bluuebunny/crossref_metadata_2025 huggingface dataset:
Myogenic and structural properties of cerebral arteries from the stroke-prone spontaneously hypertensive rat
Authors: Izzard Ashley S. , Graham Delyth , Burnham Matthew P. , Heerkens Egidius H. , Dominiczak Anna F. , Heagerty Anthony M.
Published: March 2015

The aims of the study were to compare the myogenic and structural properties of middle cerebral arteries (MCAs) from the stroke-prone spontaneously hypertensive rat (SHRSP) with MCAs from the spontaneously hypertensive rat (SHR) before stroke development in SHRSP. Rats were fed a “Japanese” diet (low-protein rat chow and 1% NaCl in drinking water) for 8 wk, and cerebral arteries were studied in vitro at 12 wk using a pressure arteriograph. Systolic pressure was significantly increased in SHRSP compared with SHR at 12 wk. Between 60 and 180 mmHg, MCAs from SHR maintained an essentially constant diameter, i.e., displayed a “myogenic range,” whereas the diameter of MCAs from SHRSP progressively increased as a function of pressure. Passive lumen diameter of MCAs from SHRSP was reduced at high pressure, and wall thickness and wall/lumen were increased, compared with SHR. Wall cross-sectional area was also increased in MCAs from SHRSP compared with the SHR, indicating growth. The stress-strain relationship was shifted to the left in MCAs from SHRSP, indicating decreased MCA distensibility compared with SHR. However, collagen staining with picrosirius red revealed a redistribution of collagen to the outer half of the MCA wall in SHRSP compared with SHR. These data demonstrate impaired myogenic properties in prestroke SHRSP compared with SHR, which may explain stroke development. The structural differences in MCAs from SHRSP compared with SHR were a consequence of both growth and a reduced distensibility.
Shear modulus of porcine coronary artery: contributions of media and adventitia
Authors: Lu X. , Yang J. , Zhao J. B. , Gregersen H. , Kassab G. S.
Published: March 2015

The epicardial coronary arteries experience significant torsion in the axial direction due to changes in the shape of the heart during the cardiac cycle. The objective of this study was to determine the torsional mechanical properties of the coronary arteries under various circumferential and longitudinal loadings. The coronary artery was treated as a two-layer composite vessel consisting of intima-medial and adventitial layers, and the shear modulus of each layer was determined. Eight porcine hearts were obtained at a local abattoir, and their right coronary and left anterior descending arteries were isolated and tested in vitro with a triaxial torsion machine (inflation, longitudinal stretch, and circumferential twist). After the intact vessel was tested, the adventitia was dissected away, leaving an intact media that was then tested under identical triaxial loading conditions. We proposed a biomechanical analysis to compute the shear modulus of the adventitia from the measured shear moduli of the intact vessel and the media. To validate our predictions, we used four additional hearts in which the shear modulus of the adventitia was measured after dissection of media. Our results show that the shear modulus does not depend on the shear stress or strain but varies linearly with circumferential and longitudinal stresses and in a nonlinear way with the corresponding strains. Furthermore, we found that the shear modulus of the adventitia is larger than that of the intact vessel, which is larger than the vessel media. These results may have important implications for baroreceptor sensitivity, circulation of the vasa vasorum, and coronary dissection.
Spatial heterogeneity of action potential alternans during global ischemia in the rabbit heart
Authors: Qian You-Wen , Sung Ruey J. , Lin Shien-Fong , Province Rose , Clusin William T.
Published: March 2015

Cardiac ischemia causes beat-to-beat fluctuation in action potential duration (APD) alternans, which leads to T wave alternans and arrhythmias. Occurrence of APD alternans that is out of phase at two sites is especially important, but most APD alternans studies have involved rapid pacing of normal myocardium rather than ischemia. To determine the spatial features of APD alternans during ischemia, blood-perfused rabbit hearts were stained with 4-{β-[2(di- n-butylamino)-6-napthyl]vinyl}pyridinium (di-4-ANEPPS) and imaged with a high-resolution camera. Hearts were perfused with oxygenated Tyrode solution at 37°C for staining and then switched to a 50:50% blood/Tyrode mixture. Hearts were paced from the right ventricle at 3/s, and made ischemic by stopping flow for 6 min. Images of 10,000 pixels were obtained at 300 frames/s. Motion artifact was controlled by immobilization and by manual selection of undistorted single-pixel records. Upstroke propagation and conduction isochrones were displayed by computerized image processing. APD alternans was demonstrated in six of seven hearts, and was out of phase in different regions of the image in three hearts. The largest spatial variation in the onset of depolarization to 50% repolarization (APD50) was 155%. This caused beat-to-beat reversal of repolarization. An alternans map could be constructed for well-immobilized portions of the image. There were discrete regions of APD alternans separated by a boundary, as occurs with intracellular Ca2+ concentration alternans. Pixels as close together as 1.1 mm showed an APD alternans that was out of phase. The out-of-phase APD alternans was not due to conduction alternans, as shown by upstroke intervals and conduction isochrones. This contrasts with rapid pacing, where a causal relationship appears to exist. These new observations suggest distinct mechanisms for the genesis of arrhythmias during ischemia.
RV instantaneous intraventricular diastolic pressure and velocity distributions in normal and volume overload awake dog disease models
Authors: Pasipoularides Ares , Shu Ming , Shah Ashish , Tucconi Alessandro , Glower Donald D.
Published: March 2015

