bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of circulatory and intestinal barrier dysfunction during whole body hyperthermia
Authors: Hall David M. , Buettner Garry R. , Oberley Larry W. , Xu Linjing , Matthes Ronald D. , Gisolfi Carl V.
Published: December 2017

This work tested the hypotheses that splanchnic oxidant generation is important in determining heat tolerance and that inappropriate ·NO production may be involved in circulatory dysfunction with heat stroke. We monitored colonic temperature (Tc), heart rate, mean arterial pressure, and splanchnic blood flow (SBF) in anesthetized rats exposed to 40°C ambient temperature. Heating rate, heating time, and thermal load determined heat tolerance. Portal blood was regularly collected for determination of radical and endotoxin content. Elevating Tc from 37 to 41.5°C reduced SBF by 40% and stimulated production of the radicals ceruloplasmin, semiquinone, and penta-coordinate iron(II) nitrosyl-heme (heme-·NO). Portal endotoxin concentration rose from 28 to 59 pg/ml ( P < 0.05). Compared with heat stress alone, heat plus treatment with the nitric oxide synthase (NOS) antagonist N ω-nitro-l-arginine methyl ester (l-NAME) dose dependently depressed heme-·NO production and increased ceruloplasmin and semiquinone levels. l-NAME also significantly reduced lowered SBF, increased portal endotoxin concentration, and reduced heat tolerance ( P < 0.05). The NOS II and diamine oxidase antagonist aminoguanidine, the superoxide anion scavenger superoxide dismutase, and the xanthine oxidase antagonist allopurinol slowed the rates of heme-·NO production, decreased ceruloplasmin and semiquinone levels, and preserved SBF. However, only aminoguanidine and allopurinol improved heat tolerance, and only allpourinol eliminated the rise in portal endotoxin content. We conclude that hyperthermia stimulates xanthine oxidase production of reactive oxygen species that activate metals and limit heat tolerance by promoting circulatory and intestinal barrier dysfunction. In addition, intact NOS activity is required for normal stress tolerance, whereas overproduction of ·NO may contribute to the nonprogrammed splanchnic dilation that precedes vascular collapse with heat stroke.
Electrophysiological heterogeneity and stability of reentry in simulated cardiac tissue
Authors: Xie Fagen , Qu Zhilin , Garfinkel Alan , Weiss James N.
Published: December 2017

Generation of wave break is a characteristic feature of cardiac fibrillation. In this study, we investigated how dynamic factors and fixed electrophysiological heterogeneity interact to promote wave break in simulated two-dimensional cardiac tissue, by using the Luo-Rudy (LR1) ventricular action potential model. The degree of dynamic instability of the action potential model was controlled by varying the maximal amplitude of the slow inward Ca2+ current to produce spiral waves in homogeneous tissue that were either nearly stable, meandering, hypermeandering, or in breakup regimes. Fixed electrophysiological heterogeneity was modeled by randomly varying action potential duration over different spatial scales to create dispersion of refractoriness. We found that the degree of dispersion of refractoriness required to induce wave break decreased markedly as dynamic instability of the cardiac model increased. These findings suggest that reducing the dynamic instability of cardiac cells by interventions, such as decreasing the steepness of action potential duration restitution, may still have merit as an antifibrillatory strategy.
Targeted inactivation of Gαidoes not alter cardiac function or β-adrenergic sensitivity
Authors: Jain Mohit , Lim Chee Chew , Nagata Kohzo , Davis Vannessa M. , Milstone David S. , Liao Ronglih , Mortensen Richard M.
Published: December 2017

Inhibitory Gαiprotein increases in the myocardium during hypertrophy and has been associated with β-adrenergic receptor (β-AR) desensitization, contractile dysfunction, and progression of cardiac disease. The role of Gαiproteins in mediating basal cardiac function and β-AR response in nonpathological myocardium, however, is uncertain. Transgenic mice with targeted inactivation of Gαi2or Gαi3were examined for in vivo cardiac function with the use of conscious echocardiography and for ex vivo cardiac response to inotropic stimulation with the use of Langendorff blood-perfused isolated hearts and adult ventricular cardiomyocytes. Echocardiography revealed that percent fractional shortening and heart rate were similar among wild-type, Gαi2-null, and Gαi3-null mice. Comparable baseline diastolic and contractile performance was also observed in isolated hearts and isolated ventricular myocytes from wild-type mice and mice lacking Gαiproteins. Isoproterenol infusion enhanced diastolic and contractile performance to a similar degree in wild-type, Gαi2-null, and Gαi3-null mice. These data demonstrate no observable role for inhibitory G proteins in mediating basal cardiac function or sensitivity to β-AR stimulation in nonpathological myocardium.
Adenosine-enhanced ischemic preconditioning: adenosine receptor involvement during ischemia and reperfusion
Authors: McCully James D. , Toyoda Yoshiya , Uematsu Masahisa , Stewart Robert D. , Levitsky Sidney
Published: December 2017

