bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistence of gap junction communication during myocardial ischemia
Authors: Ruiz-Meana Marisol , Garcia-Dorado David , Lane Sinead , Pina Pilar , Inserte Javier , Mirabet Maribel , Soler-Soler Jordi
Published: December 2017

During myocardial ischemia, severe ATP depletion induces rigor contracture followed by intracellular Ca2+ concentration ([Ca2+]i) rise and progressive impairment of gap junction (GJ)-mediated electrical coupling. Our objective was to investigate whether chemical coupling through GJ allows propagation of rigor in cardiomyocytes and whether it persists after rigor development. In end-to-end connected adult rat cardiomyocytes submitted to simulated ischemia the interval between rigor onset was 3.7 ± 0.7 s, and subsequent [Ca2+]i rise was virtually identical in both cells, whereas in nonconnected cell pairs the interval was 71 ± 12 s and the rate of [Ca2+]i rise was highly variable. The GJ blocker 18α-glycyrrhetinic acid increased the interval between rigor onset and the differences in [Ca2+]i between connected cells. Transfer of Lucifer yellow demonstrated GJ permeability 10 min after rigor onset in connected cell pairs, and 30 min after rigor onset in isolated rat hearts submitted to nonflow ischemia but was abolished after 2 h of ischemia. GJ-mediated communication allows propagation of rigor in ischemic myocytes and persists after rigor development despite acidosis and increased [Ca2+]i.
Oxygen delivery at high blood viscosity and decreased arterial oxygen content to brains of conscious rats
Authors: Rebel A. , Lenz C. , Krieter H. , Waschke K. F. , Van Ackern K. , Kuschinsky W.
Published: December 2017

We addressed the question to which extent cerebral blood flow (CBF) is maintained when, in addition to a high blood viscosity (Bvis) arterial oxygen content (CaO2 ) is gradually decreased. CaO2 was decreased by hemodilution to hematocrits (Hct) of 30, 22, 19, and 15% in two groups. One group received blood replacement (BR) only and served as the control. The second group received an additional high viscosity solution of polyvinylpyrrolidone (BR/PVP). Bvis was reduced in the BR group and was doubled in the BR/PVP. Despite different Bvis, CBF did not differ between BR and BR/PVP rats at Hct values of 30 and 22%, indicating a complete vascular compensation of the increased Bvis at decreased CaO2 . At an Hct of 19%, local cerebral blood flow (LCBF) in some brain structures was lower in BR/PVP rats than in BR rats. At the lowest Hct of 15%, LCBF of 15 brain structures and mean CBF were reduced in BR/PVP. The resulting decrease in cerebral oxygen delivery in the BR/PVP group indicates a global loss of vascular compensation. We concluded that vasodilating mechanisms compensated for Bvis increases thereby maintaining constant cerebral oxygen delivery. Compensatory mechanisms were exhausted at a Hct of 19% and lower as indicated by the reduction of CBF and cerebral oxygen delivery.
Maintained contractile reserve in a transgenic mouse model of myocardial stunning
Authors: Kögler Harald , Soergel David G. , Murphy Anne M. , Marbán Eduardo
Published: December 2017

Cardiac excitation-contraction (E-C) coupling is impaired at the myofilament level in the reversible postischemic dysfunction known as “stunned” myocardium. We characterized tension development and calcium cycling in intact isolated trabeculae from transgenic (TG) mice expressing the major proteolytic degradation fragment of troponin I (TnI) found in stunned myocardium (TnI1–193) and determined the ATPase activity of myofibrils extracted from TG and non-TG mouse hearts. The phenotype of these mice at baseline recapitulates that of stunning. Here, we address the question of whether contractile reserve is preserved in these mice, as it is in genuine stunned myocardium. During twitch contractions, calcium cycling was normal, whereas tension was greatly reduced, compared with non-TG controls. A decrease in maximum Ca2+-activated tension and Ca2+desensitization of the myofilaments accounted for this contractile dysfunction. The decrease in maximum tension was paralleled by an equivalent decrease in maximum Ca2+-activated myofibrillar ATPase activity. Exposure to high calcium or isoproterenol recruited a sizable contractile reserve in TG muscles, which was proportionately similar to that in control muscles but scaled downward in amplitude. These results suggest that calcium regulatory pathways and β-adrenergic signal transduction remain intact in isolated trabeculae from stunned TG mice, further recapitulating key features of genuine stunned myocardium.
Transmural reentry during acute global ischemia and reperfusion in canine ventricular muscle
Authors: Wu Jiashin , Zipes Douglas P.
Published: December 2017

Coronary occlusion and reperfusion produce tachyarrhythmias. We tested the hypothesis that variations in transmural activation after global ischemia and reperfusion were responsible for arrhythmias. We arterially perfused 36 isolated transmural wedges from canine left ventricular free walls. After ≥100 min of stabilization, the artery was occluded for 25 min, followed by reperfusion at various flow rates. We recorded 256 channels of fluorescent action potentials on transmural surfaces from preocclusion to >15 min after reperfusion. During endocardial pacing at 300 ms, ischemia of ≥570 ± 165 s ( n = 34) produced 1:1 endocardial conduction and then 2:1 and 4:1 block as the wave fronts conducted toward epicardium. Transmural reentry appeared after 535 ± 146 s of ischemia ( n = 31). Further ischemia caused epicardial inactivation and eliminated reentry ( n = 24). During reperfusion, tissues progressed through sequences of epicardial inactivation and reappearance of activation with 1:1, 2:1, and 4:1 conduction; both sustained and nonsustained reentry occurred. We conclude that heterogeneous activation responses to endocardial pacing during acute ischemia provide the substrate for initiating reentry, suppressed reentry during further ischemia, and caused reentry during reperfusion.
Homocysteine induces monocyte chemoattractant protein-1 expression by activating NF-κB in THP-1 macrophages
Authors: Wang Guoping , Siow Yaw L. , O Karmin
Published: December 2017

