bluuebunny/crossref_metadata_2025 huggingface dataset:
Endothelial cell regrowth and morphology after balloon catheter injury of alloxan-induced diabetic rabbits
Authors: Schiller Natalie K. , Timothy Alvin M. , Chen I.-L. , Rice Janet C. , Akers Donald L. , Kadowitz Philip J. , McNamara Dennis B.
Published: December 2017

Neointimal thickening after catheter injury has been reported to be influenced by the integrity of the vascular endothelium. We have previously shown that neointimal thickening is significantly reduced in alloxan-induced diabetic New Zealand White rabbits after catheter injury compared with euglycemic rabbits. In the present study, it was hypothesized that endothelial cell regrowth, morphology, and endothelium-dependent vasoreactivity after catheter injury are improved in the diabetic rabbit (glucose ≥400 mg/dl) compared with the euglycemic rabbit. Two weeks after catheter injury, the percent endothelial regrowth was significantly increased in diabetic animals compared with euglycemic animals (32.1 ± 2 and 15.6 ± 1, respectively; P < 0.05). The endothelial cell morphology analyzed by scanning electron microscopy was also restored 2 wk after catheter injury in thoracic aortas from the diabetic animals compared with vessels from euglycemic animals. Endothelium-dependent relaxation to ACh in vessels from diabetic and euglycemic rabbits was attenuated 2 wk after injury, and, although improved by 4 and 8 wk, relaxation remained significantly depressed. These results suggest that endothelial cell regrowth and morphology in diabetic animals was improved compared with euglycemic animals; however, endothelium-dependent vasoreactivity remained impaired. Thus the attenuated neointimal thickening seen in the diabetic rabbit may be a function of the rate and degree of regrowth rather than the normalization of ACh-induced relaxation.
Cerebral desaturation during exercise reversed by O2 supplementation
Authors: Nielsen H. B. , Boushel R. , Madsen P. , Secher N. H.
Published: December 2017

The combined effects of hyperventilation and arterial desaturation on cerebral oxygenation ([Formula: see text]) were determined using near-infrared spectroscopy. Eleven competitive oarsmen were evaluated during a 6-min maximal ergometer row. The study was randomized in a double-blind fashion with an inspired O2 fraction of 0.21 or 0.30 in a crossover design. During exercise with an inspired O2 fraction of 0.21, the arterial CO2 pressure (35 ± 1 mmHg; mean ± SE) and O2 pressure (77 ± 2 mmHg) as well as the hemoglobin saturation (91.9 ± 0.7%) were reduced ( P < 0.05).[Formula: see text] was reduced from 80 ± 2 to 63 ± 2% ( P < 0.05), and the near-infrared spectroscopy-determined concentration changes in deoxy- (ΔHb) and oxyhemoglobin (ΔHbO2) of the vastus lateralis muscle increased 22 ± 3 μM and decreased 14 ± 3 μM, respectively ( P < 0.05). Increasing the inspired O2fraction to 0.30 did not affect ventilation (174 ± 4 l/min), but arterial CO2 pressure (37 ± 2 mmHg), O2 pressure (165 ± 5 mmHg), and hemoglobin O2saturation (99 ± 0.1%) increased ( P < 0.05).[Formula: see text] remained close to the resting level during exercise (79 ± 2 vs. 81 ± 2%), and although the muscle ΔHb (18 ± 2 μM) and ΔHbO2 (−12 ± 3 μM) were similar to those established without O2 supplementation, work capacity increased from 389 ± 11 to 413 ± 10 W ( P < 0.05). These results indicate that an elevated inspiratory O2fraction increases exercise performance related to maintained cerebral oxygenation rather than to an effect on the working muscles.
Calcium-calmodulin mediates bradykinin-induced MAPK phosphorylation and c-fosinduction in vascular cells
Authors: Naidu Padma S. , Velarde Victoria , Kappler Christiana S. , Young Roger C. , Mayfield Ronald K. , Jaffa Ayad A.
Published: December 2017

The vasoactive peptide bradykinin (BK) has been implicated in the pathophysiology of a number of vascular wall abnormalities, but the cellular mechanisms by which BK generates second messengers that alter vascular function are as yet undefined. Exposure of vascular smooth muscle cells (VSMC) to BK (10−7M) produced a rapid and transient rise in intracellular calcium, which preceded an increase in tyrosine phosphorylation of mitogen-activated protein kinase (MAPK). MAPK activation by BK was observed as early as 1 min, peaked at 5 min, and returned to baseline by 20 min. Treatment of cells with the intracellular calcium chelator EGTA-acetoxymethyl ester inhibited BK-stimulated MAPK activation, suggesting that intracellular calcium mobilization contributes to the activation of MAPK. The calmodulin inhibitor W-7 also markedly inhibited BK-induced MAPK phosphorylation in the cytoplasm as well as in the nucleus. Moreover, the BK-induced increase in c- fos mRNA levels was significantly inhibited by the calmodulin inhibitor, indicating that calmodulin is required for BK signaling leading to c- fos induction. These results implicate the calcium-calmodulin pathway in the mechanisms for regulating MAPK activity and the resultant c- fos expression induced by BK in VSMC.
Cycloheximide rapidly inhibits cortical COX activity and COX-dependent pial arteriolar dilation in piglets
Authors: Domoki Ferenc , Perciaccante James V. , Veltkamp Roland , Robins Greg , Bari Ferenc , Louis Thomas M. , Busija David W.
Published: December 2017