Adenosine-enhanced ischemic preconditioning (APC) extends the cardioprotection of ischemic preconditioning (IPC) by both significantly decreasing myocardial infarct size and significantly enhancing postischemic functional recovery. In this study, the role of adenosine receptors during ischemia-reperfusion was determined. Rabbit hearts ( n = 92) were used for Langendorff perfusion. Control hearts were perfused for 180 min, global ischemia hearts received 30-min ischemia and 120-min reperfusion, and IPC hearts received 5-min ischemia and 5-min reperfusion before ischemia. APC hearts received a bolus injection of adenosine coincident with IPC. Adenosine receptor (A1, A2, and A3) antagonists were used with APC before ischemia and/or during reperfusion. GR-69019X (A1/A3) and MRS-1191/MRS-1220 (A3) significantly increased infarct size in APC hearts when administered before ischemia and significantly decreased functional recovery when administered during both ischemia and reperfusion ( P < 0.05 vs. APC). DPCPX (A1) administered either before ischemia and/or during reperfusion had no effect on APC cardioprotection. APC-enhanced infarct size reduction is modulated by adenosine receptors primarily during ischemia, whereas APC-enhanced postischemic functional recovery is modulated by adenosine receptors during both ischemia and reperfusion.
Molecular mechanisms of ATP and insulin synergistic stimulation of coronary artery smooth muscle growth
Authors: Agazie Yehenew M. , Bagot J. Courtney , Trickey Erica , Halenda Stephen P. , Wilden Peter A.
Published: December 2017

Coronary artery disease (CAD) is the major cause of death in diabetics. Abnormal proliferation of coronary artery smooth muscle cells (CASMC) leads to intimal thickening in CAD. We examined signaling mechanisms involved in the mitogenic effect of ATP and insulin on CASMC. ATP and insulin individually stimulated DNA synthesis by 4- and 2-fold, respectively; however, they acted synergistically to stimulate an increase of 17-fold over basal. A similar synergistic stimulation of extracellular signal-regulated kinase (ERK) and mitogen-activated protein or ERK kinase activities was observed (ATP, 7-fold; insulin, 2-fold; and ATP + insulin, 16-fold over basal). However, the combination of ATP and insulin stimulated only an additive activation of Raf (ATP, 5-fold; insulin, <2-fold; and ATP + insulin, 8-fold over basal) and Ras (ATP, 5-fold; insulin, 2-fold; and ATP + insulin, 8-fold over basal). Thus convergence of ATP and insulin signals appears to be at the level of Ras and Raf. In addition, insulin stimulated activation of Akt (also known as protein kinase B) (10-fold over basal), whereas ATP had little effect. However, when ATP and insulin were added in combination, ATP dramatically reduced the insulin-stimulated Akt activation (2-fold above basal). Thus these results are consistent with ATP relieving an insulin-induced Akt-dependent inhibitory effect on the ERK signaling pathway, leading to synergistic stimulation of CASMC proliferation.
Increasedl-arginine uptake and inducible nitric oxide synthase activity in aortas of rats with heart failure
Authors: Stathopulos Peter B. , Lu Xiangru , Shen Ji , Scott Jeremy A. , Hammond James R. , McCormack David G. , Arnold J. Malcolm O. , Feng Qingping
Published: December 2017

l-Arginine crosses the cell membrane primarily through the system y+transporter. The aim of this study was to investigate the role of l-arginine transport in nitric oxide (NO) production in aortas of rats with heart failure induced by myocardial infarction. Tumor necrosis factor-α levels in aortas of rats with heart failure were six times higher than in sham rats ( P < 0.01). l-Arginine uptake was increased in aortas of rats with heart failure compared with sham rats ( P < 0.01). Cationic amino acid transporter-2B and inducible (i) nitric oxide synthase (NOS) expression were increased in aortas of rats with heart failure compared with sham rats ( P < 0.05). Aortic strips from rats with heart failure treated with l-arginine but not d-arginine increased NO production ( P < 0.05). The effect ofl-arginine on NO production was blocked byl-lysine, a basic amino acid that shares the same system y+transporter withl-arginine, and by the NOS inhibitor NG-nitro-l-arginine methyl ester (l-NAME). Treatment with l-lysine andl-NAME in vivo decreased plasma nitrate and nitrite levels in rats with heart failure ( P < 0.05). Our data demonstrate that NO production is dependent on iNOS activity andl-arginine uptake and suggest that l-arginine transport plays an important role in enhanced NO production in heart failure.
Effects of exercise and passive head-up tilt on fractal and complexity properties of heart rate dynamics
Authors: Tulppo Mikko P. , Hughson Richard L. , Mäkikallio Timo H. , Airaksinen K. E. Juhani , Seppänen Tapio , Huikuri Heikki V.
Published: December 2017