Homocysteinemia is an independent risk factor for cardiovascular disorders. The recruitment of monocytes is an important event in atherogenesis. Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that stimulates monocyte migration into the intima of arterial walls. The objective of the present study was to investigate the effect of homocysteine on MCP-1 expression in macrophages and the underlying mechanism of such effect. Human monocytic cell (THP-1)-derived macrophages were incubated with homocysteine. By nuclease protection assay and ELISA, homocysteine (0.05–0.2 mM) was shown to significantly enhance the expression of MCP-1 mRNA (up to 2.6-fold) and protein (up to 4.8-fold) in these cells. Homocysteine-induced MCP-1 expression resulted in increased monocyte chemotaxis. The increase in MCP-1 expression was associated with activation of nuclear factor (NF)-κB due to increased phosphorylation of the inhibitory protein (IκB-α) as well as reduced expression of IκB-α mRNA in homocysteine-treated cells. In conclusion, our results demonstrate that homocysteine, at pathological concentration, stimulates MCP-1 expression in THP-1 macrophages via NF-κB activation.
Time course of structural adaptations in chronic AV block dogs: evidence for differential ventricular remodeling
Authors: Verduyn S. Cora , Ramakers Christian , Snoep Gabriel , Leunissen Jet D. M. , Wellens Hein J. J. , Vos Marc A.
Published: December 2017

To determine the nature and time course of biventricular hypertrophy and concomitant electrical and mechanical changes after creation of complete atrioventricular block (CAVB), six adult dogs (22–30 kg) were subjected to serial magnetic resonance imaging (MRI) and electrocardiography. After 6 days of CAVB, left ventricular (LV) mass, ejection fraction (EF), and Q-T time at a paced rhythm of 60 beats/min were already significantly increased. Maximal values were reached within 14–21 days of CAVB: LV mass, from 116 ± 11 to 143 ± 12 g; right ventricular (RV) mass, from 40 ± 3 to 55 ± 6 g; EF, from 68 ± 6% to 86 ± 5%; and Q-T time, from 285 ± 25 to 330 ± 35 ms, all P < 0.05. Cardiac output returned to baseline at day 14. End-diastolic wall thickness increased only in the RV, in which angiotensin type 1 (AT1) receptor mRNA expression was significantly greater. The autopsy correlated well with the MRI results ( r = 0.98, P≤ 0.01). In conclusion, electrophysiological, mechanical, and structural adaptation processes after bradycardia-induced volume overload develop rapidly and are completed within 3 wk. The degree of hypertrophy was greater in the RV, which was associated with an increase in AT1receptor mRNA.
Nonlinear dynamics of heart rate variability in cocaine-exposed neonates during sleep
Authors: Garde Smita , Regalado Michael G. , Schechtman Vicki L. , Khoo Michael C. K.
Published: December 2017

The aim of this study was to determine the effects of prenatal cocaine exposure (PCE) on the dynamics of heart rate variability in full-term neonates during sleep. R-R interval (RRI) time series from 9 infants with PCE and 12 controls during periods of stable quiet sleep and active sleep were analyzed using autoregressive modeling and nonlinear dynamics. There were no differences between the two groups in spectral power distribution, approximate entropy, correlation dimension, and nonlinear predictability. However, application of surrogate data analysis to these measures revealed a significant degree of nonlinear RRI dynamics in all subjects. A parametric model, consisting of a nonlinear delayed-feedback system with stochastic noise as the perturbing input, was employed to estimate the relative contributions of linear and nonlinear deterministic dynamics in the data. Both infant groups showed similar proportional contributions in linear, nonlinear, and stochastic dynamics. However, approximate entropy, correlation dimension, and nonlinear prediction error were all decreased in active versus quiet sleep; in addition, the parametric model revealed a doubling of the linear component and a halving of the nonlinear contribution to overall heart rate variability. Spectral analysis indicated a shift in relative power toward lower frequencies. We conclude that 1) RRI dynamics in infants with PCE and normal controls are similar; and 2) in both groups, sympathetic dominance during active sleep produces primarily periodic low-frequency oscillations in RRI, whereas in quiet sleep vagal modulation leads to RRI fluctuations that are broadband and dynamically more complex.
Shear stress regulates occludin content and phosphorylation
Authors: DeMaio Lucas , Chang Yong S. , Gardner Thomas W. , Tarbell John M. , Antonetti David A.
Published: December 2017

Previous studies determined that shear stress imposed on bovine aortic endothelial cell (BAEC) monolayers increased the hydraulic conductivity ( LP); however, the mechanism by which shear stress increases LPremains unknown. This study tested the hypothesis that shear stress regulates paracellular transport by altering the expression and phosphorylation state of the tight junction protein occludin. The effect of shear stress on occludin content was examined by Western blot analysis. Ten dyn/cm2significantly reduced occludin content in a time-dependent manner such that after a 3 h exposure to shear, occludin content decreased to 44% of control. Twenty dyn/cm2decreased occludin content to 50% of control and increased LPby 4.7-fold after 3 h. Occludin expression and LPdepend on tyrosine kinase activity because erbstatin A (10 μM) attenuated both the shear-induced decrease in occludin content and increase in LP. Shear stress increased occludin phosphorylation after 5 min, 15 min, and 3 h exposures. The shear-induced increase in occludin phosphorylation was attenuated with dibutyryl (DB) cAMP (1 mM), a reagent previously shown to reverse the shear-induced increase in LP. We conclude that shear stress rapidly (≤5 min) increases occludin phosphorylation and significantly decreases the expression of occludin over 1–4 h. Alterations in the occludin phosphorylation state and occludin total content are potential mechanisms by which shear stress increases LP.
Regulation of ERK phosphorylation in differentiated arterial muscle of rabbits
Authors: Ratz Paul H.
Published: December 2017