We have previously shown that cycloheximide (CHX) preserved neuronal function after global cerebral ischemia in piglets, in a manner similar to indomethacin. To elucidate the mechanism of this protection, we tested the hypothesis that CHX would inhibit cyclooxygenase (COX) activity in the piglet cerebral cortex and vasculature. Pial arteriolar responses to hypercapnia, arterial hypotension, and sodium nitroprusside (SNP) were determined before and 20 min after treatment with CHX (0.3–1 mg/kg iv) using a closed cranial window and intravital microscopy. We also determined baseline and arachidonic acid (AA)-stimulated cortical PGF2αand 6-keto-PGF1αproduction before and 20–60 min after CHX (1 mg/kg iv) treatment, using ELISA kits. CHX did not affect baseline diameters (∼100 μm) but significantly decreased arteriolar dilation to COX-dependent stimuli, such as hypercapnia and hypotension, but not to COX-independent SNP. In the 1 mg/kg CHX-treated group, increases in vascular diameters were reduced from 22 ± 2 to 10 ± 2%, from 49 ± 5 to 31 ± 3% (means ± SE, 5 and 10% CO2, respectively, n = 8), from 12 ± 3 to 3 ± 1%, and from 26 ± 5 to 6 ± 2% (∼25 and 40% decreases in blood pressure, respectively, n = 6). CHX also inhibited conversion of exogenous AA to both PGF2αand 6-keto-PGF1α; for example, 20 min after CHX treatment 10 μg/ml AA-stimulated PGF2αconcentrations in the artificial cerebrospinal fluid decreased from 14.28 ± 3.04 to 5.90 ± 1.26 ng/ml ( n = 9). Thus CHX rapidly decreases COX activity in the piglet cerebral cortex. This result may explain in part the preservation of neuronal function of CHX in cerebral ischemia.
Regional assessment of wall curvature and wall stress in left ventricle with magnetic resonance imaging
Authors: Balzer Philippe , Furber Alain , Delépine Stéphane , Rouleau Frédéric , Lethimonnier Franck , Morel Olivier , Tadéi André , Jallet Pierre , Geslin Philippe , le Jeune Jean-Jacques
Published: December 2017

Left ventricular functional abnormalities are associated with regional increases of wall stress and modifications of wall curvature. This study describes the integration of the short-axis and long-axis wall curvatures for determining peak systolic wall stress. Quantification was realized with cine magnetic resonance imaging (MRI) from the location of the endocardial and epicardial borders of the left ventricle on pairs of consecutive short-axis sections. Fifteen normal volunteers were subjected to cine MRI, and different methods of calculating peak systolic wall stress were compared. A short-axis analysis showed a 55 ± 13% increase of the circumferential mean of the peak systolic wall stress between apical and basal sections. Regarding the curvature, no significant increase of wall stress was observed except on the septal wall (31 ± 18%). Short-axis studies proved to be insufficient for determining the regional variations of left ventricular wall stress and for providing normal reference values for the location of abnormal regions in patients.
Echocardiographic determination of risk area size in a murine model of myocardial ischemia
Authors: Scherrer-Crosbie M. , Steudel W. , Ullrich R. , Hunziker P. R. , Liel-Cohen N. , Newell J. , Zaroff J. , Zapol W. M. , Picard M. H.
Published: December 2017

Genetically altered mice are useful to understand cardiac physiology. Myocardial contrast echocardiography (MCE) assesses myocardial perfusion in humans. We hypothesized it could evaluate murine myocardial perfusion before and after acute coronary ligation. MCE was performed before and after this experimental myocardial infarction (MI) in anesthetized mice by intravenous injection of contrast microbubbles and transthoracic echo imaging. Time-video intensity curves were obtained for the anterior, lateral, and septal myocardial walls. After MI, MCE defects were compared with the area of no perfusion measured by Evans blue staining. In healthy animals, intramyocardial contrast was visualized in all the cardiac walls. The anterior wall had a higher baseline video intensity (53 ± 17 arbitrary units) than the lateral (34 ± 13) and septal (27 ± 13) walls ( P < 0.001) and a lower increase in video intensity after contrast injection [50 ± 17 vs. 60 ± 24 (lateral) and 65 ± 29 (septum), P < 0.01]. After MI, left ventricular (LV) dimensions were enlarged, and the shortening fraction was decreased. A perfusion defect was imaged with MCE in every mouse, with a correlation between MCE perfusion defect size (35 ± 13%) and the nonperfused area by Evans blue (37 ± 16%, y = 0.77 x + 6.1, r = 0.93, P < 0.001). Transthoracic MCE is feasible in the mouse and can accurately detect coronary occlusions and quantitate nonperfused myocardium.
Molecular and functional distributions of chloride conductances in rabbit ventricle
Authors: Wong Kevin R. , Trezise Ann E. O. , Bryant Simon , Hart George , Vandenberg Jamie I.
Published: December 2017

The regulation of cardiac electrical activity is critically dependent on the distribution of ion channels in the heart. For most ion channels, however, the patterns of distribution and what regulates these patterns are not well characterized. The most likely candidates for the genes that encode the cAMP- and swelling-activated chloride conductances in the heart are an alternatively spliced variant of CFTR and ClC-3, respectively. In this study we have 1) measured the density of CFTR and ClC-3 mRNA levels across the left ventricular free wall (LVFW) of the rabbit heart using in situ hybridization and 2) measured the corresponding current density of cAMP- and swelling-activated chloride channels in myocytes isolated from subepicardial, midmyocardial, and subendocardial regions of the LVFW. There was a highly significant gradient in the whole cell slope conductance of cAMP-activated chloride currents; normalized slope conductance at 0 mV was 15.7 ± 1.8 pS/pF ( n = 9) in subepicardial myocytes, 7.8 ± 1.5 pS/pF ( n = 11) in midmyocardial myocytes, and 4.9 ± 1.1 pS/pF ( n = 9) in subendocardial myocytes. The level of CFTR mRNA was closely correlated with the density of cAMP-activated chloride conductances in different regions of the heart, with the level of CFTR mRNA being three times higher in the subepicardium than in the subendocardium. The whole cell slope conductance of swelling-activated chloride channel activity, measured 3–5 min after the commencement of cell swelling, was higher in myocytes isolated from the subepicardium than in myocytes isolated from the midmyocardium or subendocardium. In contrast, there was a uniform expression of ClC-3 mRNA across the LVFW of the rabbit heart. These results suggest that the control of gene expression is an important contributor in regulating the distribution of cAMP-activated chloride channels in the rabbit heart but that it may be less important for the swelling-activated chloride channels.
Involvement of ATP-sensitive K+ channels in spontaneous activity of isolated lymph microvessels in rats
Authors: Mizuno Risuke , Ono Nobuyuki , Ohhashi Toshio
Published: December 2017