tk;1Passive head-up tilt and exercise result in specific changes in the spectral characteristics of heart rate (HR) variability as a result of reduced vagal and enhanced sympathetic outflow. Recently analytic methods based on nonlinear system theory have been developed to characterize the nonlinear features in HR dynamics. This study was designed to assess the changes in the fractal and complexity measures of HR behavior during the passive head-up tilt and during exercise. Fractal exponent (α1) and approximate entropy (ApEn), measures of short-term correlation properties and overall complexity of HR, respectively, along with spectral components of HR variability were analyzed during a passive head-up tilt test ( n = 10) and a low-intensity steady-state exercise ( n = 20) in healthy subjects. We observed that α1 increased during the tilt test (from 0.85 ± 0.22 to 1.48 ± 0.20; P < 0.001) and during the exercise (from 1.00 ± 0.22 to 1.37 ± 0. 14; P < 0.001). ApEn also increased during the exercise (from 1.04 ± 0.11 to 1. 11 ± 0.08; P < 0.05), but it did not change during the tilt test. The normalized high-frequency spectral component decreased and the low-frequency component increased similarly during both the exercise and the tilt test ( P < 0.001 for all). Exercise and passive tilt result in an increase of short-term fractal correlation properties of HR dynamics, which is related to changes in the balance between the low- and high-frequency oscillations in controlled situations. Overall complexity of HR dynamics increases during exercise but not during passive tilt.
Involvement of nitric oxide in cardioprotective effect of endothelin receptor antagonist during ischemia-reperfusion
Authors: Gourine Andrey V. , Gonon Adrian T. , Pernow John
Published: December 2017

The interaction between the cardioprotective effect of endothelin (ET) receptor blockade and nitric oxide (NO) during ischemia-reperfusion injury was investigated. Anesthetized pigs were subjected to 45 ( protocol 1) or 30 min ( protocol 2) coronary artery ligation and 4 h reperfusion. In protocol 1, five groups were given vehicle, the ETA receptor antagonist LU-135252 (LU), the NO synthase (NOS) inhibitor N G-nitro-l-arginine (l-NNA), l-NNA in combination with LU, orl-NNA in combination with the NO precursorl-arginine (l-Arg) and LU intravenously before ischemia. In protocol 2, two groups were given vehicle or l-NNA. In protocol 1, the infarct size (IS) was 79 ± 5% of the area at risk in the vehicle group and 93 ± 2% in the l-NNA group. LU reduced the IS to 43 ± 7% ( P < 0.001). The cardioprotective effect of LU was abolished in the presence ofl-NNA (IS 76 ± 6%), whereas addition ofl-Arg restored its cardioprotective effect (IS 56 ± 2%; P < 0.05 vs. vehicle and l-NNA + LU groups). In protocol 2, the IS was 49 ± 6% in the vehicle group and 32 ± 4% in the l-NNA group ( P = not significant). Myocardial ET-like immunoreactivity (ET-LI) increased in the vehicle group of protocol 1. ET-LI in the ischemic-reperfused myocardium was lower in the groups given LU ( P < 0.01) and l-NNA + l-Arg + LU ( P < 0.05) but not in the group givenl-NNA + LU compared with the vehicle group. These results suggest that the cardioprotective effect of the ETAreceptor antagonist is mediated via a mechanism related to NO.
Branching exponent heterogeneity and wall shear stress distribution in vascular trees
Authors: Karau Kelly L. , Krenz Gary S. , Dawson Christopher A.
Published: December 2017