Extracellular signal-regulated kinases (ERK) and mitogen-activated protein (MAP) kinases participate in cell signaling, regulating cell growth. In differentiated cells, the role ERK plays is less well known. This study quantified the degree of basal and stimulated ERK phosphorylation and contraction in freshly isolated arteries. The level of basal ERK phosphorylation was identical in preloaded and slack arteries, was greater in media than in the whole artery, and was reduced by the MAP or ERK kinase (MEK) inhibitor PD-98059. Chemical denudation using 1 H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one did not elevate basal ERK phosphorylation. PD-98059 reduced maximum phenylephrine (PE)-stimulated ERK phosphorylation but not force. Pervanadate elevated ERK phosphorylation without causing contraction. Contractions produced by PE and relaxations produced by PE washout preceded the ERK phosphorylation. K+depolarization, muscle stretch, and angiotensin II elevated ERK phosphorylation transiently, whereas PE maintained ERK phosphorylation for 30 min. The α1A-adrenergic receptor antagonist WB-4101 reduced PE-stimulated force by 70% and abolished PE-induced ERK phosphorylation. Afterloaded and zero-load contractions produced by K+depolarization displayed identical increases in ERK phosphorylation. These data indicate that ERK was active basally in the differentiated artery but regulated by the endothelium and that ERK phosphorylation was not load dependent. A strong correlation between PE-induced force and ERK phosphorylation supports the hypothesis that ERK activation may reflect a signal “notifying” the cell of the degree of α1-adrenergic receptor-induced contraction.
Pregnancy enhances endothelium-dependent relaxation of ovine uterine artery: role of NO and intracellular Ca2+
Authors: Xiao Daliao , Pearce William J. , Zhang Lubo
Published: December 2017

The present study tested the hypothesis that the pregnancy-associated increase in endothelium-dependent relaxation of the uterine artery was mediated primarily by an increase in nitric oxide (NO) release, resulting in a reduction in smooth muscle intracellular Ca2+concentration ([Ca2+]i). Uterine arteries obtained from nonpregnant and near-term (140 days gestation) pregnant sheep were used. The Ca2+ionophore A23187 induced endothelium-dependent relaxations in both nonpregnant and pregnant uterine arteries, with an increased relaxation in the pregnant tissue. In contrast, endothelium-independent relaxations induced by sodium nitroprusside were the same in nonpregnant and pregnant arteries. In addition, removal of the endothelium significantly increased noradrenaline-induced contractions in pregnant, but not nonpregnant, uterine arteries. In accordance, pregnancy increased both basal and A23187 -stimulated NO releases in the uterine artery. Simultaneous measurement of tension and [Ca2+]iin the smooth muscle demonstrated a linear correlation with the slope of unity between A23187 -induced relaxation and the reduction of [Ca2+]iin both nonpregnant and pregnant uterine arteries. The A23187 -induced reduction of [Ca2+]iwas significantly enhanced in pregnant, compared with nonpregnant, uterine arteries. The results indicate that pregnancy increases NO release, which, through decreasing [Ca2+]iin the smooth muscle, accounts for the increased endothelium-dependent relaxation of the uterine artery. Signal transduction pathways distal to NO production are not changed by pregnancy.
Ca2+-activated K+ channels modulate basal and E2β-induced rises in uterine blood flow in ovine pregnancy
Authors: Rosenfeld Charles R. , Cornfield David N. , Roy Timothy
Published: December 2017

Uterine blood flow (UBF) increases >30-fold during ovine pregnancy. During the last trimester, this reflects vasodilation, which may be due to placentally derived estrogens. In nonpregnant ewes, estradiol-17β (E2β) increases UBF >10-fold by activating nitric oxide synthase and large conductance calcium-dependent potassium channels (BKCa). To determine whether BKCa channels modulate basal and E2β-induced increases in UBF, studies were performed in near-term pregnant ewes with uterine artery flow probes and catheters for intra-arterial infusions of tetraethylammonium (TEA), a selective BKCa channel antagonist at <1 mM, in the absence or presence of E2β (1 μg/kg iv). Uterine arteries were collected to measure BKCa channel mRNA. TEA (0.15 mM) decreased basal UBF ( P < 0.0001) 40 ± 8% and 55 ± 7% ( n = 11) at 60 and 90 min, respectively, and increased resistance 175 ± 48% without affecting ( P > 0.1) mean arterial pressure (MAP), heart rate, or contralateral UBF. Systemic E2β increased UBF 30 ± 6% and heart rate 13 ± 1% ( P ≤ 0.0001, n = 13) without altering MAP. Local TEA (0.15 mM) inhibited E2β-induced increases in UBF without affecting increases in heart rate (10 ± 4%; P = 0.006). BKCa channel mRNA was present in uterine artery myocytes from pregnant and nonpregnant ewes. Exponential increases in ovine UBF in late pregnancy may reflect BKCa channel activation, which may be mediated by placentally derived estrogens.
O2release from erythrocytes flowing in a narrow O2-permeable tube: effects of erythrocyte aggregation
Authors: Tateishi Norihiko , Suzuki Yoji , Cicha Iwona , Maeda Nobuji
Published: December 2017

