bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport of fluid and solutes in the body II. Model validation and implications
Authors: Gyenge C. C. , Bowen B. D. , Reed R. K. , Bert J. L.
Published: December 2017

A mathematical model of short-term whole body fluid, protein, and ion distribution and transport developed earlier [see companion paper: C. C. Gyenge, B. D. Bowen, R. K. Reed, and J. L. Bert. Am. J. Physiol. 277 ( Heart Circ. Physiol. 46): H1215–H1227, 1999] is validated using experimental data available in the literature. The model was tested against data measured for the following three types of experimental infusions: 1) hyperosmolar saline solutions with an osmolarity in the range of 2,000–2,400 mosmol/l, 2) saline solutions with an osmolarity of ∼270 mosmol/l and composition comparable with Ringer solution, and 3) an isosmotic NaCl solution with an osmolarity of ∼300 mosmol/l. Good agreement between the model predictions and the experimental data was obtained with respect to the trends and magnitudes of fluid shifts between the intra- and extracellular compartments, extracellular ion and protein contents, and hematocrit values. The model is also able to yield information about inaccessible or difficult-to-measure system variables such as intracellular ion contents, cellular volumes, and fluid fluxes across the vascular capillary membrane, data that can be used to help interpret the behavior of the system.
Cardiac endothelial transport and metabolism of adenosine and inosine
Authors: Schwartz Lisa M. , Bukowski Thomas R. , Revkin James H. , Bassingthwaighte James B.
Published: December 2017

The influence of transmembrane flux limitations on cellular metabolism of purine nucleosides was assessed in whole organ studies. Transcapillary transport of the purine nucleosides adenosine (Ado) and inosine (Ino) via paracellular diffusion through interendothelial clefts in parallel with carrier-mediated transendothelial fluxes was studied in isolated, Krebs-Henseleit-perfused rabbit and guinea pig hearts. After injection into coronary inflow, multiple-indicator dilution curves were obtained from coronary outflow for 90 s for131I-labeled albumin (intravascular reference tracer), [3H]arabinofuranosyl hypoxanthine (AraH; extracellular reference tracer and nonreactive adenosine analog), and either [14C]Ado or [14C]Ino. Ado or Ino was separated from their degradative products, hypoxanthine, xanthine, and uric acid, in each outflow sample by HPLC and radioisotope counting. Ado and Ino, but not AraH, permeate the luminal membrane of endothelial cells via a saturable transporter with permeability-surface area product PSecland also diffuse passively through interendothelial clefts with the same conductance ( PSg) as AraH. These parallel conductances were estimated via fitting with an axially distributed, multi-pathway, four-region blood-tissue exchange model. PSgfor AraH were ∼4 and 2.5 ml ⋅ g−1⋅ min−1in rabbits and guinea pigs, respectively. In contrast, transplasmalemmal conductances (endothelial PSecl) were ∼0.2 ml ⋅ g−1⋅ min−1for both Ado and Ino in rabbit hearts but ∼2 ml ⋅ g−1⋅ min−1in guinea pig hearts, an order of magnitude different. Purine nucleoside metabolism also differs between guinea pig and rabbit cardiac endothelium. In guinea pig heart, 50% of the tracer Ado bolus was retained, 35% was washed out as Ado, and 15% was lost as effluent metabolites; 25% of Ino was retained, 50% washed out, and 25% was lost as metabolites. In rabbit heart, 45% of Ado was retained and 5% lost as metabolites, and 7% of Ino was retained and 3% lost as metabolites. We conclude that endothelial transport of Ado and Ino is a prime determinant of their metabolic fates: where transport rates are high, metabolic transformation is high.
Summation of dynamic transfer characteristics of left and right carotid sinus baroreflexes in rabbits
Authors: Kawada Toru , Sato Takayuki , Shishido Toshiaki , Inagaki Masashi , Tatewaki Teiji , Yanagiya Yusuke , Sugimachi Masaru , Sunagawa Kenji
Published: December 2017

Although interactions among parallel negative-feedback baroreflex systems have been extensively investigated with respect to their steady-state responses, the dynamic interactions remain unknown. In anesthetized, vagotomized, and aortic-denervated rabbits, we perturbed isolated intracarotid sinus pressure (CSP) unilaterally or bilaterally around the physiological operating pressure according to binary white noise. The neural arc transfer function from CSP to cardiac sympathetic nerve activity (SNA) and the peripheral arc transfer function from SNA to aortic pressure were estimated. The gain values of the neural arc at 0.01 Hz estimated by the left (L) and right (R) CSP perturbations were 0.94 ± 0.31 and 0.96 ± 0.25, respectively. The gain value increased to 2.17 ± 0.97 during the bilateral identical CSP perturbation and was not significantly different from L + R. The phase values of the neural arc did not differ among protocols. No significant differences were observed in the peripheral arc transfer functions among protocols. We conclude that summation of the dynamic transfer characteristics of the bilateral carotid sinus baroreflexes around the physiological operating pressure approximates simple addition.
Sympathetic responses to cardiopulmonary vagal afferent stimulation during development
Authors: Merrill David C. , Segar Jeffrey L. , McWeeny Oliva J. , Robillard Jean E.
Published: December 2017