A bifurcating arterial system with Poiseuille flow can function at minimum cost and with uniform wall shear stress if the branching exponent ( z) = 3 [where z is defined by ( D 1) z = ( D 2) z + ( D 3) z ; D 1 is the parent vessel diameter and D 2 and D 3 are the two daughter vessel diameters at a bifurcation]. Because wall shear stress is a physiologically transducible force, shear stress-dependent control over vessel diameter would appear to provide a means for preserving this optimal structure through maintenance of uniform shear stress. A mean z of 3 has been considered confirmation of such a control mechanism. The objective of the present study was to evaluate the consequences of a heterogeneous distribution of z values about the mean with regard to this uniform shear stress hypothesis. Simulations were carried out on model structures otherwise conforming to the criteria consistent with uniform shear stress when z = 3 but with varying distributions of z. The result was that when there was significant heterogeneity in z approaching that found in a real arterial tree, the coefficient of variation in shear stress was comparable to the coefficient of variation in z and nearly independent of the mean value of z. A systematic increase in mean shear stress with decreasing vessel diameter was one component of the variation in shear stress even when the mean z = 3. The conclusion is that the influence of shear stress in determining vessel diameters is not, per se, manifested in a mean value of z. In a vascular tree having a heterogeneous distribution in zvalues, a particular mean value of z (e.g., z = 3) apparently has little bearing on the uniform shear stress hypothesis.
Early activation of IKKβ during in vivo myocardial ischemia
Authors: Li Chuanfu , Kao Race L. , Ha Tuanzhu , Kelley Jim , Browder I. William , Williams David L.
Published: December 2017

We have demonstrated that in vitro brief ischemia activates nuclear factor (NF)-κB in rat myocardium. We report in vivo ischemia-reperfusion (I/R)-induced NF-κB activation, IκB kinase -β (IKKβ) activity, and IκBα phosphorylation and degradation in rat myocardium. Rat hearts were subjected to occlusion of the coronary artery for up to 45 min or occlusion for 15 min followed by reperfusion for up to 3 h. Cytoplasmic and nuclear proteins were isolated from ischemic and nonischemic areas of each heart. NF-κB activation was increased in the ischemic area (680%) after 10 min of ischemia and in the nonischemic area (350%) after 15 min of ischemia and remained elevated during prolonged ischemia and reperfusion. IKKβ activity was markedly increased in ischemic (1,800%) and nonischemic (860%) areas, and phosphorylated IκBα levels were significantly elevated in ischemic (180%) and nonischemic (280%) areas at 5 min of ischemia and further increased after reperfusion. IκBα levels were decreased in the ischemic (45%) and nonischemic (36%) areas after 10 min of ischemia and remained low in the ischemic area during prolonged ischemia and reperfusion. The results suggest that in vivo I/R rapidly induces IKKβ activity and increases IκBα phosphorylation and degradation, resulting in NF-κB activation in the myocardium.
Coronary sinus occlusion enhances coronary collateral flow and reduces subendocardial ischemia
Authors: Ido Akira , Hasebe Naoyuki , Matsuhashi Hironobu , Kikuchi Kenjiro
Published: December 2017

On the hypothesis that coronary sinus occlusion (CSO) may reduce myocardial ischemia, we examined the effects of CSO on coronary collateral blood flow and on the distribution of regional myocardial blood flow (RMBF) in dogs. Thirty-eight anesthetized dogs underwent occlusion of the left anterior descending coronary artery with or without CSO and intact vasomotor tone. We measured RMBF and intramyocardial pressure (IMP) in the subendocardium (Endo) and subepicardium (Epi) separately. With intact vasomotor tone, CSO during ischemia significantly increased RMBF in the ischemic region (IR), particularly in Endo from 0.17 ± 0.03 to 0.33 ± 0.05 ml · min−1· g−1( P < 0.05), and increased the Endo/Epi from 0.59 ± 0.10 to 1.15 ± 0.15 ( P < 0.01). These effects of CSO were partially abolished by adenosine. However, the Endo/Epi was still increased from 0.90 ± 0.13 to 2.09 ± 0.30 ( P < 0.01). The changes in RMBF in IR were significantly correlated with the peak CS pressure during CSO. The Endo/Epi of IMP in IR was significantly decreased during CSO. In conclusion, CSO potentially enhances coronary collateral flow, and preserves the ischemic myocardium, especially in Endo.
Coupling interval from slow to tachycardiac pacing decides sustained alternans pattern
Authors: Suzuki Shunsuke , Araki Junichi , Doi Yumiko , Fujinaka Waso , Minami Hitoshi , Iribe Gentaro , Mohri Satoshi , Shimizu Juichiro , Hirakawa Masahisa , Suga Hiroyuki
Published: December 2017