The effects of erythrocyte aggregation on O2release were examined using O2-permeable fluorinated ethylenepropylene copolymer tubes (inner diameter, 25 μm; outer diameter, 100 μm). Measurements were performed using an apparatus built on an inverted microscope that contained a scanning-grating spectrophotometer with a photon count detector connected to two photomultipliers and an image processor through a video camera. The rate of O2release from the cells flowing in the narrow tube was determined based on the visible absorption spectrum and the flow velocity of the cells as well as the tube size. When the tube was exposed to nitrogen-saturated deoxygenated saline containing 10 mM sodium dithionite, the flowing erythrocytes were deoxygenated in proportion to the traveling distance, and the deoxygenation at a given distance increased with decreasing flow velocity and cell concentration (hematocrit). Adding Dextran T-70 to the cell suspension increased erythrocyte aggregation in the tube, which resulted in suppressed cell deoxygenation and increased marginal cell-free-layer thickness. The deoxygenation was inversely proportional to the cell-free-layer thickness. The relation was not essentially altered even when the medium viscosity was adjusted with Dextran T-40 to remain constant. The rate of O2release from erythrocytes in the tube was discussed in relation to the O2diffusion process. We conclude that the diffusion of O2from erythrocytes flowing in narrow tubes is inhibited primarily by erythrocyte aggregation itself and partly by thickening of the cell-free layer.
Expression of metabotropic glutamate receptors in nodose ganglia and the nucleus of the solitary tract
Authors: Hoang Caroline J. , Hay Meredith
Published: December 2017

The purpose of this study was to identify the complement of metabotropic glutamate receptors (mGluRs) expressed in nodose ganglia and the nucleus tractus solitarius (NTS). mRNA from these tissues was isolated and amplified with standard RT-PCR with primers specific for each mGluR subtype. The results of this analysis showed that the NTS expresses all eight mGluR subtypes, whereas nodose ganglia express only group III mGluRs: mGluR4, mGluR6, mGluR7, and mGluR8. Application of the group III-specific mGluR agonistl-(+)-2-amino-4-phosphonobutyric acid (100 μM) reversibly inhibited voltage-gated calcium currents isolated from DiI-labeled aortic baroreceptor neurons and unlabeled nodose neurons. The results of this study suggest that group III mGluRs are the primary mGluR subtype expressed in visceral afferent neurons and that these receptors may be involved in afferent central transmission.
Selective A2Aadenosine receptor activation reduces skin pressure ulcer formation and inflammation
Authors: Peirce Shayn M. , Skalak Thomas C. , Rieger Jayson M. , Macdonald Timothy L. , Linden Joel
Published: December 2017

Activation of A2Aadenosine receptors (A2A-AR) by ATL-146e (formerly DWH-146e) prevents inflammatory cell activation and adhesion. Recurrent ischemia-reperfusion (I/R) of the skin results in pressure ulcer formation, a major clinical problem. ATL-146e was evaluated in a novel reproducible rat model of pressure ulcer. A 9-cm2region of dorsal rat skin was cyclically compressed at 50 mmHg using a surgically implanted metal plate and an overlying magnet to generate reproducible tissue necrosis. Osmotic minipumps were implanted into 24 rats divided into four equal groups to infuse vehicle (control), ATL-146e (0.004 μg · kg−1· min−1), ATL-146e plus an equimolar concentration of A2Aantagonist, ZM-241385, or ZM-241385 alone. Each group received 10 I/R cycles. In non-I/R-treated skin, ATL-146e has no effect on blood flow. I/R-treated skin of the ATL-146e group compared with the vehicle group had 65% less necrotic area, 31% less inhibition of average skin blood flow, and fewer extravasated leukocytes (23 ± 3 vs. 49 ± 6 per 500 μm2). These data suggest that ATL-146e, acting via an A2A-AR, reduces leukocyte infiltration and is a potent prophylactic for I/R injury in skin.
Motion of red blood cells in a capillary with an endothelial surface layer: effect of flow velocity
Authors: Secomb T. W. , Hsu R. , Pries A. R.
Published: December 2017

Interior surfaces of capillaries are lined with macromolecules forming an endothelial surface layer (ESL). A theoretical model is used to investigate effects of flow velocity on motion and axisymmetric deformation of red blood cells in a capillary with an ESL. Cell deformation is analyzed, including effects of membrane shear and bending elasticity. Plasma flow around the cell and through the ESL is computed using lubrication theory. The ESL is represented as a porous layer that exerts compressive forces on red blood cells that penetrate it. According to the model, hydrodynamic pressures generated by plasma flow around the cell squeeze moving red blood cells into narrow elongated shapes. If the ESL is 0.7 μm wide, with hydraulic resistivity of 2 × 108dyn · s · cm−4, and exerts a force of 20 dyn/cm2, predicted variation with flow velocity of the gap width between red blood cell and capillary wall agrees well with observations. Predicted gap at a velocity of 0.1 mm/s is ∼0.6 μm vs. ∼0.2 μm with no ESL. Predicted flow resistance increases markedly at low velocities. The model shows that exclusion of red blood cells from the ESL in flowing capillaries can result from hydrodynamic forces generated by plasma flow through the ESL.
Larger late sodium conductance in M cells contributes to electrical heterogeneity in canine ventricle
Authors: Zygmunt Andrew C. , Eddlestone Geoffrey T. , Thomas George P. , Nesterenko Vladislav V. , Antzelevitch Charles
Published: December 2017