Previous work in our laboratory has demonstrated impairment of cardiopulmonary reflex control of renal sympathetic nerve activity (RSNA) during the newborn period. The present study was designed to test the hypothesis that this delayed maturation is secondary to incomplete central integration of vagal afferent input. Term fetal (135–140 days; n = 6), newborn (3–7 days of age; n = 8), and young adult (6–8 wk old; n = 8) sheep anesthetized with α-chloralose underwent vagal afferent nerve stimulation. All animals had undergone prior sinoaortic denervation to eliminate influences from the arterial baroreceptors. After determination of optimal stimulation parameters, RSNA responses to gradual increases in stimulation frequency (1.0–16 Hz) were recorded and compared by one-way ANOVA. RSNA decreased progressively with increased frequency of stimulation in all three groups of animals. When comparing the three groups at any given frequency of stimulation, reflex withdrawal of RSNA tended to be more pronounced in newborn lambs ( P< 0.05 for 1 and 4 Hz). Heart rate (HR) was also noted to decrease significantly with vagal afferent stimulation in each of the groups, but no significant differences in the reflex decreases in HR were noted among the three groups of animals. These results demonstrate that central integration of vagal afferent input is intact in fetal and newborn sheep. These results suggest that the delayed maturation of cardiopulmonary reflex-mediated changes in RSNA seen early in development appears to depend on intrinsic alterations in baroreceptor function rather than incomplete central integration.
Regulation of respiration in myocardium in the transient and steady state
Authors: Chung Youngran , Jue Thomas
Published: December 2017

1H/31P NMR has followed the metabolic response to increased work in the glucose- and pyruvate-perfused rat myocardium during a heart cycle and at the steady state. With electrical pacing and dobutamine, the heart O2consumption increases by 56%. The phosphocreatine (PCr) level initially declines, but recovers within 15 min to its control level; the oxymyoglobin (MbO2) saturation decreases by 15%. Because the MbO2signal reflects the intracellular [Formula: see text], the capillary-to-cell O2gradient has increased to match the increased O2need. However, no transient metabolic fluctuation is observed in either PCr or MbO2throughout the entire cardiac cycle in both glucose and pyruvate-/glucose-perfused hearts. No systolic-diastolic variation is detectable under either high workload or hypoxic conditions. The results reveal that neither O2nor ADP is regulating respiration under increased energy demand in the steady or transient state.
β-Blockade improves adjacent regional sympathetic innervation during postinfarction remodeling
Authors: Kramer Christopher M. , Nicol Philip D. , Rogers Walter J. , Seibel Philip S. , Park Chong S. , Reichek Nathaniel
Published: December 2017

The effect of β-blockade on left ventricular (LV) remodeling, when added to angiotensin-converting enzyme inhibition (ACEI) after anterior myocardial infarction (MI), is incompletely understood. On day 2 after coronary ligation-induced anteroapical infarction, 17 sheep were randomized to ramipril (ACEI, n = 8) or ramipril and metoprolol (ACEI-β, n = 9). Magnetic resonance imaging was performed before and 8 wk after MI to measure changes in LV end-diastolic, end-systolic, and stroke volume indexes, LV mass index, ejection fraction (EF), and regional percent intramyocardial circumferential shortening.123I-labeled m-iodobenzylguanidine (MIBG) and fluorescent microspheres before and after adenosine were infused before death at 8 wk post-MI for quantitation of sympathetic innervation, blood flow, and blood flow reserve in adjacent and remote noninfarcted regions. Infarct size, regional blood flow, blood flow reserve, and the increase in LV mass and LV end-diastolic and end-systolic volume indexes were similar between groups. However, EF fell less over the 8-wk study period in the ACEI-β group (−13 ± 11 vs. −22 ± 4% in ACEI, P < 0.05). The ratio of adjacent to remote region123I-MIBG uptake was greater in ACEI-β animals than in the ACEI group (0.93 ± 0.06 vs. 0.86 ± 0.07, P < 0.04). When added to ACE inhibition after transmural anteroapical MI, β-blockade improves EF and adjacent regional sympathetic innervation but does not alter LV size.
Enhanced β-receptor-mediated vasorelaxation in hypoxic porcine coronary artery
Authors: Fukuda Satoru , Toriumi Takashi , Xu Hui , Kinoshita Hidenori , Nishimaki Hironobu , Kokubun Seiichiro , Fujiwara Naoshi , Fujihara Hideyoshi , Shimoji Koki
Published: December 2017

To investigate the β-adrenoceptor-mediated responses in hypoxic coronary arteries, we studied the effect of isoproterenol (Iso) on isolated porcine coronary arteries contracted with endothelin-1 in media aerated with 0, 5, 7.5, and 95% O2. The concentration-response curve of Iso was significantly shifted to the left by hypoxia (0 and 5% O2). In oxygenated and hypoxic arteries, 3 × 10−8, 10−6, and 10−5M Iso significantly increased the contents of cAMP. However, there was no difference in the increases of cAMP content induced by 3 × 10−8M Iso between oxygenated and hypoxic arteries. The content of cAMP induced by high concentrations of Iso (10−6and 10−5M) was significantly larger in hypoxic than in oxygenated arteries. Furthermore, the potentiation by hypoxia of the Iso-induced vasorelaxation was inhibited by glibenclamide and depolarization by KCl, but not by removal of endothelium and indomethacin. The vasodilatory response to forskolin and dibutyryl cAMP was unaffected by hypoxia. We conclude that activation of the ATP-sensitive K+channel may account for the potentiation of the response to Iso in hypoxic coronary arteries.
Computer-controlled heart rate increase by isoproterenol infusion: mathematical modeling of the system
Authors: Leor-Librach Ron Joseph , Bobrovsky Ben-Zion , Eliash Sarah , Kaplinsky Elieser
Published: December 2017