We discovered that the coupling beat interval from a slow to a tachycardiac pacing period considerably affected the pattern of the beat-to-beat alternation of the tachycardia-induced sustained contractile alternans. We analyzed the relationship between the coupling interval and the pattern and amplitude of the alternans in the isovolumic left ventricle of canine blood-perfused hearts. The alternans pattern and amplitude varied transiently over the first 30–50 beats and became gradually stable over the first minute in all 12 hearts. We discovered that stable alternans, even under the same tachycardiac pacing, had three different strong-weak beat patterns depending on the coupling interval. A relatively short coupling interval produced a representative sustained alternans of the strong and weak beats. A relatively long coupling interval produced a similar sustained alternans but in a reversed order of even- and odd-numbered beats counted from the coupling interval. However, sustained alternans disappeared after 1–3 specific coupling intervals. We conclude that ventricular pacing rate does not solely determine the pattern and amplitude of sustained contractile alternans induced by tachycardia.
Physiological and anatomic evidence for regulation of the heart by suprachiasmatic nucleus in rats
Authors: Scheer F. A. J. L. , Ter Horst G. J. , van der Vliet J. , Buijs R. M.
Published: December 2017

The suprachiasmatic nucleus (SCN) is the mammalian biological clock that generates the daily rhythms in physiology and behavior. Light can phase shift the rhythm of the SCN but can also acutely affect SCN activity and output, e.g., output to the pineal. Recently, multisynaptic SCN connections to other organs were also demonstrated. Moreover, they were shown to affect those organs functionally. The aim of the present study was to investigate the role of the SCN in the regulation of the heart. First, we demonstrated that heart rate (HR) in SCN-intact, but not SCN-lesioned (SCNx), male Wistar rats had a clear circadian rhythm, which was not caused by locomotor activity. Second, we demonstrated that light at night reduces HR in intact but not in SCNx rats. Finally, we demonstrated the presence of a multisynaptic autonomic connection from SCN neurons to the heart with the retrograde pseudorabies virus tracing technique. Together, these results demonstrate that the SCN affects the heart in rats and suggest that this is mediated by a neuronal mechanism.
Both central command and exercise pressor reflex reset carotid sinus baroreflex
Authors: McIlveen Stephen A. , Hayes Shawn G. , Kaufman Marc P.
Published: December 2017

In decerebrate unanesthetized cats, we determined whether either “central command,” the exercise pressor reflex, or the muscle mechanoreceptor reflex reset the carotid baroreflex. Both carotid sinuses were vascularly isolated, and the carotid baroreceptors were stimulated with pulsatile pressure. Carotid baroreflex function curves were determined for aortic pressure, heart rate, and renal vascular conductance. Central command was evoked by electrical stimulation of the mesencephalic locomotor region (MLR) in cats that were paralyzed. The exercise pressor reflex was evoked by statically contracting the triceps surae muscles in cats that were not paralyzed. Likewise, the muscle mechanoreceptor reflex was evoked by stretching the calcaneal tendon in cats that were not paralyzed. We found that each of the three maneuvers shifted upward the linear relationship between carotid sinus pressure and aortic pressure and heart rate. Each of the maneuvers, however, had no effect on the slope of these baroreflex function curves. Our findings show that central command arising from the MLR as well as the exercise pressor reflex are capable of resetting the carotid baroreflex.
Angiotensin II stimulates cardiac L-type Ca2+current by a Ca2+- and protein kinase C-dependent mechanism
Authors: Aiello E. A. , Cingolani H. E.
Published: December 2017

Angiotensin II (ANG II) evokes positive inotropic responses in various species. However, the effects of this peptide on L-type Ca2+ currents ( I Ca) are still controversial. We report in this study that the effects of ANG II on I Ca differ depending on the mode of patch-clamp technique used, standard whole cell (WC) or perforated patch (PP). No significant effects of ANG II (0.5 μM) were observed when WC in cells dialyzed with high EGTA was used. However, when the intracellular milieu was preserved using PP, ANG II induced a significant 77 ± 6% increase in I Ca (−2.2 ± 0.3 in control and −3.9 ± 0.6 pA/pF in ANG II, n = 8, P < 0.05). When WC was used in cells dialyzed with low Ca2+ buffer capacity (EGTA 0.1 mM), ANG II was able to induce an increase in I Ca (−3.5 ± 0.3 in control vs. −4.8 ± 0.4 pA/pF in ANG II, n = 13, P < 0.05). This increase was prevented when the cells were also dialyzed with the protein kinase C (PKC) inhibitor chelerythrine (50 μM) or calphostin C (1 μM). The above results allow us to conclude that strong intracellular Ca2+buffering prevents the physiological actions of ANG II on cardiac I Ca, which are also dependent on activation of PKC.
Iodide and bromide inhibit Ca2+uptake by cardiac sarcoplasmic reticulum
Authors: Kargacin Gary J. , Ali Zenobia , Zhang Shi-Jin , Pollock Natashka S. , Kargacin Margaret E.
Published: December 2017