Action potentials and whole cell sodium current were recorded in canine epicardial, midmyocardial, and endocardial myocytes in normal sodium at 37°C. Tetrodotoxin (TTX) reduced the action potential duration of midmyocardial cells to a greater degree than either epicardial or endocardial cells. Whole cell recordings in potassium-free and very-low-chloride solutions revealed a slowly decaying current that was completely inhibited by 5 μM TTX or replacement of external and internal sodium with the impermeant cation N-methyl-d-glucamine. Late sodium current density at 0 mV was 47% greater in midmyocardial cells and averaged −0.532 ± 0.058 pA/pF in endocardial, −0.463 ± 0.068 pA/pF in epicardial, and −0.785 ± 0.070 pA/pF in midmyocardial cells. Neither the frequency dependence of late sodium current nor its recovery from inactivation exhibited transmural differences. After a 4.5-s pulse to −30 mV, late sodium current recovered with a single time constant of 140 ms. We conclude that a larger late sodium conductance in midmyocardial cells will favor longer action potentials in these cells. More importantly, drugs that slow inactivation of sodium channels will produce a nonuniform response across the ventricular wall that is proarrhythmic.
Quantification of 3-D regional myocardial deformation: shape-based analysis of magnetic resonance images
Authors: Sinusas Albert J. , Papademetris Xenophon , Constable R. Todd , Dione Donald P. , Slade Martin D. , Shi Pengcheng , Duncan James S.
Published: December 2017

A comprehensive three-dimensional (3-D) shape-based approach for quantification of regional myocardial deformations was evaluated in a canine model ( n = 8 dogs) with the use of cine magnetic resonance imaging. The shape of the endocardial and epicardial surfaces was used to track the 3-D trajectories of a dense field of points over the cardiac cycle. The shape-based surface displacements are integrated with a continuum biomechanics model incorporating myofiber architecture to estimate both cardiac- and fiber-specific endocardial and epicardial strains and shears for 24 left ventricular regions. Whereas radial and circumferential end-systolic strains were fairly uniform, there was a significant apex-to-base gradient in longitudinal strain and radial-longitudinal shear. We also observed transmural epicardial-to-endocardial gradients in both cardiac- and fiber-specific strains. The increase in endocardial strain was accompanied by increases in radial-longitudinal shear and radial-fiber shears in the endocardium, supporting previous theories of regional myocardial deformation that predict considerable sliding between myocardial fibers.
Differences in the dynamic cerebrovascular response between stepwise up tilt and down tilt in humans
Authors: Sato Jiro , Tachibana Masatoshi , Numata Tsutomu , Nishino Takashi , Konno Akiyoshi
Published: December 2017

We studied dynamic cerebrovascular responses in eight healthy humans during repetitive stepwise upward tilt (SUT) and stepwise downward tilt (SDT) maneuvers between supine and 70° standing at intervals of 60 s. Mean cerebral blood flow velocity (FVMCA) was measured at the middle cerebral artery (MCA) with transcranial Doppler ultrasonography. Mean arterial blood pressure (ABP) was measured via the radial artery and adjusted at the level of the MCA (ABPMCA). Cerebral critical closing pressure (PCC) was estimated from the systolic-diastolic relationship between FVMCA and ABPMCA. ABPMCA minus PCC was considered the cerebral perfusion pressure (CPP). The tilt maneuvers produced stepwise changes in both CPP and FVMCA. The FVMCA response to SUT was well characterized by a linear second-order model. However, that to SDT presented a biphasic behavior that was described significantly better ( P < 0.05) by the addition of a slowly responding component to the second-order model. This difference may reflect both different cardiovascular responses to SUT or SDT and different cerebrovascular autoregulatory behaviors in response to decreases or increases in CPP.
Effects of erythrocyte aggregation and venous network geometry on red blood cell axial migration
Authors: Bishop Jeffrey J. , Popel Aleksander S. , Intaglietta Marcos , Johnson Paul C.
Published: December 2017

Axial migration of red blood cells in small glass tubes can cause blood viscosity to be effectively independent of shear rate. However, this phase separation may not occur to the same degree in the venous network due to infusion of cells and aggregates at branch points. To investigate this hypothesis, we followed trajectories of fluorescently labeled red blood cells in the venular network of the rat spinotrapezius muscle at normal and reduced flow with and without red blood cell aggregation. Cells traveling near the wall of an unbranched venular segment migrated ∼1% of the longitudinal path length without aggregation and migrated slightly more with aggregation. Venular segment length between branch points averaged three to five times the diameter. Cells in the main vessel were shifted centrally by up to 20% of diameter at branch points, reducing the migration rate of cells near the opposite wall to <1% even in the presence of aggregation. We conclude that formation of a cell-free marginal layer in the venular network is attenuated due to the time dependence of axial migration and the frequent branching of the network.
Triglycerides impair postischemic recovery in isolated hearts: roles of endothelin-1 and trimetazidine
Authors: Monti Lucilla D. , Allibardi Sonia , Piatti Pier Marco , Valsecchi Gianpietro , Costa Sabrina , Pozza Guido , Chierchia Sergio , Samaja Michele
Published: December 2017

There is growing evidence that hypertriglyceridemia exacerbates ischemic injury. We tested the hypothesis that triglycerides impair myocardial recovery from low-flow ischemia in an ex vivo model and that such an effect is related to endothelin-1. Hyperglycemic (glucose concentration = 12 mmol/l) and hyperinsulinemic (insulin concentration = 1.2 μmol/l) isolated rat hearts were perfused with Krebs-Henseleit buffer (Po2= 670 mmHg, pH 7.4, 37°C) added with increasing triglycerides (0, 1,000, 2,000, and 4,000 mg/dl, n = 6–9 rats/group). Hearts were exposed to 60 min of low-flow ischemia (10% of basal coronary flow), followed by 30 min of reperfusion. We found that increasing triglycerides impaired both the diastolic ( P< 0.005) and systolic ( P < 0.02) recovery. The release of endothelin-1 during reperfusion increased linearly with triglyceride concentration ( P = 0.0009). Elevated triglycerides also increased the release of nitrite and nitrate (NOx), the end products of nitric oxide, up to 6 μmol/min. Trimetazidine (1 μmol) further increased NOxrelease, blunted endothelin-1 release, and protected myocardial function during recovery. We conclude that high triglyceride levels impair myocardial recovery after low-flow ischemia in association with endothelin-1 release. The endothelium-mediated effect of triglycerides on both contractile recovery and endothelin-1 release is prevented by 1 μM trimetazidine.
Hindlimb unweighting affects rat vascular capacitance function
Authors: Dunbar Stacey L. , Tamhidi Laleh , Berkowitz Dan E. , Shoukas Artin A.
Published: December 2017