Physiological roles of ATP-sensitive K+ channels for spontaneous activity in isolated rat mesenteric lymph microvessels (maximum diameter ∼80–150 μm) were investigated. The lymph microvessels were cannulated with glass micropipettes and pressurized at a perfusion pressure of 6 cmH2O. Changes in the diameter and frequency of spontaneous contractions in the lymphatics were measured with videomicroscopy. Pinacidil (K+-channel opener) inhibited the spontaneous activity. In the presence of glibenclamide (selective ATP-sensitive K+-channel blocker; 10−7 and 10−6 M) and tetraethylammonium (TEA; nonselective K+-channel blocker; 10−4 and 10−3 M), the pinacidil-induced inhibition of the spontaneous contractions in lymph microvessels was significantly reversed. Glibenclamide and TEA themselves, however, did not affect the frequency of spontaneous activity in the lymph microvessels. These results suggest that ATP-sensitive K+ channels are involved in the regulation of spontaneous activity in the smooth muscles of isolated lymph microvessels of rat mesenteries.
Endothelin A receptor is necessary for O2constriction but not closure of ductus arteriosus
Authors: Coceani F. , Liu Y.-A. , Seidlitz E. , Kelsey L. , Kuwaki T. , Ackerley C. , Yanagisawa M.
Published: December 2017

In vitro and in vivo techniques were developed with genetically modified mice to determine whether endothelin-1 (ET-1) functions as an O2mediator in closure of the ductus arteriosus (DA) at birth. Wild-type CD-1 and 129/SvEv mice with ETAreceptor −/−, +/−, and +/+ genotypes were used. Isolated DA from term ETA+/+ fetuses contracted to O2(5–95%) and a thromboxane A2analog (ONO-11113, 0.1 μM). Instead, ET-1 elicited a dual response with weak relaxation (0.1 nM) preceding contraction (1–100 nM). Indomethacin (2.8 μM) was also a constrictor. ETA−/− DA, unlike ETA+/+ DA, contracted marginally to O2and ET-1 but responded to ONO-11113. O2contraction was also reduced in ETA+/− DA. In vivo, DA constricted equally in tracheotomized ETA−/− and ETA+/+ newborns. Conversely, no DA constriction was seen in hyperoxic ETA−/− fetuses in utero, although it occurred in ETA+/+ and +/− littermates. We conclude that ET-1 mediates the DA constrictor response to O2. Without ET-1, however, the vessel still closes postnatally, conceivably caused by the withdrawal of relaxing influence(s).
Regional ischemia in hypertrophic Langendorff-perfused rat hearts
Authors: Ashruf J. F. , Ince C. , Bruining H. A.
Published: December 2017

Myocardial hypertrophy decreases the muscle mass-to-vascularization ratio, thereby changing myocardial perfusion. The effect of these changes on myocardial oxygenation in hypertrophic Langendorff-perfused rat hearts was measured using epimyocardial NADH videofluorimetry, whereby ischemic myocardium displays a high fluorescence intensity. Hypertrophic hearts, in contrast to control hearts, developed ischemic areas during oxygen-saturated Langendorff perfusion. Reoxygenation of control hearts after a hypoxic episode resulted in a swift decrease of fluorescence in a heterogeneous pattern of small, evenly dispersed, highly fluorescent patches. Identical patterns could be evoked by occluding capillaries with microspheres 5.9 μm in diameter. Ten seconds after reoxygenation there were no more dysoxic areas, whereas reoxygenation in hypertrophic hearts showed larger ischemic areas that took significantly longer to return to normoxic fluorescence intensities. Hypothesizing that the larger areas originate at a vascular level proximal to the capillary network, we induced hypoxic patterns by embolizing control hearts with microspheres 9.8 and 15 μm in diameter. The frequency distribution histograms of these dysoxic surface areas matched those of hypertrophic hearts and differed significantly from those of hearts embolized with 5.9-μm microspheres. These results suggest the existence of areas in hypertrophic Langendorff-perfused hearts with suboptimal vascularization originating at the arteriolar and/or arterial level.
ACE inhibition improves cardiac NE uptake and attenuates sympathetic nerve terminal abnormalities in heart failure
Authors: Kawai Hiroya , Fan Tai-Hwang M. , Dong Erdan , Siddiqui Rizwan A. , Yatani Akito , Stevens Suzanne Y. , Liang Chang-Seng
Published: December 2017

Cardiac sympathetic nerve terminal dysfunction plays an important role in the downregulation of myocardial β-adrenoceptors in heart failure. To determine whether chronic angiotensin-converting enzyme (ACE) inhibition improved cardiac sympathetic nerve terminal function and hence increased myocardial β-adrenergic responsiveness, we administered ACE inhibitors to dogs with chronic right-sided heart failure (RHF) produced by tricuspid avulsion and pulmonary artery constriction. The RHF animals exhibited fluid retention, elevated right heart filling pressures, blunted inotropic response to isoproterenol, and reduced β-adrenoceptor density. These changes were accompanied by decreases in right ventricular norepinephrine (NE) uptake and neuronal NE histofluorescence and tyrosine hydroxylase immunoreactive profiles. ACE inhibitors had no effect on the production of heart failure but greatly reduced the attenuation of cardiac NE uptake, neuronal NE histofluorescence, and tyrosine hydroxylase immunoreactive profiles. ACE inhibition also improved the inotropic response to isoproterenol and restored myocardial β-adrenoceptor density. The changes probably are caused by reduction of cardiac NE release by ACE inhibition and may contribute to the beneficial effects of ACE inhibitor therapy in patients with chronic heart failure.
A13C NMR double-labeling method to quantitate local myocardial O2consumption using frozen tissue samples
Authors: van Beek Johannes H. G. M. , van Mil Harald G. J. , King Richard B. , de Kanter Frans J. J. , Alders David J. C. , Bussemaker Joli
Published: December 2017