The purpose of this study was mathematical modeling of the heart rate (HR) response to isoproterenol (Iso) infusion. We developed a computerized system for the controlled increase of HR by Iso, based on a modified proportional-integral controller. HR was measured in conscious, freely moving rats. We found that the steady-state HR can be described as a hyperbolic power function of the steady-state Iso flow rate. This dependence was coupled with a first-order difference equation to form a pharmacodynamic model that reliably describes the relationship between HR and Iso flow for any arbitrary form of Iso flow function. In simulation studies, we showed that the model continued to follow the HR curve from real-time experiments far beyond the initial “learning interval” from which its parameters were calculated. Our results suggest that the predictive ability and the simplicity of calculating the parameters render this pharmacodynamic model appropriate for use within future advanced, model-based, adaptive control systems and as a part of larger cardiovascular models.
Loss of GSH and thiol enzymes in endothelial cells exposed to sublethal concentrations of hypochlorous acid
Authors: Pullar Juliet M. , Winterbourn Christine C. , Vissers Margret C. M.
Published: December 2017

We investigated the effect of sublethal concentrations of hypochlorous acid (HOCl) on intracellular thiol groups. Exposure of human umbilical vein endothelial cells to HOCl caused a decrease in cell viability, with concentrations of ≤25 μM HOCl being sublethal. At these concentrations, we saw a loss of glutathione and total protein thiol groups. Of the thiol enzymes we investigated, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was particularly susceptible to inactivation, creatine kinase was moderately susceptible, and lactate dehydrogenase was unaffected by HOCl at the concentrations used. Similar results were obtained with HOCl generated over 30 min by myeloperoxidase. GAPDH activity could be regenerated on reincubation of cells in Hanks’ balanced salt solution or reduction with dithiothreitol. In contrast, glutathione loss was not reversible, and further decreased with time. Cellular ATP levels decreased with sublethal HOCl concentrations and this appeared to be unrelated to the inactivation of GAPDH. Our results demonstrate that intracellular thiol groups differ in their reactivity with HOCl and suggest that HOCl may be able to regulate specific cellular functions.
Growth-related changes in the influence of nitric oxide on arteriolar tone
Authors: Linderman J. R. , Boegehold M. A.
Published: December 2017

This study was designed to determine whether juvenile growth is accompanied by changes in the local influence of nitric oxide (NO) or prostaglandins on arteriolar tone. In vivo microscopy was used to study proximal arterioles in the spinotrapezius muscle of rats 4–5 wk (weanling), 7–8 wk (juvenile), and 11–12 wk (mature) of age. From 4 to 12 wk of age, arterioles underwent an increase in resting diameter (from 31 ± 2 to 49 ± 2 μm) and volume flow (from 7 ± 1 to 10 ± 1 nl/s) but a decrease in resting wall shear rate (from 1,901 ± 150 to 748 ± 50 s−1). NO synthase inhibition with N G-monomethyl-l-arginine (l-NMMA) had no effect on arteriolar diameters in weanling rats but reduced diameters by 14 ± 4% in juvenile rats and by 13 ± 4% in mature rats. Cyclooxygenase inhibition with meclofenamate reduced arteriolar diameters by a similar amount (13 ± 4 to 18 ± 3%) in all age groups. There were no age-related differences in arteriolar responsiveness to locally applied sodium nitroprusside or prostaglandin E2. Arteriolar responsiveness to ACh was also similar in all groups, but thel-NMMA-sensitive portion of this response was smaller in mature rats than in weanling rats. Elevation of flow-related shear stress caused arteriolar dilation in juvenile rats but not in weanling rats. These findings suggest that arteriolar smooth muscle responsiveness to NO or prostaglandins does not change during juvenile growth and that basally released vasodilator prostaglandins exert a constant influence on arteriolar tone throughout this period. Basal NO activity also modulates arteriolar tone in juvenile and mature rats but not in weanling rats. In contrast, agonist-stimulated NO release is prominent in weanling and juvenile rats but somewhat decreased in mature rats, where cyclooxygenase products also contribute to ACh induced dilation.
Endothelial cell nitric oxide production in acute chest syndrome
Authors: Hammerman Samuel I. , Klings Elizabeth S. , Hendra Katherine P. , Upchurch Gilbert R. , Rishikof David C. , Loscalzo Joseph , Farber Harrison W.
Published: December 2017

Acute chest syndrome (ACS) is the most common form of acute pulmonary disease associated with sickle cell disease. To investigate the possibility that alterations in endothelial cell (EC) production and metabolism of nitric oxide (NO) products might be contributory, we measured NO products from cultured pulmonary EC exposed to red blood cells and/or plasma from sickle cell patients during crisis. Exposure to plasma from patients with ACS caused a 5- to 10-fold increase in S-nitrosothiol (RSNO) and a 7- to 14-fold increase in total nitrogen oxide (NOx) production by both pulmonary arterial and microvascular EC. Increases occurred within 2 h of exposure to plasma in a concentration-dependent manner and were associated with increases in endothelial nitric oxide synthase (eNOS) protein and eNOS enzymatic activity, but not with changes in nitric oxide synthase (NOS) III or NOS II transcripts, inducible NOS (iNOS) protein nor iNOS enzymatic activity. RSNO and NOxincreased whether plasma was obtained from patients with ACS or other forms of vasoocclusive crisis. Furthermore, an oxidative state occurred and oxidative metabolites of NO, particularly peroxynitrite, were produced. These findings suggest that altered NO production and metabolism to damaging oxidative molecules contribute to the pathogenesis of ACS.
Diacylglycerol delays pHiovershoot after reperfusion and attenuates contracture in isolated, paced myocytes
Authors: Ito Kenta , Kagaya Yutaka , Ishizuka Takeshi , Ito Nobuhiko , Ishide Nobumasa , Shirato Kunio
Published: December 2017