Microgravity is associated with an impaired stroke volume and, therefore, cardiac output response to orthostatic stress. We hypothesized that a decreased venous filling pressure due to increased venous compliance may be an important contributing factor in this response. We used a constant flow, constant right atrial pressure cardiopulmonary bypass procedure to measure total systemic vascular compliance (CT), arterial compliance (CA), and venous compliance (CV) in seven control and seven 21-day hindlimb unweighted (HLU) rats. These compliance values were calculated under baseline conditions and during an infusion of 0.2 μg · kg−1 · min−1norepinephrine (NE). The change in reservoir volume, which reflects changes in unstressed vascular volume (ΔV0) that occurred upon infusion of NE, was also measured. CT and CV were larger in HLU rats both at baseline and during the NE infusion ( P < 0.05). Infusion of NE decreased CT and CV by ∼20% in both HLU and control rats ( P < 0.01). CA was also significantly decreased in both groups of rats by NE ( P < 0.01), but values of CA were similar between HLU and control rats both at baseline and during the NE infusion. Additionally, the NE-induced ΔV0 was attenuated by 53% in HLU rats compared with control rats ( P < 0.05). The larger CV and attenuated ΔV0 in HLU rats could contribute to a decreased filling pressure during orthostasis and thus may partially underlie the mechanism leading to the exaggerated fall in stroke volume and cardiac output seen in astronauts during an orthostatic stress after exposure to microgravity.
Shear level influences resistance artery remodeling: wall dimensions, cell density, and eNOS expression
Authors: Tuttle Jay L. , Nachreiner Ryan D. , Bhuller Amardip S. , Condict Kevin W. , Connors Bret A. , Herring B. Paul , Dalsing Michael C. , Unthank Joseph L.
Published: December 2017

The magnitude of shear stimulus has been shown to determine the level of growth factor expression in cell culture. However, little is known regarding what effect shear level has on specific arterial wall remodeling events in vivo. We have hypothesized that the rate of luminal diameter change and specific remodeling events within the arterial wall layers are dependent on shear level. Selective ligations were made to alter the number of microvascular perfusion units of mesenteric arteries within the same animal to ∼50%, 200%, and 400% of control. Arterial blood flow and wall shear rate were correlated with the degree of alteration in perfusion units. Luminal diameters were decreased in 50% arteries by day 2 and increased ∼17% and 33%, respectively, in 200% and 400% arteries at day 7. The rate of diameter change was greatest in 50% and 400% arteries. Wall areas (medial +37%; intimal +18% at day 2) and cell densities (intimal +26%; adventitial +44% at day 2) were altered only in the 400% arteries. A positive correlation existed by day 2between endothelial staining for endothelial nitric oxide synthase and shear level. The results demonstrate that shear level influences the rate of luminal expansion, specific remodeling events within each wall layer, and the degree of endothelial gene expression. A greater understanding of how shear level influences specific remodeling events within each wall layer should aid in the development of targeted therapies to manipulate the remodeling process in health and disease.
Effect of estrogen replacement therapy on distribution of myocardial blood flow in female anesthetized rabbits
Authors: Rouleau J. R. , Dagnault A. , Simard D. , Lavallée B. , Bélanger A. , Blouin A. , Kingma J. G.
Published: December 2017

Estrogen replacement therapy reduces risk of cardiovascular events by altering coronary vasoregulation and distribution of blood flow. Vessel reactivity and blood flow distribution were assessed in anesthetized female rabbits in the following groups: 1) sham, 2) ovariectomy, 3) ovariectomy + 17β-estradiol, and 4) ovariectomy + dehydroepiandrosterone. After a 2-wk treatment, cardiac hemodynamics, vascular reserve, and blood flow were evaluated during the following infusions: 1) NaCl, or vehicle (0.5 ml/min), 2) acetylcholine (2 mg/kg), 3) isoproterenol (2 mg · kg−1 · min−1), and 4) chromonar (8 mg/kg). In hearts from ovariectomized rabbits, autoregulatory blood flow was preserved despite lower diastolic perfusion pressures (55 ± 8 vs. 64 ± 8 mmHg in sham) and rate-pressure product (14.4 ± 0.8 vs. 19.3 ± 0.8 beats/min · mmHg×10−3). Estrogen replacement therapy restored coronary pressure and reserve, and all drugs increased vascular conductance. In conclusion, in hearts from ovariectomized rabbits, vascular reserve declined because coronary pressure was lower; however, blood flow was preserved at a higher level than expected for oxygen demand. Estrogen replacement therapy restores myocardial oxygen supply-demand indices and returns coronary pressure-flow data to levels observed in animals with intact ovaries.
Cerebral arteriolar structure and function in pinealectomized rats
Authors: Régrigny Olivier , Dupuis François , Atkinson Jeffrey , Limiñana Patrick , Scalbert Elizabeth , Delagrange Philippe , Chillon Jean-Marc
Published: December 2017