Intraventricular diastolic right ventricular (RV) flow field dynamics were studied by functional imaging using three-dimensional (3D) real-time echocardiography with sonomicrometry and computational fluid dynamics in seven awake dogs at control with normal wall motion (NWM) and RV volume overload with diastolic paradoxical septal motion. Burgeoning flow cross section between inflow anulus and chamber walls induces a convective pressure rise, which represents a “convective deceleration load” (CDL). High spatiotemporal resolution dynamic pressure and velocity distributions of the intraventricular RV flow field revealed time-dependent, subtle interactions between intraventricular local acceleration and convective pressure gradients. During the E-wave upstroke, the total pressure gradient along intraventricular flow is the algebraic sum of a pressure decrease contributed by local acceleration and a pressure rise contributed by a convective deceleration that partially counterbalances the local acceleration gradient. This underlies the smallness of early diastolic intraventricular gradients. At peak volumetric inflow, local acceleration vanishes and the total adverse intraventricular gradient is convective. During the E-wave downstroke, the strongly adverse gradient embodies the streamwise pressure augmentations from both local and convective decelerations. It induces flow separation and large-scale vortical motions, stronger in NWM. Their dynamic corollaries on intraventricular pressure and velocity distributions were ascertained. In the NWM pattern, the strong ring-like vortex surrounding the central core encroaches on the area available for flow toward the apex. This results in higher linear velocities later in the downstroke of the E wave than at peak inflow rate. The augmentation of CDL by ventriculoannular disproportion may contribute to E wave and E-to-A ratio depression with chamber dilatation.
Electric currents applied during refractory period enhance contractility and systolic calcium in the ferret heart
Authors: Mohri Satoshi , Shimizu Juichiro , Mika Yuval , Shemer Itzhak , Wang Jie , Ben-Haim Shlomo , Burkhoff Daniel
Published: March 2015

We investigated the mechanism of positive inotropism of electric currents applied during the absolute refractory period. Ten Langendorff-perfused ferret hearts were instrumented to measure isovolumic left ventricular pressure (LVP) and the aequorin luminescence. Biphasic square-wave electric currents (±20 mA, total duration 30 ms) were delivered between pairs of electrodes. Six hearts were perfused at different extracellular Ca2+ concentrations ([Ca2+]o; 1, 2, 4, and 8 mM). These signals increased LVP from 50.0 ± 9.4 to 70.1 ± 14.7, from 67.5 ± 11.0 to 79.0 ± 15.6, from 79.3 ± 21.0 to 87.1 ± 22.8, and from 84.6 ± 24.0 to 91.8 ± 28.5 mmHg at the respective [Ca2+]o ( P< 0.05). Peak free intracellular [Ca2+] ([Ca2+]i) increased from 0.52 ± 0.13 to 1.37 ± 0.23, from 0.76 ± 0.23 to 1.73 ± 0.14, from 1.10 ± 0.24 to 2.05 ± 0.33, and from 1.41 ± 0.36 to 2.24 ± 0.36 μM/ml, respectively ( P < 0.001). With the use of 1 mg/l propranolol with 1 mM [Ca2+]o, LVP and [Ca2+]i were increased significantly from 48.7 ± 8.18 to 56.3 ± 6.11 mmHg and from 0.61 ± 0.11 to 1.17 ± 0.20 μM, respectively ( P < 0.05). In conclusion, positive inotropism of such electrical currents was due to increased peak [Ca2+]i and Ca2+responsiveness of the myofilaments did not change significantly.
Oxidant stress-induced increase in myogenic activation of skeletal muscle resistance arteries in obese Zucker rats
Authors: Frisbee Jefferson C. , Maier Kristopher G. , Stepp David W.
Published: March 2015

This study characterized myogenic activation of skeletal muscle (gracilis) resistance arteries from lean (LZR) and obese Zucker rats (OZR). Arteries from OZR exhibited increased myogenic activation versus LZR; this increase was impaired by endothelium denudation or nitric oxde synthase inhibition. Treatment of vessels with 17-octadecynoic acid impaired responses in both strains by comparable amounts. Dihydroethidine microfluorography indicated elevated vascular superoxide levels in OZR versus LZR; immunohistochemistry demonstrated elevated vascular nitrotyrosine levels in OZR, indicating increased peroxynitrite presence. Vessel treatment with oxidative radical scavengers (polythylene glycol-superoxide dismutase/catalase) or inhibition of Ca2+-activated K+(KCa) channels (iberiotoxin) did not alter myogenic activation in LZR but normalized activation in OZR. Application of peroxynitrite to vessels of OZR caused a greater vasoconstriction versus LZR; the response was impaired in OZR by elevated intraluminal pressure and was abolished in both strains by iberiotoxin. These results suggest that enhanced myogenic activation of gracilis arteries of OZR versus LZR 1) is not due to alterations in cytochrome P-450 contribution, and 2) may be due to elevated peroxynitrite levels inhibiting KCachannels following increased intraluminal pressure.
Deficiency in endothelial nitric oxide synthase impairs myocardial angiogenesis
Authors: Zhao Xue , Lu Xiangru , Feng Qingping
Published: March 2015

We recently demonstrated that mice deficient in endothelial nitric oxide (NO) synthase (eNOS) have congenital septal defects and postnatal heart failure. However, the mechanisms by which eNOS affects heart development are not clear. We hypothesized that deficiency in eNOS impairs myocardial angiogenesis. Myocardial capillary densities were measured morphometrically in neonatal mouse hearts. In vitro tube formation on Matrigel was investigated in cardiac endothelial cells. In vivo myocardial angiogenesis was performed by implanting Matrigel in the left ventricular myocardium. Myocardial capillary densities and VEGF mRNA expression were decreased in neonatal eNOS−/−compared with neonatal wild-type mice ( P < 0.01). Furthermore, in vitro tube formation from cardiac endothelial cells and in vivo myocardial angiogenesis were attenuated in eNOS−/−compared with wild-type mice ( P < 0.01). In vitro tube formation was inhibited by NG-nitro-l-arginine methyl ester in wild-type mice and restored by a NO donor, diethylenetriamine-NO, in eNOS−/−mice ( P < 0.05). In conclusion, deficiency in eNOS decreases VEGF expression and impairs myocardial angiogenesis and capillary development. Decreased myocardial angiogenesis may contribute to cardiac abnormalities during heart development in eNOS−/−mice.
Comparison of buffer and red blood cell perfusion of guinea pig heart oxygenation
Authors: Schenkman Kenneth A. , Beard Daniel A. , Ciesielski Wayne A. , Feigl Eric O.
Published: March 2015