Although protein kinase C (PKC) plays a pivotal role in ischemic preconditioning, it is not clear what the end effector is that protects the myocardium. In isolated, paced (1.25 Hz, 36–37°C) adult rat cardiomyocytes, the effects of PKC preactivation by diacylglycerol on cell motion, intracellular Ca2+concentration ([Ca2+]i; indo 1), and intracellular pH (pHi; seminaphthorhodafluor-1) during simulated ischemia-reperfusion (I/R) were investigated. The degree of reperfusion-induced contracture was significantly attenuated in the myocytes pretreated with 10 μM 1,2-dioctanoyl- sn-glycerol (DOG; n = 19) compared with the untreated myocytes ( n = 23, P < 0.02). There were no differences in twitch amplitude, end-diastolic [Ca2+]i, or peak-systolic [Ca2+]iduring I/R between the DOG-pretreated and untreated myocytes. Although there were no differences in pHiduring ischemia, the pHiovershoot during reperfusion was significantly delayed in the DOG-pretreated myocytes compared with the untreated myocytes ( n = 17 for each, P < 0.01). Chelerythrine completely abolished the favorable effects of DOG on the reperfusion-induced contracture and the pHiovershoot. These data suggest that diacylglycerol attenuates I/R injury in isolated, paced cardiomyocytes, which may be related to the slower pHiovershoot during reperfusion.
Differential regulation of DNA synthesis by nitric oxide and hydroxyurea in vascular smooth muscle cells
Authors: Bundy Ruth , Marczin Nándor , Chester Adrian H. , Yacoub Magdi
Published: December 2017

We investigated the influence of nitrovasodilators on DNA synthesis in cultured human aortic smooth muscle cells and explored the hypothesis that nitric oxide (NO) is directly involved in mediating the inhibitory effects of hydroxyurea on DNA synthesis. Both NO and hydroxyurea inhibited ongoing DNA synthesis and S phase progression in our cells. Exogenous deoxynucleosides partially reversed this inhibition, suggesting that ribonucleotide reductase is a primary target for both NO and hydroxyurea. Nitrovasodilators inhibited DNA synthesis by releasing NO, as detected by chemiluminescence and as shown by the reversal of DNA synthesis inhibition by NO scavengers. This inhibition appears to occur via a cGMP-independent mechanism. In contrast, hydroxyurea did not produce a detectable NO signal, and NO scavengers had no influence on its inhibition of DNA synthesis, suggesting that NO does not mediate the inhibitory action of hydroxyurea in our system. Furthermore, the action of nitrovasodilators and hydroxyurea on DNA synthesis differed according to redox sensitivity. The redox agents N-acetyl-l-cysteine and ascorbate reversed NO inhibition of DNA synthesis and had no effect on DNA synthesis inhibition caused by hydroxyurea.
Role of oxidant stress in cytokine-induced activation of NF-κB in human aortic smooth muscle cells
Authors: Hoare Ginette S. , Marczin Nandor , Chester Adrian H. , Yacoub Magdi H.
Published: December 2017

The transcription factor nuclear factor-κB (NF-κB) has been implicated in inflammatory and proliferative vascular mechanisms. Activated NF-κB has been documented in human atherosclerotic lesions, and its activation in human vascular smooth muscle cells (SMC) by cytokines has been reported. However, intracellular mechanisms mediating NF-κB activation in human SMC are poorly understood. The aim of this study was to explore the potential role of reactive oxygen species and oxidant stress as signaling events in cytokine-induced NF-κB activation. Western blot analysis revealed the presence of inhibitory protein I-κBα in resting human aortic SMC, which was rapidly phosphorylated and degraded on exposure to interleukin-1β (IL-1β) followed by NF-κB translocation to the nucleus. IL-1β had no effect on two measures of intracellular oxidant stress, fluorescence generated by the oxidation of 2′,7′-dichlorodihydrofluorescin to dichlorofluorescein (DCF) or changes in intracellular sulfhydryl content. N-acetylcysteine (NAC) a membrane-permeant antioxidant, which augmented intracellular sulfhydryl content and inhibited H2O2-induced DCF fluorescence, had no effect on cytokine-induced NF-κB activation. In contrast to NAC, the metal chelators pyrrolidine dithiocarbamate and diethyldithiocarbamate attenuated IL-1β-induced NF-κB activation but had no effect on intracellular sulfhydryl content. Treatment of the cells with the oxidant H2O2caused an increase in DCF fluorescence and decreased intracellular sulfhydryl content but had no effect on I-κBα or NF-κB. In conclusion, this study suggests that oxidant stress may not play a major role in cytokine-induced activation of NF-κB in human aortic SMC and that oxidants may not be primary activators of NF-κB in these cells.
Nitric oxide: role in venular permeability recovery after histamine challenge
Authors: Al-Naemi Hamda , Baldwin Ann L.
Published: December 2017

Histamine is an inflammatory mediator produced by mast cells that reside close to blood vessels. It causes a transient increase in venular permeability and stimulates endothelial production of nitric oxide (NO). In this study, we investigated the role that NO plays in the permeability recovery and evaluated the response of mast cells. The mesenteric microvasculature of anesthetized rats was suffused with 10−3M histamine for 3 min and then perfused with the NO donor sodium nitroprusside (SNP; 10−6M), the NO inhibitor NG-monomethyl-l-arginine (l-NMMA; 10−5M), its enantiomer (d-NMMA; 10−5M), or HEPES-buffered saline containing 0.5% BSA for 15 min. This was replaced by FITC-albumin for 3 min, followed by fixative. The vasculature was visualized using epifluorescence microscopy and was stained for mast cells. Preparations treated with histamine only showed discrete FITC-albumin leaks. Subsequent inhibition of NO increased venular FITC-albumin leaks and prevented permeability recovery, whereas subsequent treatment with SNP decreased the histamine-induced venular leaks. Mast cells degranulated due to histamine and the other treatment combinations. In conclusion, inhibition of NO prevented permeability recovery and depleted mast cells of their histamine content.
Functional role of ionic regulation of Na+/Ca2+ exchange assessed in transgenic mouse hearts
Authors: Maxwell Krista , Scott Jason , Omelchenko Alexander , Lukas Anton , Lu Liyan , Lu Yujuan , Hnatowich Mark , Philipson Kenneth D. , Hryshko Larry V.
Published: December 2017