We examined cerebral arteriolar structure and autoregulation of cerebral blood flow (CBF) in control ( n = 8), sham-operated ( n = 8), pinealectomized ( n = 10), and pinealectomized plus melatonin-treated (0.51 ± 0.01 mg · kg−1 · day−1 in drinking water, n = 9) young Wistar rats. The lower limit of CBF autoregulation (LLCBF) was determined by measurement of CBF (in arbitrary units, laser Doppler) during stepwise hypotensive hemorrhage; the arteriolar internal diameter (ID; in μm, cranial window) was also measured. Measurements of ID were repeated during a second stepwise hypotension after smooth muscle cell deactivation (67 mmol/l EDTA). The cross-sectional area (CSA) was measured by histometry. CSA and EDTA-induced vasodilatation decreased after pinealectomy (517 ± 21 vs. 819 ± 40 μm2 in sham and 829 ± 55 μm2 in control, P < 0.05, and 81 ± 4 vs. 102 ± 5 μm in sham and 104 ± 4 μm in control, P < 0.05, respectively) and were restored by melatonin (924 ± 39 μm2 and 102 ± 5 μm, respectively). These results suggest that melatonin deprival makes the arteriolar wall thinner and stiffer. However, these changes had little effect on LLCBF. In conclusion, pinealectomy of young rats induces atrophy and decreases distensibility of the cerebral arteriolar wall; these effects are prevented by melatonin. They do not modify LLCBF.
Role of sarcoplasmic reticulum in regulation of tonic contraction of rabbit basilar artery
Authors: Szado Tania , McLarnon Megan , Wang Xiaodong , van Breemen Casey
Published: December 2017

Superficial sarcoplasmic reticulum (SR) regulates smooth muscle force development directly by Ca2+ release and removal to and from the cytoplasm (Somlyo and Somlyo. J Cardiovasc Pharmacol 8, Suppl8: S42–S47, 1986) by buffering Ca2+ influx and contributing to Ca2+ extrusion (Mueller and van Breemen. Nature 281: 682–683, 1979) and indirectly by releasing Ca2+ near Ca2+-activated K+channels (KCa) to hyperpolarize the plasma membrane (Bolton and Imaizumi. Cell Calcium 20: 141–152, 1996 and Nelson et al. Science 270: 633–637, 1995). In the rabbit basilar artery, relative contributions of direct effects and those mediated through activation of KCa were evaluated by measuring force and intracellular Ca2+ concentration ([Ca2+]i) in response to the SR-depleting agents thapsigargin and ryanodine and the large conductance KCa (BKCa) blockers iberiotoxin (IbTX) and tetraethylammonium ion (TEA). A large contraction was observed in response to KCa blockade with either 3 mM TEA or 100 nM IbTX and also after addition of 10 μM ryanodine or 2 μM thapsigargin. When KCa was blocked first with TEA or IbTX, subsequent addition of thapsigargin or ryanodine also increased force. Measurements of fura 2 fluorescence showed parallel increases in [Ca2+]i in response to sequential blockade of sarco(endo)plasmic reticulum Ca2+-ATPase and KCa regardless of the order of application. It appears that a significant fraction of KCa remains activated in the absence of SR function and that SR contributes to relaxation after blockade of KCa. We found that depletion of SR before stimulating Ca2+ influx through voltage-gated Ca2+ channels markedly reduced force development rate and that thapsigargin abolished this effect. We conclude that the SR of rabbit cerebral arteries modulates constriction by direct and indirect mechanisms.
Selective AV nodal vagal stimulation improves hemodynamics during acute atrial fibrillation in dogs
Authors: Wallick Don W. , Zhang Youhua , Tabata Tomotsugu , Zhuang Shaowei , Mowrey Kent A. , Watanabe Junko , Greenberg Neil L. , Grimm Richard A. , Mazgalev Todor N.
Published: December 2017

Although the atrioventricular node (AVN) plays a vital role in blocking many of the atrial impulses from reaching the ventricles during atrial fibrillation (AF), a rapid irregular ventricular rate nevertheless persists. The goals of the present study were to explore the feasibility of novel epicardial selective vagal nerve stimulation for slowing of the ventricular rate during AF and to characterize the hemodynamic benefits in vivo. Electrophysiological-echocardiographic experiments were performed on 11 anesthetized open-chest dogs. Hemodynamic measurements were performed during three distinct periods: 1) sinus rate, 2) AF, and 3) AF with vagal nerve stimulation. AF was associated with significant deterioration of all measured parameters ( P < 0.025). The vagal nerve stimulation produced slowing of the ventricular rate, significant reversal of the pressure and contractile indexes ( P < 0.025), and a sharp reduction in one-half of the abortive ventricular contractions. The present study provides comprehensive evidence that slowing of the ventricular rate during AF by selective ganglionic stimulation of the vagal nerves that innervate the AVN successfully improved the hemodynamic responses.
Ischemic and anesthetic preconditioning reduces cytosolic [Ca2+] and improves Ca2+responses in intact hearts
Authors: An Jianzhong , Varadarajan Srinivasan G. , Novalija Enis , Stowe David F.
Published: December 2017