Measurement of local myocardial O2consumption (V˙o2) has been problematic but is needed to investigate the heterogeneity of aerobic metabolism. The goal of the present investigation was to develop a method to measure local V˙o2using small frozen myocardial samples, suitable for determiningV˙o2profiles. In 26 isolated rabbit hearts, 1.5 mmol/l [2-13C]acetate was infused for 4 min, followed by 1.5 min of [1,2-13C]acetate. The left ventricular (LV) free wall was then quickly frozen. High-resolution13C-NMR spectra were measured from extracts taken from 2- to 3-mm thick transmural layer samples. The multiplet intensities of glutamate were analyzed with a computer model allowing simultaneous estimation of the absolute flux through the tricarboxylic acid cycle and the fractional contribution of acetate to acetyl CoA formation from which localV˙o2was calculated. The13C-derivedV˙o2in the LV free wall was linearly related to “gold standard”V˙o2from coronary venous O2electrode measurements in the same region ( r = 0.932, n = 22, P < 0.0001, slope 1.05) for control and lowered metabolic rates. The ratio of subendocardial to subepicardial V˙o2was 1.52 ± 0.19 (SE, significantly >1, P< 0.025). Local myocardialV˙o2can now be quantitated with this new13C method to determine profiles of aerobic energy metabolism.
Baroreflex stabilization of the double product
Authors: van Vliet Bruce N. , Montani Jean-Pierre
Published: December 2017

We investigated whether the baroreflex control of heart rate (HR) stabilizes the product of arterial pressure (PA) and HR, called the double product (DP), an indirect indicator of left ventricular oxygen consumption. During pharmacological increases and decreases of PA in conscious rabbits, the mean (±SE) rate of change of the DP with respect to PA(dDP/dPA) was −88 ± 36 and −20 ± 36 DP units/mmHg, respectively. Regression analysis of all peak responses obtained in individual rats produced a dDP/dPA value of 15 ± 16 DP units/mmHg. These estimates were significantly less than the dDP/dPA value predicted if HR were constant (184 ± 7 DP units/mmHg) and were not significantly different from zero. We also compared values of baroreflex sensitivity (BRS) from the literature with those calculated to provide ideal stabilization of the DP. BRS values were significantly correlated with the calculated ideal values ( R = 0.95; n = 14). BRS averaged 128 ± 24% of the ideal value in all species and 148 ± 28% in mammals and birds. Our results suggest that stabilization of the DP is a common consequence of the baroreflex control of heart rate.
Relation between outer and luminal diameter in cannulated arteries
Authors: Faury Gilles , Maher Gail M. , Li Dean Y. , Keating Mark T. , Mecham Robert P. , Boyle Walter A.
Published: December 2017

Resistance in blood vessels is directly related to the inner (luminal) diameter (ID). However, ID can be difficult to measure during physiological experiments because of poor transillumination of thick-walled or tightly constricted vessels. We investigated whether the wall cross-sectional area (WCSA) in cannulated arteries is nearly constant, allowing IDs to be calculated from outer diameters (OD) using a single determination of WCSA. With the use of image analysis, OD and ID were directly measured using either transillumination or a fluorescent marker in the lumen. IDs from a variety of vessel types were calculated from WCSA at several reference pressures. Calculated IDs at all of the reference WCSA were within 5% (mean <1%) of the corresponding measured IDs in all vessel types studied, including vessels from heterozygote elastin knockout animals. This was true over a wide range of transmural pressures, during treatment with agonists, and before and after treatment with KCN. In conclusion, WCSA remains virtually constant in cannulated vessels, allowing accurate determination of ID from OD measurement under a variety of experimental conditions.
Smaller infarct after preconditioning does not predict extent of early functional improvement of reperfused heart
Authors: Cohen Michael V. , Yang Xi-Ming , Downey James M.
Published: December 2017

We evaluated the ability of ischemic preconditioning to restore function to salvaged myocardium in rabbits. Although ischemic preconditioning reduces infarct size, few investigators studying recovery of function after coronary occlusions lasting ≥30 min have reported any mechanical benefit in preconditioned hearts. However, because myocardial function was seldom evaluated beyond 5 h after reperfusion stunning may have masked the benefit. Accordingly, rabbits were chronically instrumented with a pneumatic occluder around a branch of the left coronary artery, a pair of 1-mm ultrasonic crystals in the myocardial territory destined to become ischemic, and electrocardiogram (ECG) leads. One week after surgery the ECG and segment length tracing were recorded at rest, during 30-min occlusion and 1 h of reflow, and again at 24, 48, and 72 h. In ischemically preconditioned rabbits, 5-min coronary occlusion and 10-min reperfusion preceded the long occlusion. The beginning and end of systole were determined by recording the first and second heart sounds with a hand-held precordial microphone. Postmortem infarct size was measured with triphenyltetrazolium chloride. During the 30-min coronary occlusion all segments became nearly akinetic or bulged during systole. After 60 min of reflow there was little return of function in either group. Between 24 and 72 h there was minimal recovery in the control group (segment shortening equals 13.3 ± 4.1% of baseline), whereas function was much better in preconditioned hearts (44.2 ± 7.4% of baseline, P < 0.02). Infarct size as a percentage of risk zone was much smaller in preconditioned hearts (10.2 ± 1.4 vs. 29.7 ± 1.8%, P < 0.001). Thus there is a gradual recovery of systolic function of reperfused myocardium after a coronary occlusion. Although early mechanical recovery is significantly better after preconditioning, it is much less than would be predicted by the reduction of infarct size.
5-HT4 receptors in nucleus tractus solitarii attenuate cardiopulmonary reflex in anesthetized rats
Authors: Edwards Emma , Paton Julian F. R.
Published: December 2017