Myocardial mean myoglobin oxygen saturation was determined spectroscopically from isolated guinea pig hearts perfused with red blood cells during increasing hypoxia. These experiments were undertaken to compare intracellular myoglobin oxygen saturation in isolated hearts perfused with a modest concentration of red blood cells (5% hematocrit) with intracellular myoglobin saturation previously reported from traditional buffer-perfused hearts. Studies were performed at 37°C with hearts paced at 240 beats/min and a constant perfusion pressure of 80 cmH2O. It was found that during perfusion with a hematocrit of 5%, baseline mean myoglobin saturation was 93% compared with 72% during buffer perfusion. Mean myoglobin saturation, ventricular function, and oxygen consumption remained fairly constant for arterial perfusate oxygen tensions above 100 mmHg and then decreased precipitously below 100 mmHg. In contrast, mean myoglobin saturation, ventricular function, and oxygen consumption began to decrease even at high oxygen tension with buffer perfusion. The present results demonstrate that perfusion with 5% red blood cells in the perfusate increases the baseline mean myoglobin saturation and better preserves cardiac function at low oxygen tension relative to buffer perfusion. These results suggest that caution should be used in extrapolating intracellular oxygen dynamics from buffer-perfused to blood-perfused hearts.
Inhibition of L-type Ca2+current by C-type natriuretic peptide in bullfrog atrial myocytes: an NPR-C-mediated effect
Authors: Rose R. A. , Lomax A. E. , Giles W. R.
Published: March 2015

Single atrial myocytes were isolated from the bullfrog heart and studied under current and voltage clamp conditions to determine the electrophysiological effects of the C-type natriuretic peptide (CNP). CNP (10–8M) significantly shortened the action potential and reduced its peak amplitude after the application of isoproteronol (10–7M). In voltage clamp studies, CNP inhibited isoproteronol-stimulated L-type Ca2+current ( ICa) without any significant effect on the inward rectifier K+current. The effects of cANF (10–8M), a selective agonist of the natriuretic peptide C receptor (NPR-C), were very similar to those of CNP. Moreover, HS-142-1, an antagonist of the guanylyl cyclase-linked NPR-A and NPR-B receptors did not alter the inhibitory effect of CNP on ICa. Inclusion of cAMP in the recording pipette to stimulate ICaat a point downstream from adenylyl cyclase increased ICa, but this effect was not inhibited by cANF. These results provide the first demonstration that CNP can inhibit ICaafter binding to NPR-C, and suggest that this inhibition involves a decrease in adenylyl cyclase activity, which leads to reduced intracellular levels of cAMP.
Burn plasma mediates cardiac myocyte apoptosis via endotoxin
Authors: Carlson Deborah L. , Lightfoot Ellis , Bryant Debora D. , Haudek Sandra B. , Maass David , Horton Jureta , Giroir Brett P.
Published: March 2015

Thermal trauma is associated with cardiac myocyte apoptosis in vivo. To determine whether cardiac myocyte apoptosis could be secondary to burn-induced cytokines or inflammatory mediators, we investigated the effects of tumor necrosis factor-α (TNF-α) and burn plasma on a murine cardiac myocyte cell line and primary culture myocytes. HL-1 cells were exposed to plasma isolated from burned or sham rats. Burn, but not sham plasma, induced significant increases in caspase-3 activity and DNA fragmentation. Similar results were obtained in primary culture rat myocytes. A dose-dependent increase in caspase-3 activity was observed when HL-1 cells were incubated with increasing concentrations of TNF-α. Even though TNF-α increased apoptosis, enzyme-linked immunosorbent assay detected no TNF-α in burn plasma. Burn plasma also failed to induce TNF-α mRNA, eliminating an autocrine mechanism of TNF-α secretion and binding. Also, treatment of burn plasma containing rhuTNFR:Fc failed to inhibit apoptosis. To examine the possibility that endotoxin within burn plasma might account for the apoptotic effect, burn plasma was preincubated with rBPI21. Caspase-3 activity was reduced to control levels. These data indicate that burn plasma induces apoptosis in cardiac myocytes via an endotoxin-dependent mechanism and suggest that systemic inhibition of endotoxin may provide a therapeutic approach for treatment of burn-associated cardiac dysfunction.
Effects of coupled pacing on cardiac performance during acute atrial tachycardia and fibrillation: an old therapy revisited for a new reason
Authors: Yamada Hirotsugu , Martin David O. , Mowrey Kent A. , Greenberg Neil L. , Wallick Don W.
Published: March 2015

Atrial tachycardia (AT) and fibrillation (AF) result in rapid ventricular rates that are detrimental to optimal cardiac function. The purpose of this study was to determine whether the application of a coupled pacing (CP) regimen would improve ventricular function by decreasing the ventricular rate of mechanical contractions (VRMCs). We simulated AT by pacing either atrium at a rate that resulted in a rapid but regular ventricular rate in seven anesthetized dogs. AF was induced by increasing the atrial pacing rate until atrial activation did not follow the pacing. After the induction of either AT or AF, we applied CP after each intrinsic ventricular activation. We measured the VRMCs and left ventricular (LV) pressures and volumes via a pressure-conductance catheter. The marked reductions in VRMCs during CP resulted in increases in LV end-diastolic volume. The CP resulted in virtually no mechanical contractions, whereas the strength of contractions from the normal electrical activation increased. The increases in the positive LV rate of pressure development over time and LV ejection fraction during CP were the result of postextrasystolic potentiation. The average stroke work (area of the pressure-volume loops) increased as a result of CP during both AT and AF. Despite the large increases in stroke volume (≅2×) during CP, the changes in cardiac output were moderate because the VRMCs markedly decreased (≅½). We conclude that CP therapy may be a viable therapy for slowing the heart rate and improving cardiac performance in patients with AT and AF.
Effects of graded LBNP on MSNA and interstitial norepinephrine
Authors: Khan Mazhar H. , Sinoway Lawrence I. , MacLean David A.
Published: March 2015