Na+/Ca2+exchange is the primary mechanism mediating Ca2+ efflux from cardiac myocytes during diastole and, thus, can prominently influence contractile force. In addition to transporting Na+and Ca2+, the exchanger is also regulated by these ions. Although structure-function studies have identified protein regions of the exchanger subserving these regulatory processes, their physiological importance is unknown. In this study, we examined the electrophysiological and mechanical consequences of cardiospecific overexpression of the canine cardiac exchanger NCX1.1 and a deletion mutant of NCX1.1 (Δ680–685), devoid of intracellular Na+([Formula: see text])- and Ca2+([Formula: see text])- dependent regulatory properties, in transgenic mice. Using the giant excised patch-clamp technique, normal ionic regulation was observed in membrane patches from cardiomyocytes isolated from control and transgenic mice overexpressing NCX1.1. In contrast, ionic regulation was nearly abolished in mice overexpressing Δ680–685, indicating that the native regulatory processes could be overwhelmed by expression of the transgene. To address the physiological consequences of ionic regulation of the Na+/Ca2+exchanger, we examined postrest force development in papillary muscles from NCX1.1 and Δ680–685 transgenic mice. Postrest potentiation was found to be substantially greater in Δ680–685 than in NCX1.1 transgenic mice, supporting the notion that ionic regulation of Na+/Ca2+exchange plays a significant functional role in cardiac contractile properties.
A force transducer for measuring mechanical properties of single cardiac myocytes
Authors: Tasche C. , Meyhöfer E. , Brenner B.
Published: December 2017

We have described a transducer design capable of recording forces generated by single cardiac myocytes with sufficient temporal resolution to detect force responses to rapid length changes. Our force sensors were made from thin steel foils that act as cantilevers whose bending is monitored by reflection off a laser beam. Deflection of the laser beam is measured by a differential photodiode detector. A small, 50-μm-thick tungsten needle attached to the free end of the steel foil allowed us to glue single cardiac cells to the force transducer. The transducers have compliances of ∼0.02 m/N and resonance frequencies between 2 and 3 kHz. The resolution is ∼18 nN rms at a detector bandwidth of 16 kHz, so we were able to resolve 0.2% of the maximum isometric force (∼12 μN) developed by a single cardiac myocyte. We have demonstrated that the transducer is well suited to analysis of mechanical properties of single ventricular myocytes, for example, the recording of isometric forces and rate constants of force redevelopment after rapid release-restretch maneuvers.
Rabbit heart can be “preconditioned” via transfer of coronary effluent
Authors: Dickson Eric W. , Lorbar Mojca , Porcaro William A. , Fenton Richard A. , Reinhardt Christopher P. , Gysembergh Anne , Przyklenk Karin
Published: December 2017

Brief myocardial ischemia not only evokes a local cardioprotective or “preconditioning” effect but also can render remote myocardium resistant to sustained ischemia. We propose the following hypotheses: remote protection is initiated by a humoral trigger; brief ischemia-reperfusion will result in release of the humoral trigger (possibly adenosine and/or norepinephrine) into the coronary effluent; and transfer of this effluent to a virgin acceptor heart will elicit cardioprotection. To test these concepts, effluent was collected during normal perfusion from donor-control hearts and during preconditioning ischemia-reperfusion from donor-preconditioned (PC) hearts. After reoxygenation occurred and aliquots for measurement of adenosine and norepinephrine content were harvested, effluent was transfused to acceptor-control and acceptor-PC hearts. All hearts then underwent 40 min of global ischemia and 60 min of reperfusion, and infarct size was delineated by tetrazolium staining. Mean infarct size was smaller in both donor- and acceptor-PC groups (9% of left ventricle) than in donor- and acceptor-control groups (36% and 34%; P < 0.01). Protection in acceptor-PC hearts could not, however, be attributed to adenosine or norepinephrine. Thus preconditioning-induced cardioprotection can be transferred between rabbit hearts by transfusion of coronary effluent. Although adenosine and norepinephrine are apparently not responsible, these results suggest that remote protection is initiated by a humoral mechanism.
Endotoxin and ischemic preconditioning: TNF-α concentration and myocardial infarct development in rabbits
Authors: Belosjorow Sergej , Schulz Rainer , Dörge Hilmar , Schade F. Ulrich , Heusch Gerd
Published: December 2017

Ischemic preconditioning (IP) and prior exposure to lipopolysaccharides (LPS) reduce infarct size (IS) and serum tumor necrosis factor-α (TNF-α) concentration resulting from myocardial ischemia-reperfusion in rabbits. The decrease in TNF-α might relate to an induced TNF-α inhibitory serum activity (TNF-α-ISA). We analyzed TNF-α and TNF-α-ISA during 30 and 180 min ischemia and reperfusion, respectively, in anesthetized rabbits either untreated ( group 1, n = 7), preconditioned (5 and 10 min ischemia and reperfusion, respectively, group 2, n = 9), or exposed to LPS 72 h before ischemia ( group 3, n = 9). TNF-α-ISA was assessed by coincubating LPS-stimulated rabbit blood with serum of groups 1–3 and measuring TNF-α (WEHI assay). With a comparable area at risk, IS in group 1 was 36.9 ± 11.1 (SD)%, and it was reduced to 13.1 ± 11.6% and 17.3 ± 11.3% (both P < 0.05) in groups 2 and 3, respectively. TNF-α was increased during ischemia-reperfusion in group 1 but remained unchanged in rabbits subjected to IP or LPS. TNF-α-ISA was detected during ischemia-reperfusion in group 2 (29% and 38% of maximum inhibition, respectively) and during baseline, ischemia and reperfusion in group 3 (51%, 46%, 48% of maximum inhibition, respectively) but was absent in group 1. Cardioprotection by IP and LPS is associated with a reduced TNF-α and an induced TNF-α-ISA during ischemia-reperfusion.
Nitroglycerin induces late preconditioning against myocardial stunning via a PKC-dependent pathway
Authors: Banerjee Supratim , Tang Xian-Liang , Qiu Yumin , Takano Hitoshi , Manchikalapudi Srinivas , Dawn Buddhadeb , Shirk Gregg , Bolli Roberto
Published: December 2017