Recent studies indicate that the Ca2+permeability of the sarcoplasmic reticulum (SR) can be affected by its anionic environment. Additionally, anions could directly modulate the SR Ca2+pump or the movement of compensatory charge across the SR membrane during Ca2+uptake or release. To examine the effect of anion substitution on cardiac SR Ca2+uptake, fluorometric Ca2+measurements and spectrophotometric ATPase assays were used. Ca2+uptake into SR vesicles was inhibited in a concentration-dependent manner when Br−or I−replaced extravesicular Cl−(when Br−completely replaced Cl−, uptake velocity was ∼ 70% of control; when I−completely replaced Cl−, uptake velocity was ∼ 39% of control). Replacement of Cl−with SO[Formula: see text] had no effect on SR uptake. Although both I−and Br−inhibited net Ca2+uptake, neither anion directly inhibited the SR Ca2+pump nor did they increase the permeability of the SR membrane to Ca2+. Our results support the hypothesis that an anionic current that occurs during SR Ca2+uptake is reduced by the substitution of Br−or I−for Cl−.
Beneficial effects of adenosine A2aagonist CGS-21680 in infarcted and stunned porcine myocardium
Authors: Lasley Robert D. , Jahania M. Salik , Mentzer Robert M.
Published: December 2017

Although there are conflicting results on whether adenosine infusion during reperfusion alters infarct size, there are several reports that indicate adenosine A2aagonists reduce infarct size. There are also reports that the A2aagonist CGS-21680 increases cAMP and contractility in ventricular myocytes. The purpose of this study was to determine whether low-dose intracoronary infusions of CGS-21680 during reperfusion exert any beneficial effects in irreversibly and reversibly injured myocardium. Open-chest pigs were submitted to 60 min of coronary artery occlusion and 3 h of reperfusion. Treated pigs were administered intracoronary CGS-21680 (0.2 μg · kg−1· min−1) for the first 60 min of reperfusion. Pigs submitted to regional stunning (15 min ischemia) were treated with intracoronary CGS-21680 (0.15 μg · kg−1· min−1) after 2 h of reperfusion. In the infarct protocol, CGS-21680 reduced infarct size from 62 ± 2% of the region at risk to 36 ± 2%. In stunned myocardium, CGS increased load-independent regional preload recruitable stroke work and area by ≥70%, but the same infusion in normal myocardium was associated with no inotropic effect. Both beneficial effects were associated with little systemic hemodynamic effects. These findings suggest that reperfusion infusions of low doses of the A2aagonist CGS-21680 exert beneficial effects in reversibly and irreversibly injured myocardium.
Diabetes and hyperglycemia impair activation of mitochondrial KATP channels
Authors: Kersten Judy R. , Montgomery Matthew W. , Ghassemi Tannaz , Gross Eric R. , Toller Wolfgang G. , Pagel Paul S. , Warltier David C.
Published: December 2017

Hyperglycemia is an important predictor of cardiovascular mortality in patients with diabetes. We investigated the hypothesis that diabetes or acute hyperglycemia attenuates the reduction of myocardial infarct size produced by activation of mitochondrial ATP-regulated potassium (KATP) channels. Acutely instrumented barbiturate-anesthetized dogs were subjected to a 60-min period of coronary artery occlusion and 3 h of reperfusion. Myocardial infarct size (triphenyltetrazolium chloride staining) was 25 ± 1, 28 ± 3, and 25 ± 1% of the area at risk (AAR) for infarction in control, diabetic (3 wk after streptozotocin-alloxan), and hyperglycemic (15% intravenous dextrose) dogs, respectively. Diazoxide (2.5 mg/kg iv) significantly decreased infarct size (10 ± 1% of AAR, P < 0.05) but did not produce protection in the presence of diabetes (28 ± 5%) or moderate hyperglycemia (blood glucose 310 ± 10 mg/dl; 23 ± 2%). The dose of diazoxide and the degree of hyperglycemia were interactive. Profound (blood glucose 574 ± 23 mg/dl) but not moderate hyperglycemia blocked the effects of high-dose (5.0 mg/kg) diazoxide [26 ± 3, 15 ± 3 ( P < 0.05), and 11 ± 2% ( P < 0.05), respectively]. There were no differences in systemic hemodynamics, AAR, or coronary collateral blood flow (by radioactive microspheres) between groups. The results indicate that diabetes or hyperglycemia impairs activation of mitochondrial KATP channels.
TNF-α induces protein synthesis through PI3-kinase-Akt/PKB pathway in cardiac myocytes
Authors: Hiraoka Eiji , Kawashima Seinosuke , Takahashi Tomosaburo , Rikitake Yoshiyuki , Kitamura Tadahiro , Ogawa Wataru , Yokoyama Mitsuhiro
Published: December 2017