Exposure to lower body negative pressure (LBNP) leads to an increased activation of the sympathetic nervous system (SNS) and an increase in muscle sympathetic nerve activity (MSNA). In this study, we examined the relationship between MSNA and interstitial norepinephrine (NEi) concentrations during LBNP. Twelve healthy volunteers were studied (26 ± 6 yr). Simultaneous MSNA and microdialysis data were collected in six of these subjects. Measurements of MSNA (microneurography) and NEi (microdialysis, vastus lateralis) were performed at rest and then during an incremental LBNP paradigm (−10, −30, and −50 mmHg). MSNA rose as a function of LBNP ( P < 0.001, n = 12). The plasma norepinephrine (NEp) concentration was 0.9 ± 0.1 nmol/l at rest ( n = 12). NEi measured in six subjects rose from 5.2 ± 0.8 nmol/l at rest to 17.0 ± 1.7 nmol/l at −50 mmHg ( P < 0.001). Of note, the rise in NEp with LBNP was considerably less compared with the changes in NEi (Δ21 ± 6% vs. Δ197 ± 52%, n = 6, P < 0.015). MSNA and NEi showed a significant linear relationship ( r = 0.721, P < 0.004). Activation of the SNS increased MSNA and NEi levels. The magnitude of the NEi increase was far greater than that seen for NEp suggesting that NE movement into the circulation decreases with baroreceptor unloading.
Physiological concentration of atrial natriuretic peptide induces endothelial regeneration in vitro
Authors: Kook Hyun , Itoh Hiroshi , Choi Bong Seok , Sawada Naoki , Doi Kentaro , Hwang Tae Ju , Kim Kyung Keun , Arai Hiroshi , Baik Yung Hong , Nakao Kazuwa
Published: March 2015

Both nitric oxide (NO) and natriuretic peptides produce apoptosis of vascular smooth muscle cells. However, there is evidence that NO induces endothelial cell proliferation, which suggests that there is a difference in the response of endothelial cells to natriuretic peptides. The purpose of this study was to investigate the effect of atrial natriuretic peptide (ANP) on human endothelial cell survival. ANP within the physiological concentration (10−11mol/l) induced a 52% increase in the number of human coronary arterial endothelial cells and a 63% increase in human umbilical vein endothelial cells at a low concentration of serum. The increase in cell numbers was blocked by pretreatment with RP8-CPT-cGMP (RP8), a cGMP-dependent protein kinase inhibitor, with wortmannin, an Akt/PKB inhibitor, and with PD-98059, an ERK1/2 inhibitor. In a Transwell migration test, ANP also increased the cell migration, and RP8, wortmannin, and PD-98059 blocked this increase. A wound healing assay was performed to examine the effects of ANP on regeneration in vitro. ANP increased both cell numbers and migration, but the effects were blocked by the above three kinase inhibitors. ANP increased the expression of phospho-Akt and of phospho-ERK1/2 within 1.5 h. These results suggest that ANP can potentiate endothelial regeneration by cGMP-dependent protein kinase stimulation and subsequent Akt and ERK1/2 activations.
IRAK contributes to burn-triggered myocardial contractile dysfunction
Authors: Thomas James A. , Tsen May F. , White D. Jean , Horton Jureta W.
Published: March 2015

Major burn injury causes myocardial contractile dysfunction, but the molecular basis of this physiological response is incompletely understood. Previous studies demonstrated a role for the interleukin-1 receptor-associated kinase (IRAK) in the cardiac response to acute lipopolysaccharide administration as well as congestive heart failure. In this study, we examined the contribution of IRAK to burn-mediated cardiac responses. After burn injury, hearts from wild-type and IRAK-deficient mice were compared for intracellular signaling pathway activation and contractile function. IRAK-deficient hearts showed impaired activation of kinases that function downstream of IRAK and were partially protected against burn-induced contractile dysfunction. The findings demonstrate that IRAK and the Toll/interleukin-1 pathways participate in the response to large body surface area burns that leads to impaired cardiac contractility.
Tonin in rat heart with experimental hypertrophy
Authors: Borges Júlio César , Silva JoséAntônio , Gomes Maria Aparecida , Lomez Eliane Sa Lopes , Leite Katia Moraes , Araujo Ronaldo Carvalho , Bader Michael , Pesquero João Bosco , Pesquero Jorge Luiz
Published: March 2015

The present study was undertaken to determine tonin expression and activity in rat heart presenting isoproterenol-induced hypertrophy. Renin, angiotensin-converting enzyme (ACE), and angiotensinogen (AG) expression were also determined. Wistar rats were treated with isoproterenol for 7 days (5 mg · kg−1· day−1sc). For untreated animals, the levels of tonin-specific activity in the atrium were 2.6- and 5.5-fold higher than those of the left and right ventricle, respectively. After treatment, the levels of tonin-specific activity increased twofold in the atrium but did not change in the ventricles. Renin expression was not detectable in these structures, and ACE expression levels did not change with treatment. AG expression was detected in the left ventricle at very low levels compared with the atrium and increased significantly only in the hypertrophied atrium (1.8-fold). Tonin mRNA was not detected in the ventricle but was found at low levels in the atrium, which increased after isoproterenol treatment. Our results permit us to conclude that tonin may play a role in the process of heart hypertrophy in the rat.
Temperature-dependent postextrasystolic potentiation and Ca2+ recirculation fraction in canine hearts
Authors: Mizuno Ju , Araki Junichi , Suzuki Shunsuke , Mohri Satoshi , Mikane Takeshi , Shimizu Juichiro , Matsubara Hiromi , Hirakawa Masahisa , Ohe Tohru , Suga Hiroyuki
Published: March 2015