Ca+loading during reperfusion after myocardial ischemia is linked to reduced cardiac function. Like ischemic preconditioning (IPC), a volatile anesthetic given briefly before ischemia can reduce reperfusion injury. We determined whether IPC and sevoflurane preconditioning (SPC) before ischemia equivalently improve mechanical and metabolic function, reduce cytosolic Ca2+loading, and improve myocardial Ca2+responsiveness. Four groups of guinea pig isolated hearts were perfused: no ischemia, no treatment before 30-min global ischemia and 60-min reperfusion (control), IPC (two 2-min occlusions) before ischemia, and SPC (3.5 vol%, two 2-min exposures) before ischemia. Intracellular Ca2+concentration ([Ca2+]i) was measured at the left ventricular (LV) free wall with the fluorescent probe indo 1. Ca2+responsiveness was assessed by changing extracellular [Ca2+]. In control hearts, initial reperfusion increased diastolic [Ca2+] and diastolic LV pressure (LVP), and the maximal and minimal derivatives of LVP (dLVP/d tmaxand dLVP/d tmin, respectively), O2consumption, and cardiac efficiency (CE). Throughout reperfusion, IPC and SPC similarly reduced ischemic contracture, ventricular fibrillation, and enzyme release, attenuated rises in systolic and diastolic [Ca2+], improved contractile and relaxation indexes, O2consumption, and CE, and reduced infarct size. Diastolic [Ca2+] at 50% dLVP/d tminwas right shifted by 32–53 ± 8 nM after 30-min reperfusion for all groups. Phasic [Ca2+] at 50% dLVP/d tmaxwas not altered in control but was left shifted by −235 ± 40 nM [Ca2+] after IPC and by −135 ± 20 nM [Ca2+] after SPC. Both SPC and IPC similarly reduce Ca2+loading, while augmenting contractile responsiveness to Ca2+, improving postischemia cardiac function and attenuating permanent damage.
Distribution spaces for hyaluronan and albumin in rat tail tendons
Authors: Aukland Knut , Tenstad Olav , Wiig Helge
Published: December 2017

A low concentration of hyaluronan (HA) in lymph compared with tissue suggests a large bound fraction. To investigate the distribution and mobility of HA and serum albumin (Alb), we eluted the rat tail tendon with a series of l5 successive centrifugations, each preceded by the addition of 0.15 M NaCl (15% of initial wet wt). The eluate concentration fell exponentially versus the accumulated eluate, allowing estimation of the maximal elutable amount (EHAand EAlb). Alb elution was practically complete from a space of ≈28% of wet wt at all centrifugation rates. Twenty percent of HA was elutable at 500 rpm, apparently from the same space as Alb, increasing to 40% at >4,000 rpm. This pattern was not significantly influenced by using 2 M NaCl or by the addition of plasma or metabolic inhibitors. Without prehydration and centrifugation at high revolutions per minute, both Alb and HA concentrations fell rapidly toward zero, presumably in part reflecting mobilization of HA- and Alb-free fluid from the collagen intrafibrillar space (3). We conclude that with prehydration the fibrils swell, increasing the intramolecular spaces to become “penetrable” to HA and allowing removal of HA-containing fluid when the fibrils are compressed by the next centrifugation at high revolutions per minute, increasing EHAfrom 23 to 45%. Chemical binding presumably explains the unelutable 55% of tendon HA. Intrafibrillar HA may act to stabilize the fibrillar volume.
Important role of energy-dependent mitochondrial pathways in cultured rat cardiac myocyte apoptosis
Authors: Shiraishi Jun , Tatsumi Tetsuya , Keira Natsuya , Akashi Kazuko , Mano Akiko , Yamanaka Satoshi , Matoba Satoaki , Asayama Jun , Yaoi Takeshi , Fushiki Shinji , Fliss Henry , Nakagawa Masao
Published: December 2017

Recent studies have suggested that apoptosis and necrosis share common features in their signaling pathway and that apoptosis requires intracellular ATP for its mitochondrial/apoptotic protease-activating factor-1 suicide cascade. The present study was, therefore, designed to examine the role of intracellular energy levels in determining the form of cell death in cardiac myocytes. Neonatal rat cardiac myocytes were first incubated for 1 h in glucose-free medium containing oligomycin to achieve metabolic inhibition. The cells were then incubated for another 4 h in similar medium containing staurosporine and graded concentrations of glucose to manipulate intracellular ATP levels. Under ATP-depleting conditions, the cell death caused by staurosporine was primarily necrotic, as determined by creatine kinase release and nuclear staining with ethidium homodimer-1. However, under ATP-replenishing conditions, staurosporine increased the percentage of apoptotic cells, as determined by nuclear morphology and DNA fragmentation. Caspase-3 activation by staurosporine was also ATP dependent. However, loss of mitochondrial transmembrane potential (ΔΨm), Bax translocation, and cytochrome crelease were observed in both apoptotic and necrotic cells. Moreover, cyclosporin A, an inhibitor of mitochondrial permeability transition, attenuated staurosporine-induced apoptosis and necrosis through the inhibition of ΔΨmreduction, cytochrome c release, and caspase-3 activation. Our data therefore suggest that staurosporine induces cell demise through a mitochondrial death signaling pathway and that the presence of intracellular ATP favors a shift from necrosis to apoptosis through caspase activation.
Theslow momutation reduces pacemaker current and heart rate in adult zebrafish
Authors: Warren Kerri S. , Baker Keith , Fishman Mark C.
Published: December 2017

Genetic studies in zebrafish have focused on embryonic mutations, but many physiological mechanisms continue to mature after embryogenesis. We report here that zebrafish homozygous for the mutation slow mo can be raised to adulthood. In the embryo, the slow mo gene is needed to regulate heart rate, and its mutation causes a reduction in pacemaker current ( Ih) and slowing of heart rate (bradycardia). The homozygous adult slow mo fish continues to manifest bradycardia, without other evident ill effects. Patch-clamp analysis of isolated adult cardiomyocytes reveals that Ihhas chamber-specific properties such that the atrial current density of Ihis far greater than the ventricular current density of Ih. Ihis markedly diminished in cardiomyocytes from both chambers of slow mo mutant fish. Thus Ihcontinues to be a critical determinant of pacemaker rate even after adult neural and humoral influences have developed. It is clear that zebrafish may be used for genetic dissection of selected physiological mechanisms in the adult.