We determined whether the cAMP-protein kinase A (PKA) pathway modulation of the cardiopulmonary reflex was caused by activation of 5-HT4 receptors at the level of the nucleus tractus solitarii (NTS) of the anesthetized rat. NTS microinjection of 5-methoxytryptamine (5-MeOT, 2.25 pmol, n = 13), a 5-HT-receptor agonist, attenuated the cardiopulmonary reflex-evoked bradycardia and tachypnea. Microinjection of RS-39604 (4.5 pmol, n = 6), a selective 5-HT4-receptor antagonist, blocked the attenuating effect of 5-MeOT. NTS microinjection of 8-bromoadenosine 3′,5′-cyclic monophosphate (8-BrcAMP, 9 nmol, 45 nl, n = 10), a membrane-permeant analog of cAMP, significantly attenuated the reflex bradycardia and tachypnea. Rp-adenosine 3′,5′-cyclic monophosphorothioate (4.5 nmol, n = 6), a cAMP-dependent PKA inhibitor, had no effect on the cardiopulmonary reflex when microinjected into the NTS alone but when given before a microinjection of either 8-BrcAMP ( n = 6) or 5-MeOT ( n = 6) blocked the attenuating effect on the reflex-evoked bradycardia. Thus stimulation of 5-HT4 receptors within the NTS depresses the reflex bradycardia components of the cardiopulmonary reflex via a cAMP-dependent PKA pathway.
Weibull distribution function for cardiac contraction: integrative analysis
Authors: Araki Junichi , Matsubara Hiromi , Shimizu Juichiro , Mikane Takeshi , Mohri Satoshi , Mizuno Ju , Takaki Miyako , Ohe Tohru , Hirakawa Masahisa , Suga Hiroyuki
Published: December 2017

The Weibull distribution is widely used to analyze the cumulative loss of performance, i.e., breakdown, of a complex system in systems engineering. We found for the first time that the difference curve of two Weibull distribution functions almost identically fitted the isovolumically contracting left ventricular (LV) pressure-time curve [P( t)] in all 345 beats (3 beats at each of 5 volumes in 23 canine hearts; r = 0.999953 ± 0.000027; mean ± SD). The first derivative of the difference curve also closely fitted the first derivative of the P( t) curve. These results suggest the possibility that the LV isovolumic P( t) curve may be characterized by two counteracting cumulative breakdown systems. Of these, the first breakdown system causes a gradual pressure rise and the second breakdown system causes a gradual pressure fall. This Weibull-function model of the heart seems to give a new systems engineering or integrative physiological view of the logic underlying LV isovolumic pressure generation.
Sequential gating in the human heart K+ channel Kv1.5 incorporatesQ 1 andQ 2 charge components
Authors: Hesketh J. Christian , Fedida David
Published: December 2017

On-gating current from the Kv1.5 cardiac delayed rectifier K+ channel expressed in HEK-293 cells was separated into two distinct charge systems, Q 1 and Q 2, obtained from double Boltzmann fits to the charge-voltage relationship. Q 1 and Q 2 had characteristic voltage dependence and sensitivity with half-activation potentials of −29.6 ± 1.6 and −2.19 ± 2.09 mV and effective valences of 1.87 ± 0.15 and 5.53 ± 0.27 e −, respectively. The contribution to total gating charge was 0.20 ± 0.04 for Q 1 and 0.80 ± 0.04 ( n = 5) for Q 2. At intermediate depolarizations, heteromorphic gating current waveforms resulted from relatively equal contributions from Q 1 and Q 2, but with widely different kinetics. Prepulses to −20 mV moved only Q 1, simplified on-gating currents, and allowed rapid Q 2 movement. Voltage-dependent on-gating current recovery in the presence of 4-aminopyridine (1 mM) suggested a sequentially coupled movement of the two charge systems during channel activation. This allowed the construction of a linear five-state model of Q 1 and Q 2 gating charge movement, which predicted experimental on-gating currents over a wide potential range. Such models are useful in determining state-dependent mechanisms of open and closed channel block of cardiac K+ channels.
Effects of ACE inhibition and β-receptor blockade on energy metabolism in rats postmyocardial infarction
Authors: Hügel Stephanie , Horn Michael , de Groot Mark , Remkes Helga , Dienesch Charlotte , Hu Kai , Ertl Georg , Neubauer Stefan
Published: December 2017

Chronic treatment with β-receptor blockers or angiotensin-converting enzyme (ACE) inhibitors in heart failure can reduce mortality and improve left ventricular function, but the mechanisms involved in their beneficial action remain to be fully defined. Our hypothesis was that these agents prevent the derangement of cardiac energy metabolism. Rats were subjected to myocardial infarction (MI) or sham operation. Thereafter, animals were treated with bisoprolol, captopril, or remained untreated. Two months later, cardiac function was measured in the isolated heart by a left ventricular balloon (pressure-volume curves), and energy metabolism of residual intact myocardium was analyzed in terms of total and isoenzyme creatine kinase (CK) activity, steady-state levels (ATP, phosphocreatine), and turnover rates (CK reaction velocity) of high-energy phosphates (31P nuclear magnetic resonance) and total creatine content (HPLC). Bisoprolol and partially captopril prevented post-MI hypertrophy and partially prevented left ventricular contractile dysfunction. Residual intact failing myocardium in untreated, infarcted hearts showed a 25% decrease of the total, a 26% decrease of MM-, and a 37% decrease of the mitochondrial CK activity. Total creatine was reduced by 15%, phosphocreatine by 21%, and CK reaction velocity by 41%. Treatment with bisoprolol or captopril largely prevented all of these changes in infarcted hearts. Thus the favorable functional effects of β-receptor blockers and ACE inhibitors post-MI are accompanied by substantial beneficial effects on cardiac energy metabolism.
Alterations in contractile properties and Ca2+ handling in streptozotocin-induced diabetic rat myocardium
Authors: Ishikawa Tetsuya , Kajiwara Hidetoshi , Kurihara Satoshi
Published: December 2017