We have found that cardiac temperature proportionally changes O2 cost of contractility, defined as O2 consumption for myocardial total Ca2+handling normalized to contractility in terms of the end-systolic pressure-volume ratio (maximal elastance, E max), in the canine left ventricle (temperature sensitivity, Q10 = 2). We have separately found that a decrease in the recirculation fraction (RF) of Ca2+ within myocardial cells underlies an increased O2 cost of E max in stunned hearts. We therefore hypothesized that a similar change in RF would underlie the Q10 of O2 cost of E max. We tested this hypothesis by analyzing RF calculated from an exponential decay component of the transiently alternating postextrasystolic potentiation in the canine left ventricle. RF decreased from 0.7 to 0.5 as cardiac temperature increased from 33 to 38°C with Q10 of 0.5, reciprocal to that of O2 cost of E max. We conclude that Q10 of ATP-consuming reactions involved in Ca2+handling and E max response to it could reasonably account for the reciprocal Q10 of RF and O2 cost of E max.
Diminished arteriolar responses in nitrate tolerance involve ROS and angiotensin II
Authors: Frame Mary D. , Fox Randall J. , Kim Dongsoo , Mohan Amy , Berk Bradford C. , Yan Chen
Published: March 2015

Our purpose was to evaluate hyporesponsivity to nitric oxide (NO)-induced dilation in small arterioles during nitrate tolerance. An Alza osmotic pump was implanted in the left flank of adult rats ( n = 56) for continuous administration of nitroglycerin (140 μg/h) or vehicle (propylene glycol). On postoperative day 3, arcade (∼50-μm diameter) and terminal (∼20 μm) arterioles were observed in the cremaster preparation with in vivo video microscopy. Local vascular responses were obtained with micropipette-applied NO donors, with and without superoxide dismutase (SOD), Mn(III) tetrakis(4-benzoic acid) porphyrin chloride (MnTBAP), or losartan. On day 3, NO-mediated dilation was significantly attenuated in nitroglycerin-treated rats. Attenuation was greater in the terminal arterioles compared with the arcades. Control responses were restored by SOD, MnTBAP, or losartan, suggesting a role for elevated angiotensin II and reactive oxygen species (ROS) as mediators of the attenuated NO dilation (nitrate tolerance). Addition of losartan to the drinking water likewise prevented nitrate tolerance. In summary, terminal arterioles are affected by nitrates to a greater extent than the arcade arterioles that feed them, in a process dependent on angiotensin II and ROS.
Protection afforded by ischemic preconditioning is not mediated by effects on cell-to-cell electrical coupling during myocardial ischemia-reperfusion
Authors: Padilla Ferran , Garcia-Dorado David , Rodríguez-Sinovas Antonio , Ruiz-Meana Marisol , Inserte Javier , Soler-Soler Jordi
Published: March 2015

The end-effectors of ischemic preconditioning (IPC) are not well known. It has been recently shown that transgenic mice underexpressing the gap junction protein connexin43 (Cx43) cannot be preconditioned. Because gap junctions allow spreading of cell death during ischemia-reperfusion in different tissues, including myocardium, we hypothesized that the protection afforded by IPC is mediated by effects on gap junction-mediated intercellular communication. To test this hypothesis, we analyzed the effect of IPC (5 min ischemia-5 min reperfusion × 2) on the changes in electrical impedance (four electrode probe) and impulse propagation velocity (transmembrane action potential) induced by ischemia (60 min) and reperfusion (60 min) in isolated rat hearts. IPC ( n = 8) reduced reperfusion-induced lactate dehydrogenase release by 65.8% with respect to control hearts ( n = 9) ( P = 0.04) but had no effect on the time of onset of rigor contracture (increase in diastolic tension), electrical uncoupling (sharp changes in tissue resistivity and phase angle in impedance recordings), or block of impulse propagation during ischemia. Normalization of electrical impedance during reperfusion was also unaffected by IPC. The lack of effect of IPC on ischemic rigor contracture and on changes in tissue impedance during ischemia-reperfusion were validated under in vivo conditions in pigs submitted to 48 min of coronary occlusion and 120 min of reperfusion. IPC ( n = 12) reduced infarct size (triphenyltetrazolium) by 64.9% ( P = 0.01) with respect to controls ( n = 17). We conclude that the protection afforded by IPC is not mediated by effects on electrical coupling. This result is consistent with recent findings suggesting that Cx43 could have effects on cell survival independent on changes in cell-to-cell communication.
Impact of pericardial restraint on right atrial mechanics during acute right ventricular pressure load
Authors: Maniar Hersh S. , Prasad Sunil M. , Gaynor Sydney L. , Chu Celeste M. , Steendijk Paul , Moon Marc R.
Published: March 2015