Previous studies have shown that administration of nitric oxide (NO) donors induces a delayed cardioprotective effect indistinguishable from the late phase of ischemic preconditioning (PC). However, the ability of clinically relevant NO donors to elicit this phenomenon has not been evaluated. In this study we tested whether an NO-releasing agent that is nitroglycerin (NTG), which is widely used clinically, can mimic the late phase of ischemic PC. Four groups of conscious rabbits underwent six cycles of 4-min occlusion (O)/4-min reperfusion (R) for 3 consecutive days ( days 1, 2, and 3). The severity of myocardial stunning was assessed as the total deficit of systolic wall thickening (WTh) after the last O/R cycle. In the control group ( group I, n = 6), the total deficit of WTh was reduced by 50% and 51% on days 2 and 3 vs. day 1, respectively, indicating late PC against stunning. Pretreatment with NTG (2 μg ⋅ kg−1 ⋅ min−1iv over 1 h) on day 0 ( group II, n = 6) was as effective as ischemic PC in mitigating myocardial stunning 24 h later ( day 1); on days 2 and 3, no further reduction of stunning was seen. Coadministration of the PKC inhibitor chelerythrine (5 mg/kg) with NTG ( group III, n = 6) completely abrogated the NTG-induced protection. Pretreatment with chelerythrine alone ( group IV, n = 5) did not alter stunning. These results demonstrate that a relatively brief infusion of NTG induces a robust protective effect against stunning 24 h later via a protein kinase C (PKC)-dependent signaling mechanism. The magnitude of NTG-induced protection is equivalent to that observed during the late phase of ischemic PC. Late PC induced by brief treatment with NTG could be a useful therapeutic strategy for myocardial protection in patients with ischemic heart disease.
Nitric oxide donors attenuate myocardial stunning in conscious rabbits
Authors: Shinmura Ken , Tang Xian-Liang , Takano Hitoshi , Hill Michael , Bolli Roberto
Published: December 2017

Although previous studies suggested that the protection of late preconditioning (PC) against myocardial stunning is mediated by nitric oxide (NO), direct evidence that exogenous administration of NO attenuates myocardial stunning is lacking. Furthermore, although exogenous NO administration was shown to elicit a late PC phase, it is unknown whether NO donors also induce an early PC phase. Therefore, conscious rabbits underwent two experimental stages (3 days of six 4-min occlusion/4-min reperfusion cycles each) 2 wk apart. In study I, both stages were control stages ( n = 7). In studies II and III, stage I was the control stage. On day 1of stage II, seven rabbits received infusion of nitroglycerin (NTG; 2 μg ⋅ kg−1⋅ min−1iv) during the ischemia-reperfusion sequence, starting 30 min before the 1st occlusion and ending 10 min after the 6th reperfusion ( study II). Another seven rabbits received infusion of NTG (2 μg ⋅ kg−1⋅ min−1iv) for 1 h followed by a 30-min washout interval and then underwent six 4-min occlusion/4-min reperfusion cycles ( study III). In the control stage of all three studies, recovery of wall thickening (WTh) after occlusion/reperfusion cycles was markedly enhanced on days 2 and 3 compared with day 1, indicating late PC. In study II, infusion of NTG during the occlusion/reperfusion cycles on day 1 resulted in significant and sustained enhancement in WTh recovery. A similar attenuation of stunning was observed in study IV in six rabbits given intravenous infusion of S-nitroso- N-acetylpenicillamine (SNAP) during occlusion/reperfusion cycles. The magnitude of the protection afforded by NTG and SNAP was comparable to that afforded by the late ischemic PC phase. In contrast, in study III infusion of NTG before occlusion/reperfusion cycles did not enhance WTh recovery, indicating that NTG failed to induce an early PC effect against stunning. This study demonstrates that administration of hemodynamically inactive doses of two unrelated NO donors alleviates myocardial stunning in conscious rabbits, providing direct evidence for a protective action of NO in this setting.
Modified heart-lung preparation for the evaluation of systolic and diastolic coronary flow in rats
Authors: Kissling G. , Blickle B. , Pascht U.
Published: December 2017

A modified heart-lung preparation of the rat, which permits measuring systolic and diastolic coronary flow separately and enables coronary compliance to be evaluated, is described. The systemic circulation was substituted by a shunt circuit, and the elastic properties of the arterial tree were mimicked by a rubber balloon. Systolic and diastolic coronary flow was evaluated from the pulmonary and aortic flow signal. Integrated phasic pulmonary flow represented right ventricular stroke volume. Integrated phasic systolic aortic flow represented left ventricular stroke volume minus that volume flowing into the coronary arteries during systole, because the aortic flow probe had to be inserted distal to the origin of the coronary vessels. Because right and left ventricular stroke volume was identical under steady-state conditions, the difference between systolic pulmonary and systolic aortic flow resulted in systolic coronary flow. Diastolic coronary flow was measured by means of the retrograde flow through the aortic flow probe. Coronary compliance was calculated according to Frank's windkessel model from coronary resistance and from central diastolic aortic pressure, which decayed exponentially after switching out the rubber balloon and the shunt circuit. It could be shown that the proportion of systolic to diastolic coronary flow depends on coronary compliance.
Capillary endothelial surface layer selectively reduces plasma solute distribution volume
Authors: Vink Hans , Duling Brian R.
Published: December 2017