The mechanisms of the slower time courses of Ca2+transients (CaT) and contraction in diabetic (diabetes mellitus, DM) myocardium were studied. The aequorin method was applied to papillary muscles of streptozotocin-induced DM and control rats. The time courses of CaT and tension of twitch in DM were slower than those in control, although the magnitudes of the CaT and contraction were identical. The dependence of CaT decay time and relaxation time on developed tension in DM and control rats differed. The length-tension relation in twitch and the pCa-tension relation in tetanus were identical in the two groups. The magnitude of extra Ca2+ (transient increase in intracellular Ca2+ concentration induced by a quick release in tetanus) was identical in both groups. pCa-tension relations of skinned trabeculae at different sarcomere lengths were nearly identical. The cross-bridge cycling rate (CCR) in DM was slower than that in control. These results indicate that the tension-dependent change in the Ca2+ affinity of troponin C in DM myocardium functions as in control myocardium. The slower time courses of CaT and tension in DM myocardium are caused by slower Ca2+ uptake by the sarcoplasmic reticulum and the slower CCR.
Effects of modest anemia on systemic and coronary circulation of septic sheep
Authors: Bloos Frank , Martin Claudio M. , Ellis Chris G. , Sibbald William J.
Published: December 2017

Although a lower transfusion trigger is generally recommended, little evidence is available about the physiological mechanisms of mild anemia in diseases with an imbalance between O2supply and O2 demand such as sepsis. This study was undertaken to describe the systemic and coronary metabolic O2 reserve in an awake sheep model of hyperdynamic sepsis comparing two different hemoglobin levels. Twenty-four hours after sheep were rendered septic by cecal ligation and perforation (CLP), blood transfusion ( n = 7, hemoglobin = 120 g/l) and isovolemic hemodilution ( n = 8, hemoglobin = 70 g/l), respectively, were performed. Another 24 h later, we measured hemodynamics, organ blood flows, and systemic and myocardial O2 metabolism variables at baseline and through four stages of progressive hypoxia. Maximum coronary blood flow was 766.3 ± 87.4 ml ⋅ min−1 ⋅ 100 g−1 in hemodiluted sheep group versus 422.7 ± 53.7 ml ⋅ min−1 ⋅ 100 g−1 in the transfused sheep ( P < 0.01). Myocardial O2 extraction was higher in the transfusion group ( P = 0.03) throughout the whole hypoxia trial. In the hemodilution group, coronary blood flow increased more per increase in myocardial O2 uptake than in transfused sheep ( P < 0.01). This was accompanied by a lower left ventricular epicardial-to-endocardial flow ratio in hemodiluted sheep (1.13 ± 0.07) than in transfused sheep (1.34 ± 0.02, P < 0.05). We conclude that the lower coronary blood flow and greater myocardial O2 extraction in transfused septic sheep preserves transmyocardial O2metabolism better in comparison to hemodiluted sheep.
Generation of superoxide in cardiomyocytes during ischemia before reperfusion
Authors: Becker Lance B. , vanden Hoek Terry L. , Shao Zuo-Hui , Li Chang-Qing , Schumacker Paul T.
Published: December 2017

Although a burst of oxidants has been well described with reperfusion, less is known about the oxidants generated by the highly reduced redox state and low O2of ischemia. This study aimed to further identify the species and source of these oxidants. Cardiomyocytes were exposed to 1 h of simulated ischemia while oxidant generation was assessed by intracellular dihydroethidine (DHE) oxidation. Ischemia increased DHE oxidation significantly (0.7 ± 0.1 to 2.3 ± 0.3) after 1 h. Myxothiazol (mitochondrial site III inhibitor) attenuated oxidation to 1.3 ± 0.1, as did the site I inhibitors rotenone (1.0 ± 0.1), amytal (1.1 ± 0.1), and the flavoprotein oxidase inhibitor diphenyleneiodonium (0.9 ± 0.1). By contrast, the site IV inhibitor cyanide, as well as inhibitors of xanthine oxidase (allopurinol), nitric oxide synthase (nitro-l-arginine methyl ester), and NADPH oxidase (apocynin), had no effect. Finally, DHE oxidation increased with Cu- and Zn-containing superoxide dismutase (SOD) inhibition using diethyldithiocarbamate (2.7 ± 0.1) and decreased with exogenous SOD (1.1 ± 0.1). We conclude that significant superoxide generation occurs during ischemia before reperfusion from the ubisemiquinone site of the mitochondrial electron transport chain.
Human VEGF gene expression in skeletal muscle: effect of acute normoxic and hypoxic exercise
Authors: Richardson R. S. , Wagner H. , Mudaliar S. R. D. , Henry R. , Noyszewski E. A. , Wagner P. D.
Published: December 2017

Vascular endothelial growth factor (VEGF) is involved in extracellular matrix changes and endothelial cell proliferation, both of which are precursors to new capillary growth. Angiogenesis is a vital adaptation to exercise training, and the exercise-induced reduction in intracellular[Formula: see text] has been proposed as a stimulus for this process. Thus we studied muscle cell[Formula: see text] [myoglobin[Formula: see text]([Formula: see text])] during exercise in normoxia and in hypoxia (12% O2) and studied the mRNA levels of VEGF in six untrained subjects after a single bout of exercise by quantitative Northern analysis. Single-leg knee extension provided the acute exercise stimulus: a maximal test followed by 30 min at 50% of the peak work rate achieved in this graded test. Because peak work rate was not affected by hypoxia, the absolute and relative work rates were identical in hypoxia and normoxia. Three pericutaneous needle biopsies were collected from the vastus lateralis muscle, one at rest and then the others at 1 h after exercise in normoxia or hypoxia. At rest (control), VEGF mRNA levels were very low (0.38 ± 0.04 VEGF/18S). After exercise in normoxia or hypoxia, VEGF mRNA levels were much greater (16.9 ± 6.7 or 7.1 ± 1.8 VEGF/18S, respectively). In contrast, there was no measurable basic fibroblast growth factor mRNA response to exercise at this 1-h postexercise time point. Magnetic resonance spectroscopy of myoglobin confirmed a reduction in[Formula: see text] in hypoxia (3.8 ± 0.3 mmHg) compared with normoxia (7.2 ± 0.6 mmHg) but failed to reveal a relationship between [Formula: see text] during exercise and VEGF expression. This VEGF mRNA increase in response to acute exercise supports the concept that VEGF is involved in exercise-induced skeletal muscle angiogenesis but questions the importance of a reduced cellular [Formula: see text]as a stimulus for this response.
Contribution of carotid chemoreceptors to mesenteric venoconstriction during acute hypercapnia in rabbits
Authors: Tominaga Masamune , Stekiel Thomas A. , Bosnjak Zeljko J. , Kampine John P.
Published: December 2017