Optimization of right atrial (RA) mechanics is important for maintaining right ventricular (RV) filling and global cardiac output. However, the impact of pericardial restraint on RA function and the compensatory role of the right atrium to changes in RV afterload remain poorly characterized. In eight open-chest sheep, RA elastance (contractility) and chamber stiffness were measured (RA pressure-volume relations) at baseline and during partial pulmonary artery (PA) occlusion. Data were collected before and after pericardiotomy. With the pericardium intact and partial PA occlusion, RA elastance increased by 28% ( P < 0.04), whereas RA stiffness tended to rise ( P = 0.08). However, after pericardiotomy, there was a significant fall in both RA elastance (54%, P < 0.04) and stiffness (39%, P < 0.04), and subsequent PA occlusion failed to induce a change in elastance ( P > 0.19) or stiffness ( P > 0.84). After pericardiotomy, RA elastance and stiffness fell dramatically, and the compensatory response of the right atrium to elevated RV afterload was lost. The ability of the right atrium to respond to changes in RV hemodynamics is highly dependent on pericardial integrity.
Preconditioning prevents alterations in cardiac SR gene expression due to ischemia-reperfusion
Authors: Temsah Rana M. , Kawabata Kenichi , Chapman Donald , Dhalla Naranjan S.
Published: March 2015

We have previously shown that ischemic preconditioning (IP) improves cardiac performance and sarcoplasmic reticulum (SR) function in hearts subjected to ischemia-reperfusion (I/R). In this study, we examined the effect of IP on I/R-induced changes in gene expression for SR proteins such as the Ca2+ release channel, Ca2+ pump ATPase, phospholamban, and calsequestrin in the isolated rat heart. Normal isolated rat hearts exposed to three brief cycles of IP (5-min ischemia and 5-min reperfusion) exhibited a significant decrease in the transcript levels of SR genes. Nonpreconditioned I/R hearts when subjected to 30-min ischemia and 30-min reperfusion showed a marked decrease in mRNA levels for the SR proteins compared with normal hearts; this decrease was attenuated by preconditioning. Although hearts subjected to Ca2+ paradox (CP) have been shown to exhibit intracellular Ca2+ overload and SR dysfunction like those in I/R hearts, virtually nothing is known regarding the effect of CP on cardiac SR gene expression. Accordingly, CP (5-min Ca2+-free perfusion and 30-min reperfusion with normal medium) was observed to produce dramatic changes in SR gene expression, and the heart failed to contract; these alterations were attenuated by IP. Our results show that 1) both I/R and CP depress SR gene expression in the normal heart, 2) IP attenuates I/R- and CP-induced depression in cardiac function and SR gene expression, and 3) intracellular Ca2+ overload may play a role in depressing SR gene expression in both I/R and CP hearts.
Estimation of preload recruitable stroke work relationship by a single-beat technique in humans
Authors: Lee Wen-Shin , Huang Wen-Pin , Yu Wen-Chung , Chiou Kuan-Rau , Ding Philip Yu-An , Chen Chen-Huan
Published: March 2015

The slope of the preload recruitable stroke work relationship (Mw) is a highly linear, load-insensitive contractile index. To investigate whether Mwcan be determined from a single steady-state beat, 45 patients were studied during cardiac catheterization. Single-beat Mw(SBMw) was calculated directly from the baseline stroke work and baseline left ventricular (LV) end-diastolic volume (EDVB), and the volume-axis intercept (Vw) was estimated as k × EDVB+ ( k − 1) × LVwall, where k is the ratio of the epicardial shell volumes corresponding to Vwand EDVBand LVwallis the wall volume. The mean of individual k values was 0.72 ± 0.04, which correlated with LV mass significantly ( r = 0.60, P < 0.001). SBMwcalculated from a constant k of 0.7 predicted Mwwell ( r = 0.88, P < 0.0001), and the prediction improved slightly when k was estimated from individual LV mass ( r = 0.93, P < 0.0001). Subgroup analyses revealed that the single-beat technique also worked in patients with small or large LV mass or volume or with regional wall motion abnormalities. The absolute change in SBMwafter dobutamine infusion also correlated with that in Mw. In conclusion, Mwcan be estimated from a steady-state beat without alteration of preload.
Validation of OPS imaging for microvascular measurements during isovolumic hemodilution and low hematocrits
Authors: Harris A. G. , Sinitsina I. , Messmer K.
Published: March 2015

Orthogonal polarization spectral (OPS) imaging is a new technique that can be used to visualize the microcirculation with reflected light. It uses hemoglobin absorption to visualize the red blood cells (RBCs). Thus the method could fail at low hematocrit (Hct). The aim of this study was to validate OPS imaging for quantitative measurements of diameter and functional capillary density (FCD) under conditions of hemodilution of varying degrees to achieve a wide range of Hcts. The validation was performed in the dorsal skinfold chamber of nine awake Syrian golden hamsters. Measurements of vessel diameter and FCD were performed off-line using Cap-Image on video sequences captured using OPS imaging and standard intravital fluorescence microscopy at baseline, 85, 70, 55, and 40% of the initial Hct. For hemodilution, isovolumic exchange of blood for 6% Dextran 60 was performed. Bland-Altman plots for the vessel diameter and FCD show good agreement between the two methods for both parameters at all studied Hcts. As expected, there was a systematic bias of ∼4 μm in the diameter measurements since the RBC column was measured and not the intravascular diameter. In conclusion, OPS imaging can be used to measure diameter and FCD at a wide range of Hcts.
Hyperhomocysteinemia leads to adverse cardiac remodeling in hypertensive rats
Authors: Joseph Jacob , Washington Abeer , Joseph Lija , Koehler Laura , Fink Louis M. , Hauer-Jensen Martin , Kennedy Richard H.
Published: March 2015