We previously reported that a 0.4- to 0.5-μm-thick endothelial surface layer confines Dextran 70 (70 kDa) to the central core of hamster cremaster muscle capillaries. In the present study we used a variety of plasma tracers to probe the barrier properties of the endothelial surface layer using combined fluorescence and brightfield intravital microscopy. No permeation of the endothelial surface layer was observed for either neutral or anionic dextrans ≥70 kDa, but a neutral Dextran 40 (40 kDa) and neutral free dye (rhodamine, 0.4 kDa) equilibrated with the endothelial surface layer within 1 min. In contrast, small anionic tracers of similar size (0.4–40 kDa) permeated the endothelial surface layer relatively slowly with half-times (τ50) between 11 and 60 min, depending on tracer size. Furthermore, two plasma proteins, fibrinogen (340 kDa) and albumin (67 kDa), moved slowly into the endothelial surface layer at the same rates, despite greatly differing sizes (τ50 ≈ 40 min). Dextran 70, which did not enter the glycocalyx over the course of these experiments, entered at the same rate as free albumin when it was conjugated to albumin. These findings demonstrate that for anionic molecules size and charge have a profound effect on the penetration rate into the glycocalyx. The equal rates of penetration of the glycocalyx demonstrated by the different protein molecules suggests that multiple factors may influence the penetration of the barrier, including molecular size, charge, and structure.
Chronic hypercapnia inhibits hypoxic pulmonary vascular remodeling
Authors: Ooi Henry , Cadogan Elaine , Sweeney Michèle , Howell Katherine , O'Regan R. G. , McLoughlin Paul
Published: December 2017

Chronic hypercapnia is commonly found in patients with severe hypoxic lung disease and is associated with a greater elevation of pulmonary arterial pressure than that due to hypoxia alone. We hypothesized that hypercapnia worsens hypoxic pulmonary hypertension by augmenting pulmonary vascular remodeling and hypoxic pulmonary vasoconstriction (HPV). Rats were exposed to chronic hypoxia [inspiratory O2 fraction ([Formula: see text]) = 0.10], chronic hypercapnia (inspiratory CO2 fraction = 0.10), hypoxia-hypercapnia ([Formula: see text]= 0.10, inspiratory CO2 fraction = 0.10), or room air. After 1 and 3 wk of exposure, muscularization of resistance blood vessels and hypoxia-induced hematocrit elevation were significantly inhibited in hypoxia-hypercapnia compared with hypoxia alone ( P < 0.001, ANOVA). Right ventricular hypertrophy was reduced in hypoxia-hypercapnia compared with hypoxia at 3 wk ( P < 0.001, ANOVA). In isolated, ventilated, blood-perfused lungs, basal pulmonary arterial pressure after 1 wk of exposure to hypoxia (20.1 ± 1.8 mmHg) was significantly ( P < 0.01, ANOVA) elevated compared with control conditions (12.1 ± 0.1 mmHg) but was not altered in hypoxia-hypercapnia (13.5 ± 0.9 mmHg) or hypercapnia (11.8 ± 1.3 mmHg). HPV ([Formula: see text] = 0.03) was attenuated in hypoxia, hypoxia-hypercapnia, and hypercapnia compared with control ( P < 0.05, ANOVA). Addition of N ω-nitro-l-arginine methyl ester (10−4 M), which augmented HPV in control, hypoxia, and hypercapnia, significantly reduced HPV in hypoxia-hypercapnia. Chronic hypoxia caused impaired endothelium-dependent relaxation in isolated pulmonary arteries, but coexistent hypercapnia partially protected against this effect. These findings suggest that coexistent hypercapnia inhibits hypoxia-induced pulmonary vascular remodeling and right ventricular hypertrophy, reduces HPV, and protects against hypoxia-induced impairment of endothelial function.
VSM growth is stimulated in sympathetic neuron/VSM cocultures: role of TGF-β2 and endothelin
Authors: Damon Deborah H.
Published: December 2017

Sympathetic nerves are purported to stimulate blood vessel growth. The mechanism(s) underlying this stimulation has not been determined. With use of an in vitro coculture model, the present study tests the hypothesis that sympathetic neurons stimulate the growth of vascular smooth muscle (VSM) and evaluates potential mechanisms mediating this stimulation. Sympathetic neurons isolated from superior cervical ganglia (SCG) stimulated the growth of VSM. Growth of VSM in the presence of SCG (856 ± 81%) was significantly greater than that in the absence of SCG (626 ± 66%, P < 0.05). SCG did not stimulate VSM growth in transwell cocultures. An antibody that neutralized the activity of transforming growth factor-β2 (TGF-β2) inhibited SCG stimulation of VSM growth in coculture. SCG stimulation of VSM growth was also inhibited by an endothelin A receptor antagonist. These data suggest novel mechanisms for sympathetic modulation of vascular growth that may play a role in the physiological and/or pathological growth of the vasculature.
Role of leukocytes and tissue-derived oxidants in short-term skeletal muscle ischemia-reperfusion injury
Authors: Kadambi Ananth , Skalak Thomas C.
Published: December 2017