The contribution of carotid chemoreceptors to hypercapnia-induced mesenteric venoconstriction was examined in 12 α-chloralose-anesthetized rabbits (1.0–1.6 kg). Surgical preparation consisted of a tracheotomy, femoral arterial and venous cannulation, and a midline laparotomy through which a 13-cm loop of ileum was exteriorized and superfused with physiological salt solution. Mesenteric vein diameter and intravenous pressure (using a servo-null measurement system) were measured in 500- to 1,000-μm mesenteric veins during 40-s periods of 15%, 20%, and 25% CO2 inhalation. Measurements were then repeated following bilateral ablation of the carotid chemoreceptors. Before denervation, mesenteric vein diameter constricted 6.5 ± 1.1%, 11.9 ± 1.1%, and 17.9 ± 2.2% during the 15%, 20%, and 25% CO2 inhalation, respectively. After denervation, these values were reduced to 5.0 ± 0.9%, 6.9 ± 1.2%, and 8.4 ± 1.3%, respectively. We conclude that activation of the carotid chemoreceptors by hypercapnia induces active mesenteric venoconstriction. After denervation of the carotid baroreceptors and chemoreceptors, there was also a small decrease in venule diameter proportional to the level of inspired CO2. We further conclude that noncarotid body chemoreceptor activation contributes to mesenteric venular constriction.
Factors governing mechanical stimulation in frog hearts
Authors: Fasciano Robert W. , Tung Leslie
Published: December 2017

Because stretch-induced activation may be important in generating clinically relevant arrhythmias in the heart, we delineated the ability of different types of stretches to activate ventricular tissue. Geometrically simple sheets of frog ( Rana catesbeiana) ventricular tissue were mounted to allow stretches to be applied perpendicular to one edge. Every heart could be activated by a stretch pulse ( n = 25), and several parameters were varied to determine their effects on mechanical activation threshold. At shorter coupling intervals, a larger stretch was needed to excite the tissue, and activation-recovery intervals were shorter, similar to previously published electrically probed strength-interval and restitution relations. Additionally, the tissue became easier to activate as the speed of the stretch increased from 0.09 to 2.6% length/ms. The increment in stretch needed for activation decreased as the baseline stretch increased from 0 to 6% length. Thus we show that mechanical activation is similar to electrical activation and that increasing uniquely mechanical parameters such as the speed of the applied stretch or baseline level of stretch can decrease the mechanical activation threshold.
Functional, biochemical, and molecular investigations of renal kallikrein-kinin system in diabetic rats
Authors: Tschöpe C. , Reinecke A. , Seidl U. , Yu M. , Gavriluk V. , Riester U. , Gohlke P. , Graf K. , Bader M. , Hilgenfeldt U. , Pesquero J. B. , Ritz E. , Unger T.
Published: December 2017

A reduction of renal kallikrein has been found in non-insulin-treated diabetic individuals, suggesting that an impaired renal kallikrein-kinin system (KKS) contributes to the development of diabetic nephropathy. We analyzed relevant components of the renal KKS in non-insulin-treated streptozotocin (STZ)-induced diabetic rats. Twelve weeks after a single injection of STZ, rats were normotensive and displayed hyperglycemia, polyuria, proteinuria, and reduced glomerular filtration rate. Blood bradykinin (BK) levels and prekallikrein activity were significantly increased compared with controls. Renal kallikrein activity was reduced by 70%, whereas urinary BK levels were increased up to threefold. Renal kininases were decreased as indicated by a 3-fold reduction in renal angiotensin-converting enzyme activity and a 1.8-fold reduction in renal expression of neutral endopeptidase 24.11. Renal cortical expression of kininogen and B2receptors was enhanced to 1.4 and 1.8-fold, respectively. Our data suggest that increased urinary BK levels found in severely hyperglycemic STZ-diabetic rats are related to increased filtration of components of the plasma KKS and/or renal kininogen synthesis in combination with decreased renal kinin-degrading activity. Thus, despite reduced renal kallikrein synthesis, renal KKS is activated in the advanced stage of diabetic nephropathy.
Role of capillaries in determining CBF reserve: new insights using myocardial contrast echocardiography
Authors: Jayaweera Ananda R. , Wei Kevin , Coggins Matthew , Bin Jiang Ping , Goodman Craig , Kaul Sanjiv
Published: December 2017