Hyperhomocysteinemia (Hhe), linked to cardiovascular disease by epidemiological studies, may be an important factor in adverse cardiac remodeling in hypertension. Specifically, convergence of myocardial and vascular alterations promoted by Hhe and hypertension may exacerbate cardiac remodeling and myocardial dysfunction. We studied male spontaneously hypertensive rats fed one of three diets: control, intermediate Hhe inducing, or severe Hhe inducing. After 10 wk of dietary intervention, cardiac function was assessed in vitro, and cardiac and coronary arteriolar remodeling were monitored by histomorphometric, immunohistochemical, and biochemical techniques. Results showed that Hhe induced diastolic dysfunction, as characterized by the diastolic pressure-volume curve, without significant changes in baseline systolic function. Perivascular collagen levels were increased by Hhe, and there was an increase in left ventricular hydroxyproline levels. Myocyte size was not affected. Coronary arteriolar wall thickness increased with Hhe due to smooth muscle hyperplasia. Mast cells increased in parallel with Hhe and collagen accumulation. In summary, 10 wk of Hhe caused coronary arteriolar remodeling, myocardial collagen deposition, and diastolic dysfunction in hypertensive rats.
Botulinum neurotoxin A attenuates release of norepinephrine but not NPY from vasoconstrictor neurons
Authors: Morris Judy L. , Jobling Phillip , Gibbins Ian L.
Published: March 2015

We examined effects of botulinum neurotoxin A (BoNTA) on sympathetic constrictions of the vena cava and uterine artery from guinea pigs to test the role of soluble NSF attachment protein receptor (SNARE) proteins in release of the cotransmitters norepinephrine (NE) and neuropeptide Y (NPY). Protein extracts of venae cavae and uterine arteries showed partial cleavage of synaptosomal associated protein of 25 kDa (SNAP-25) after treatment in vitro with BoNTA (50–100 nM). The rising phase of isometric contractions of isolated venae cavae to field stimulation at 20 Hz, mediated by NE acting on α-adrenoceptors, was reduced significantly by 100 nM BoNTA. However, sustained sympathetic contractions mediated by NPY were not affected by BoNTA. In uterine arteries, noradrenergic contractions to 1-Hz stimulation were almost abolished by BoNTA, and contractions at 10 Hz were reduced by 50–60%. We conclude that SNARE proteins are involved in exocytosis of NE from synaptic vesicles at low frequencies of stimulation but may not be essential for exocytosis of NPY and NE from large vesicles at high stimulation frequencies.
Apoptosis in the left ventricle of chronic volume overload causes endocardial endothelial dysfunction in rats
Authors: Cox Michael J. , Sood Harpreet S. , Hunt Matthew J. , Chandler Derrick , Henegar Jeffrey R. , Aru Giorgio M. , Tyagi Suresh C.
Published: March 2015

The hypothesis is that chronic increases in left ventricular (LV) load induce oxidative stress and latent matrix metalloproteinase (MMP) is activated, allowing the heart to dilate in the absence of endothelial nitric oxide (NO) and thereby reduce filling pressure. To create volume overload, an arteriovenous (A-V) fistula was placed in male Sprague-Dawley rats. To decrease oxidative stress and apoptosis, 0.08 mg/ml nicotinamide (Nic) was administered in drinking water 2 days before surgery. The rats were divided into the following groups: 1) A-V fistula, 2) A-V fistula + Nic, 3) sham operated, 4) sham + Nic, and 5) control (unoperated); n = 6 rats/group. After 4 wk, hemodynamic parameters were measured in anesthetized rats. The heart was removed and weighed, and LV tissue homogeneates were prepared. A-V fistula caused an increase in heart weight, lung weight, and end-diastolic pressure compared with the sham group. The levels of malondialdehyde (MDA; a marker of oxidative stress) was 6.60 ± 0.23 ng/mg protein and NO was 6.87 ± 1.21 nmol/l in the LV of A-V fistula rats by spectrophometry. Nic treatment increased NO to 13.88 ± 2.5 nmol/l and decreased MDA to 3.54 ± 0.34 ng/mg protein ( P= 0.005). Zymographic levels of MMP-2 were increased, as were protein levels of nitrotyrosine and collagen fragments by Western blot analysis. The inhibition of oxidative stress by Nic decreased nitrotyrosine content and MMP activity. The levels of tissue inhibitor of metalloproteinase-4 mRNA were decreased in A-V fistula rats and increased in A-V fistula rats treated with Nic by Northern blot analysis. TdT-mediated dUTP nick-end labeling-positive cells were increased in A-V fistula rats and decreased in fistula rats treated with Nic. Acetylcholine and nitroprusside responses in cardiac rings prepared from the above groups of rats suggest impaired endothelial-dependent cardiac relaxation. Treatment with Nic improves cardiac relaxation. The results suggest that an increase in the oxidative stress and generation of nitrotyrosine are, in part, responsible for the activation of metalloproteinase and decreased endocardial endothelial function in chronic LV volume overload.
Hydrogen peroxide induces endothelium-dependent and -independent coronary arteriolar dilation: role of cyclooxygenase and potassium channels
Authors: Thengchaisri Naris , Kuo Lih
Published: March 2015