The activation of phosphatidylinositol (PI) 3-kinase and Akt/protein kinase B (PKB) by tumor necrosis factor (TNF)-α and their roles on stimulation of protein synthesis were investigated in cultured neonatal rat cardiac myocytes. Treatment of cells with TNF-α resulted in enlargement of cell surface area and stimulation of protein synthesis without affecting myocyte viability. TNF-α induced marked activation of PI3-kinase and Akt/PKB, and the activation of PI3-kinase and Akt/PKB was rapid (maximal at 10 and 15 min, respectively) and concentration dependent. Akt/PKB activation by TNF-α was inhibited by a PI3-kinase-specific inhibitor LY-294002 and adenovirus-mediated expression of a dominant negative mutant of PI3-kinase, indicating that TNF-α activates Akt/PKB through PI3-kinase activation. Furthermore, TNF-α-induced protein synthesis was inhibited by pretreatment with LY-294002 and expression of a dominant negative mutant of PI3-kinase or Akt/PKB. These results indicate that activation of the PI3-kinase-Akt/PKB pathway plays an essential role in protein synthesis induced by TNF-α in cardiac myocytes.
Parameters of red blood cell aggregation as correlates of the inflammatory state
Authors: Ami R. Ben , Barshtein G. , Zeltser D. , Goldberg Y. , Shapira I. , Roth A. , Keren G. , Miller H. , Prochorov V. , Eldor A. , Berliner S. , Yedgar S.
Published: December 2017

To identify clinically relevant parameters of red blood cell (RBC) aggregation, we examined correlations of aggregation parameters with C-reactive protein and fibrinogen in unstable angina (UA), acute myocardial infarction (AMI), and bacterial infection (BI). Aggregation parameters were derived from the distribution of RBC population into aggregate sizes (cells per aggregate) and changing of the distribution by flow-derived shear stress. Increased aggregation was observed in the following order: UA, AMI, and BI. The best correlation was obtained by integration of large aggregate fraction as a function of shear stress. To differentiate plasmatic from cellular factors in RBC aggregation, we determined the aggregation in the presence and absence of plasma and formulated a “plasma factor” (PF) ranging from 0 to 1. In AMI the enhanced aggregation was entirely due to PF (PF = 1), whereas in UA and BI it was due to both plasmatic and cellular factors (0 ≤ PF ≤ 1). It is proposed that clinically relevant parameters of RBC aggregation should express both RBC aggregate size distribution and aggregate resistance to disaggregation and distinguish between plasmatic and cellular factors.
Effects of luminal shear stress on cerebral arteries and arterioles
Authors: Bryan Robert M. , Marrelli Sean P. , Steenberg Marie L. , Schildmeyer Lisa A. , Johnson T. David
Published: December 2017

The effect of luminal shear stress was studied in cerebral arteries and arterioles. Middle cerebral arteries (MCA) and penetrating arterioles (PA) were isolated from male Long-Evans rats, mounted in a tissue bath, and pressurized. After the development of spontaneous tone, inside diameters were 186 ± 5 μm ( n = 28) for MCA and 65 ± 3 μm ( n = 37) for PA. MCA and PA constricted ∼20% with increasing flow. Flow-induced constriction persisted in MCA and PA after removal of the endothelium. After removal of the endothelium, the luminal application of a polypeptide containing the Arg-Gly-Asp amino acid sequence (inhibitor of integrin attachment) abolished the flow-induced constriction. Similarly, an antibody specific for the β3-chain of the integrin complex significantly inhibited the flow-induced constriction. The shear stress-induced constriction was accompanied by an increase in vascular smooth muscle Ca2+. For example, a shear stress of 20 dyn/cm2constricted MCA 8% ( n = 5) and increased Ca2+from 209 ± 17 to 262 ± 29 nM ( n = 5). We conclude that isolated cerebral arteries and arterioles from the rat constrict to increased shear stress. Because the endothelium is not necessary for the response, the shear forces must be transmitted across the endothelium, presumably by the cytoskeletal matrix, to elicit constriction. Integrins containing the β3-chain are involved with the shear stress-induced constrictions.
Phenylarsine oxide induces mitochondrial permeability transition, hypercontracture, and cardiac cell death
Authors: Korge Paavo , Goldhaber Joshua I. , Weiss James N.
Published: December 2017