The relative contribution of xanthine oxidase (XO) and leukocytes to tissue injury after short-term ischemia is unknown. In this study, we subjected three groups of rat spinotrapezius muscles to 30-min ischemia and 1-h reperfusion: 1) ischemia-reperfusion (I/R) + 0.9% saline, 2) I/R + superoxide dismutase, and 3) I/R + oxypurinol. A fourth group served as nonischemic control. We quantified the increase in resistance (%Δ R) caused by leukocyte-capillary plugging concurrently with myocyte uptake of propidium iodide (PI) [expressed as no. of PI spots per total volume of perfused tissue ( N PI/V)] and performed assays to quantify XO activity, thiobarbituric acid-reactive substances (TBARS), and myeloperoxidase (MPO). Groups 2 and 3 exhibited significant decreases in N PI/V relative to group 1. MPO levels and TBARS were similar among all groups, and mean %Δ R was significantly reduced in groups 2 and 3 relative to group 1. However, elevated XO was observed in groups 1 and 2 relative to group 3 and nonischemic controls. These data are consistent with the hypothesis that XO, rather than toxic species produced by plugging or venule-adherent leukocytes, is responsible for postischemic damage in this model.
Measurements of calcium transients in ventricular cells during discontinuous action potential conduction
Authors: Wagner Mary B. , Wang Yang-Gan , Kumar Rajiv , Golod David A. , Goolsby William N. , Joyner Ronald W.
Published: December 2017

The L-type calcium current ( I Ca) is important in sustaining propagation during discontinuous conduction. In addition, I Ca is altered during discontinuous conduction, which may result in changes in the intracellular calcium transient. To study this, we have combined the ability to monitor intracellular calcium concentration ([Ca2+]i) in an isolated cardiac cell using confocal scanning laser fluorescence microscopy with our “coupling clamp” technique, which allows action potential propagation from the real cell to a real-time simulation of a model cell. Coupling a real cell to a model cell with a value of coupling conductance ( G C = 8 nS) just above the critical value for action potential propagation results in both an increased amplitude and an increased rate of rise of the calcium transient. Similar but smaller changes in the calcium transient are caused by increasing G C to 20 nS. The increase of [Ca2+]i by discontinuous conduction is less than the increase of I Ca, which may indicate that much of [Ca2+]i is the result of calcium released from the sarcoplasmic reticulum rather than the integration of I Ca.
Relationship between nociceptin/orphanin FQ and cerebral hemodynamics after hypoxia-ischemia in piglets
Authors: Armstead William M.
Published: December 2017

This study was designed to characterize the role of the newly described endogenous opioid nociceptin/orphanin FQ (NOC/oFQ) in reduced cerebral blood flow (CBF) observed after ischemia-reperfusion (I/R) and combined hypoxia and ischemia-reperfusion (H-I/R), as a function of time after onset of reperfusion in newborn pigs equipped with a closed cranial window. Global cerebral ischemia (20 min) was induced via elevation of intracranial pressure, whereas hypoxia (10 min) decreased[Formula: see text] to 35 ± 3 mmHg with unchanged[Formula: see text]. I/R elevated cerebrospinal fluid (CSF) NOC/oFQ from 67 ± 4 to 266 ± 29 pg/ml within 1 h, whereas values returned to control level within 4 h of reperfusion. H-I/R elevated CSF NOC/oFQ to 483 ± 67 pg/ml within 1 h, and such values returned slowly to control level within 12 h of reperfusion. Topical NOC/oFQ (10− 8 M, 10− 6 M)-induced vasodilation was attenuated by I/R and reversed to vasoconstriction by H-I/R at 1 h of reperfusion (control, 9 ± 1 and 16 ± 1%; I/R, 3 ± 1 and 6 ± 1%; H-I/R, −6 ± 1 and −11 ± 1%). Such altered dilation returned to control values within 4 h in I/R animals and within 12 h in H-I/R animals. Blood flow in the cerebrum was reduced from 58 ± 4 to 33 ± 2 ml ⋅ min− 1 ⋅ 100 g− 1 within 1 h and returned to control value within 4 h in I/R animals. In animals pretreated with [F/G]NOC/oFQ(1–13)-NH2 (1 mg/kg iv), an NOC/oFQ antagonist, however, CBF only fell to 43 ± 3 ml ⋅ min− 1 ⋅ 100 g− 1 at 1 h of reperfusion. Similar observations were made in H-I/R animals. These data suggest that an elevated CSF NOC/oFQ concentration and altered vascular responsiveness to this opioid contribute to reductions in CBF observed after either I/R or H-I/R.
A novel servo-control system that imposes desired aortic input impedance on in situ rat heart
Authors: Miyashita Hiroshi , Sugimachi Masaru , Sato Takayuki , Kawada Toru , Shishido Toshiaki , Nakahara Tsutomu , Yoshimura Ryoichi , Takaki Hiroshi , Miyano Hiroshi , Sunagawa Kenji
Published: December 2017

To clarify the pathophysiological role of dynamic arterial properties in cardiovascular diseases, we attempted to develop a new control system that imposes desired aortic impedance on in situ rat left ventricle. In 38 anesthetized open-chest rats, ascending aortic pressure and flow waveforms were continuously sampled (1,000 Hz). Desired flow waveforms were calculated from measured aortic pressure waveforms and target impedance. To minimize the difference between measured and desired aortic flow waveforms, the computer generated commands to the servo-pump, connected to a side branch of the aorta. By iterating the process, we could successfully control aortic impedance in such a way as to manipulate compliance and characteristic impedance between 60 and 160% of their respective native values. The error between desired and measured aortic flow waveforms was 70 ± 34 μl/s (root mean square; 4.4 ± 1.4% of peak flow), indicating reasonable accuracy in controlling aortic impedance. This system enables us to examine the importance of dynamic arterial properties independently of other hemodynamic and neurohumoral factors in physiological and clinical settings.