To define the role of capillaries in the control of coronary blood flow (CBF) reserve, we developed a model of the coronary circulation and evaluated experimental data in its context. Our model comprised three compartments connected in series (arterial, capillary, and venous), each with its own resistance. The resistance in each vascular compartment was derived from the model based on hemodynamic data obtained in nine dogs during baseline and stenosis, both at rest and during hyperemia. The capillary hydrostatic pressure was assumed to be constant in all stages. Although in the absence of stenosis, the contribution of capillaries to total myocardial vascular resistance was only 25 ± 5% at rest, it increased to 75 ± 14% during hyperemia, despite the total myocardial vascular resistance decreasing by 51 ± 13%. In the presence of a noncritical stenosis, total myocardial vascular resistance decreased by 22 ± 10% at rest, with no change in capillary resistance. During hyperemia, total myocardial vascular resistance increased by 58 ± 50% in the presence of the noncritical stenosis. In this situation, because arteriolar and venular resistances were already minimal, the increase in myocardial vascular resistance was due to increased capillary resistance, making it the predominant source (84 ± 8%) of total myocardial vascular resistance. Myocardial video intensity (VI) on myocardial contrast echocardiography (MCE), which reflects capillary blood volume, decreased distal to the stenosis during hyperemia. In the presence of a flow-limiting stenosis at rest, myocardial VI also decreased, indicating that decrease in CBF was associated with an increase in capillary resistance. Our findings also provide an alternative explanation for the critical coronary closing pressure. Thus, contrary to previously held notions, capillaries play a vital role in the regulation of CBF.
Glycolipid RC-552 induces delayed preconditioning-like effect via iNOS-dependent pathway in mice
Authors: Xi Lei , Salloum Fadi , Tekin Demet , Jarrett Novlet C. , Kukreja Rakesh C.
Published: December 2017

We recently demonstrated that monophosphoryl lipid A (MLA)-induced delayed cardioprotection is mediated by inducible nitric oxide synthase (iNOS) in mice. In the present study, we determined whether RC-552, a novel synthetic glycolipid related in chemical structure to MLA, could afford similar protection. Adult mice were pretreated with vehicle or RC-552 (350 μg/kg ip, n = 7 mice/group) 24 h before global ischemia and reperfusion in a Langendorff isolated, perfused heart model. A group of RC-552-treated mice received S-methylisothiourea (SMT), a selective inhibitor of iNOS (3 mg/kg ip), 30 min before heart perfusion. Myocardial infarct size was significantly reduced from 19.2 ± 2.0% in vehicle to 8.2 ± 2.9% in RC-552 group ( P < 0.05). Treatment with SMT abolished RC-552-induced reduction in infarct size (20.0 ± 3.9%). In addition, RC-552 failed to reduce infarct size in isolated hearts from iNOS knockout mice (27.1 ± 2.8%) compared with that in hearts from control knockout mice without drug treatment (22.9 ± 5.4%). Acute buffer perfusion with RC-552 (0.1, 1.0, or 2.5 μg/ml) for 8 min immediately before ischemia-reperfusion did not reduce infarct size significantly. We concluded that RC-552 induces delayed cardioprotection via an iNOS-dependent pathway.
AT1-receptor blockade enhances ischemic preconditioning in hypertrophied rat myocardium
Authors: Butler Karyn L. , Huang Alice H. , Gwathmey Judith K.
Published: December 2017

The purpose of this study was to determine whether ischemic preconditioning protects contractile function in hypertrophied rat myocardium from ischemia-reperfusion (I/R) injury. Male salt-sensitive rats were fed a high-salt diet for 2 wk to induce myocardial hypertrophy. Nonhypertrophied hearts were obtained from age-matched Sprague-Dawley (SD) rats fed a regular diet. Heart weight-to-body weight ratios were higher in salt-sensitive rats than in SD rats (6.9 ± 0.2 vs. 4.7 ± 0.2 g/kg, P < 0.01). A second group of salt-sensitive and SD rats was administered losartan (10 mg ⋅ kg−1 ⋅ day−1), an AT1-receptor blocker, for 1 wk before the study. Isolated hearts were preconditioned with transient ischemia before global I/R. After I/R, preconditioned hypertrophied hearts exhibited greater recovery of left ventricular developed pressure compared with that of preconditioned normal hearts (73 ± 8 vs. 18 ± 8%, P < 0.01). Left ventricular developed pressure was further enhanced by losartan in both hypertrophied and normal myocardium (99 ± 5 vs. 73 ± 8%, P < 0.05 and 97 ± 15 vs. 18 ± 8%, P < 0.01). Hypertrophied rat myocardium can be protected from I/R-induced contractile dysfunction by ischemic preconditioning. Losartan improves the ischemic tolerance of normal and hypertrophied myocardium.
Differential effects of pressure or volume overload on myocardial MMP levels and inhibitory control
Authors: Nagatomo Yoshitatsu , Carabello Blase A. , Coker Mytsi L. , McDermott Paul J. , Nemoto Shintaro , Hamawaki Masayoshi , Spinale Francis G.
Published: December 2017

Left ventricular (LV) pressure (PO) or volume (VO) overload is accompanied by myocardial remodeling, but mechanisms that contribute to this progressive remodeling process remain unclear. The matrix metalloproteinases (MMPs) contribute to tissue remodeling in a number of disease states. This study tested the hypothesis that increased MMP expression and activity occur after the induction of an LV overload, which is accompanied by a loss of endogenous MMP inhibitory control. LV MMP zymographic activity and species abundance were measured in dogs under the following conditions: acute PO induced by ascending aortic balloon inflation (6 h, n = 9), prolonged PO by aortic banding (10 days, n = 5), acute VO through mitral regurgitation secondary to chordal rupture (6 h, n = 6), prolonged VO due to mitral regurgitation (14 days, n = 7), and sham controls ( n = 11). MMP zymographic activity in the 92-kDa region, indicative of MMP-9 activity, increased over threefold in acute PO and VO and fell to control levels in prolonged PO and VO. The MMP-9 activity-to-abundance ratio increased by over fourfold with acute VO and twofold in acute PO, suggesting a loss of inhibitory control. Endogenous MMP inhibitor content was unchanged with either PO or VO. Interstitial collagenase (MMP-1) content decreased by 50% with acute VO but not with acute PO. Stromelysin (MMP-3) levels increased by 40% with acute VO and increased by 80% with prolonged PO. Although changes in LV myocardial MMP activity and inhibitory control occurred in both acute and prolonged PO and VO states, these changes were not identical. These results suggest that the type of overload stimulus may selectively influence myocardial MMP activity and expression, which in turn would affect the overall LV myocardial remodeling process in LV overload.