal and medial SMC proliferation and morphological changes after experimental angioplasty, an intimal atheroma was produced with repeated weak electrical stimulations in the right carotid artery of 45 male New Zealand White rabbits. Angioplasty was subsequently performed in 35 rabbits, and the proliferative responses were analyzed with histomorphological and immunohistological criteria at 3, 7, 14, 21, 28, and 42 days after intervention. A hemodynamic relevant stenosis after angioplasty was found in eight (23%) of 35 dilated arteries. In five rabbits the stenosis was due to a mural thrombus, and in three animals restenosis was caused by intimal SMC proliferation. In all dilated arteries the intimal wall thickness increased from 13 +/- 5 intimal cell layers (after electrical stimulation) to 33 +/- 14 cell layers during 28 days after angioplasty (p less than 0.05). Later than 4 weeks after angioplasty, no additional increase of intimal thickening occurred. Application of bromodeoxyuridine 18 and 12 hours before excision of the vessels allowed determination of the percent of cells undergoing DNA synthesis in the intima and media using monoclonal antibody against bromodeoxyuridine. SMCs were identified by alpha-actin staining. Immunohistological quantification of intimal SMC proliferation showed a maximum of cells undergoing DNA synthesis within the first 7 days after angioplasty (p less than 0.01). In contrast, medial proliferation of SMCs was delayed and showed a small but significant increase 21 days after dilatation (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Correlation between transmural high energy phosphate levels and myocardial blood flow in the presence of graded coronary stenosis.
Authors: Path G , Robitaille P M , Merkle H , Tristani M , Zhang J , Garwood M , From A H , Bache R J , Uğurbil K
Published: June 2012

Spatially localized nuclear magnetic resonance spectroscopy was used to investigate with transmural differentiation the response of myocardial high energy phosphate compounds and inorganic orthophosphate (Pi) to graded reductions in coronary blood flow caused by sustained coronary stenosis. In an open-chest model, localized 31P nuclear magnetic resonance spectra from five layers across the left ventricular wall were obtained simultaneously with transmural blood flow measurements during control conditions and during sustained graded reductions in intracoronary pressure. Both the blood flow, and high energy phosphate and Pi contents displayed transmural heterogeneity in response to decreases in intracoronary pressure. The subendocardial creatine phosphate (CP) level remained unchanged as blood flow was reduced to approximately 0.7 ml/min/g wet wt and decreased precipitously beyond this critical flow level. The relation between CP and flow in the midmyocardium and especially in the subepicardium was more complex. Subepicardial CP content did not correlate well with blood flow; however, in cases in which a coronary stenosis resulted in subendocardial hypoperfusion but subepicardial flow was near or above normal, a close correlation was present between subepicardial and subendocardial CP levels. ATP levels in all layers remained unaltered until blood flow was severely reduced. These results demonstrate that 1) the myocardial high energy phosphate and Pi levels at any transmural layer are not generally determined by O2 and blood flow limitation under basal conditions; 2) during subtotal coronary occlusion, increased oxygen extraction is able to meet myocardial needs until a critical level of stenosis is reached; 3) below a critical flow level, subendocardial CP and Pi contents are closely correlated with absolute subendocardial blood flow; and 4) in the presence of a coronary stenosis, subepicardial CP and Pi contents may change even in the absence of perfusion deficit secondary to loss of subendocardial function.