Hydrogen peroxide, a relatively stable reactive oxygen species, is known to elicit vasodilation, but its underlying mechanism remains elusive. Here, we examined the role of endothelial nitric oxide (NO), prostaglandin, cytochrome P-450-derived metabolites, and smooth muscle potassium channels in coronary arteriolar dilation to abluminal H2O2. Pig subepicardial coronary arterioles (50–100 μm) were isolated and pressurized without flow for in vitro study. Arterioles developed basal tone and dilated dose dependently to H2O2(1–100 μM). Disruption of th endothelium and inhibition of cyclooxygenase (COX) by indomethacin produced identical attenuation of vasodilation to H2O2. Conversely, the vasodilation to H2O2was not affected by either the NO synthase inhibitor NG-nitro-l-arginine methyl ester or the cytochrome P-450 enzyme blocker miconazole. Inhibition of the COX-1, but not the COX-2 pathway, attenuated H2O2-induced dilation similarly to indomethacin. The production of prostaglandin E2(PGE2), but not prostaglandin I2, from coronary arterioles was significantly increased by H2O2. Furthermore, inhibition of PGE2receptors with AH-6809 attenuated vasodilation to H2O2similar to that produced by indomethacin. In the absence of a functional endothelium, H2O2-induced dilation was attenuated, in an identical manner, by a depolarizing agent KCl and a calcium-activated potassium (KCa) channel inhibitor iberiotoxin. However, PGE2-induced dilation was not affected by iberiotoxin. The endothelium-independent dilation to H2O2was also insensitive to the inhibition of guanylyl cyclase, lipoxygenase, ATP-sensitive potassium channels, and inward rectifier potassium channels. These results suggest that H2O2induces endothelium-dependent vasodilation through COX-1-mediated release of PGE2and also directly relaxes smooth muscle by hyperpolarization through KCachannel activation.
Balance between myogenic, flow-dependent, and metabolic flow control in coronary arterial tree: a model study
Authors: Cornelissen Annemiek J. M. , Dankelman Jenny , VanBavel Ed , Spaan Jos A. E.
Published: March 2015

Myogenic response, flow-dependent dilation, and direct metabolic control are important mechanisms controlling coronary flow. A model was developed to study how these control mechanisms interact at different locations in the arteriolar tree and to evaluate their contribution to autoregulatory and metabolic flow control. The model consists of 10 resistance compartments in series, each representing parallel vessel units, with their diameters determined by tone depending on either flow and pressure [flow-dependent tone reduction factor (TRFflow) × Tonemyo] or directly on metabolic factors (Tonemeta). The pressure-Tonemyo and flow-TRFflow relations depend on the vessel size obtained from interpolation of data on isolated vessels. Flow-dependent dilation diminishes autoregulatory properties compared with pressure-flow lines obtained from vessels solely influenced by Tonemyo. By applying Tonemeta to the four distal compartments, the autoregulatory properties are restored and tone is equally distributed over the compartments. Also, metabolic control and blockage of nitric oxide are simulated. We conclude that a balance is required between the flow-dependent properties upstream and the constrictive metabolic properties downstream. Myogenic response contributes significantly to flow regulation.
Bicarbonate-dependent superoxide release and pulmonary artery tone
Authors: Nozik-Grayck Eva , Huang Yuh-Chin T. , Carraway Martha Sue , Piantadosi Claude A.
Published: March 2015

Pulmonary vasoconstriction is influenced by inactivation of nitric oxide (NO) with extracellular superoxide ([Formula: see text]). Because the short-lived [Formula: see text] anion cannot diffuse across plasma membranes, its release from vascular cells requires specialized mechanisms that have not been well delineated in the pulmonary circulation. We have shown that the bicarbonate [Formula: see text] anion exchange protein (AE2) expressed in the lung also exchanges [Formula: see text] for [Formula: see text]. Thus we determined whether [Formula: see text] release involved in pulmonary vascular tone depends on extracellular [Formula: see text]. We assessed endothelium-dependent vascular reactivity and [Formula: see text] release in the presence or absence of [Formula: see text] in pulmonary artery (PA) rings isolated from normal rats and those exposed to hypoxia for 3 days. Lack of extracellular [Formula: see text] in normal PA rings significantly attenuated endothelial [Formula: see text] release, opposed hypoxic vasoconstriction, and enhanced acetylcholine-mediated vasodilation. Release of [Formula: see text] was also inhibited by an AE2 inhibitor (SITS) and abolished in normoxia by an NO synthase inhibitor ( NG-nitro-l-arginine methyl ester). In contrast, hypoxia increased PA AE2 protein expression and [Formula: see text] release; the latter was not affected by NG-nitro-l-arginine methyl ester or other inhibitors of enzymatic [Formula: see text] generation. Enhanced [Formula: see text] release by uncoupling NO synthase with geldanamycin was attenuated by hypoxia or by [Formula: see text] elimination. These results indicate that [Formula: see text] produced by endothelial NOS in normoxia and unidentified sources in hypoxia regulate pulmonary vascular tone via AE2.
Reactive oxygen species induce reversible PECAM-1 tyrosine phosphorylation and SHP-2 binding
Authors: Maas Matthias , Wang Ronggang , Paddock Cathy , Kotamraju Srigiridhar , Kalyanaraman Balaraman , Newman Peter J. , Newman Debra K.
Published: March 2015

Platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) functions to control the activation and survival of the cells on which it is expressed. Many of the regulatory functions of PECAM-1 are dependent on its tyrosine phosphorylation and subsequent recruitment of the Src homology (SH2) domain containing protein tyrosine phosphatase SHP-2. The recent demonstration that PECAM-1 tyrosine phosphorylation occurs in cells exposed to the reactive oxygen species hydrogen peroxide (H2O2) suggested that this form of oxidative stress may also support PECAM-1/SHP-2 complex formation. In the present study, we show that PECAM-1 tyrosine phosphorylation in response to exposure of cells to H2O2 is reversible, involves a shift in the balance between kinase and phosphatase activities, and supports binding of SHP-2 and recruitment of this phosphatase to cell-cell borders. We speculate, however, that the unique ability of H2O2 to reversibly oxidize the reactive site cysteine residues of protein tyrosine phosphatases may result in transient inactivation of the SHP-2 that is bound to PECAM-1 under these conditions. Finally, we provide evidence that PECAM-1 tyrosine phosphorylation and SHP-2 binding in endothelial cells requires exposure to an “oxidative burst” of H2O2, but that exposure of these cells to sufficiently high concentrations of H2O2 for a sufficiently long period of time abrogates binding of SHP-2 to tyrosine-phosphorylated PECAM-1. These findings support a role for PECAM-1 as a sensor of oxidative stress, perhaps most importantly during the process of inflammation.