The mitochondrial permeability transition (MPT) is implicated in cardiac reperfusion/reoxygenation injury. In isolated ventricular myocytes, the sulfhydryl (SH) group modifier and MPT inducer phenylarsine oxide (PAO) caused MPT, severe hypercontracture, and irreversible membrane injury associated with increased cytoplasmic free [Ca2+]. Removal of extracellular Ca2+or depletion of nonmitochondrial Ca2+pools did not prevent these effects, whereas the MPT inhibitor cyclosporin A was partially protective and the SH-reducing agent dithiothreitol fully protective. In permeabilized myocytes, PAO caused hypercontracture at much lower free [Ca2+] than in its absence. Thus PAO induced hypercontracture by both increasing myofibrillar Ca2+sensitivity and promoting mitochondrial Ca2+efflux during MPT. Hypercontracture did not directly cause irreversible membrane injury because lactate dehydrogenase (LDH) release was not prevented by abolishing hypercontracture with 2,3-butanedione monoxime. However, loading myocytes with the membrane-permeable Ca2+chelator 1,2-bis(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) prevented PAO-induced LDH release, thus implicating the PAO-induced rise in cytoplasmic [Ca2+] as obligatory for irreversible membrane injury. In conclusion, PAO induces MPT and enhanced susceptibility to hypercontracture in isolated cardiac myocytes, both key features also implicated in cardiac reperfusion and reoxygenation injury.
Effects of VEGF165and VEGF121on vasculogenesis and angiogenesis in cultured embryonic quail hearts
Authors: Yue Xinping , Tomanek Robert J.
Published: December 2017

It has been documented that hypoxia enhances coronary vasculogenesis and angiogenesis in cultured embryonic quail hearts via the upregulation of vascular endothelial growth factor (VEGF). In this study, we compared the functions of two VEGF splice variants. Ventricles from 6-day-old embryonic quail hearts were cultured on three-dimensional collagen gels. Recombinant human VEGF121or VEGF165were added to the culture medium for 48 h, and vascular growth was visualized by immunostaining with a quail-specific endothelial cell (EC) marker, QH1. VEGF165enhanced vascular growth in a dose-dependent manner: 5 ng/ml of VEGF165slightly increased the number of ECs, 10 ng/ml of VEGF165increased the incorporation of ECs into tubular structures, and at 20 ng/ml of VEGF165wider tubes were formed. This pattern plateaued at the 50 ng/ml dose. In contrast, VEGF121did not enhance either the number of ECs or tube formation at these or higher dosages. Combined effects of hypoxia and exogenous VEGF165were then compared. Tube formation from the heart explants treated with both hypoxia and 50 ng/ml of VEGF165had a morphology intermediate to those treated with hypoxia or VEGF165alone. Immunocytochemistry study revealed EC lumenization under all culture conditions. However, the addition of VEGF165stimulated the coalescence of ECs to form larger vessels. We conclude the following: 1) VEGF121and VEGF165induced by hypoxia have different functions on coronary vascular growth, 2) unknown factors induced by hypoxia can modify the effect of VEGF165, and 3) EC lumenization observed in the heart explant culture closely mimics in vivo coronary vasculogenesis.
Endothelial function during stimulation of renin-angiotensin system by low-sodium diet in humans
Authors: Omland Torbjørn , Johnson Wendy , Gordon Mary Beth , Creager Mark A.
Published: December 2017

We examined whether physiological stimulation of the endogenous renin-angiotensin system results in impaired endothelium-dependent vasodilatation in forearm resistance vessels of healthy subjects and whether this impairment can be prevented by angiotensin II type 1 receptor blockade. A low-sodium diet was administered to 27 volunteers who were randomized to concomitant treatment with losartan (100 mg once daily) or matched placebo in a double-blind fashion. Forearm blood flow was assessed by venous occlusion plethysmography at baseline and after 5 days. Endothelium-dependent and -independent vasodilation was assessed by intra-arterial infusion of methacholine and verapamil, respectively. The low-sodium diet resulted in significantly decreased urine sodium excretion (placebo: 146 ± 64 vs. 10 ± 9 meq/24 h, P < 0.001; losartan: 141 ± 56 vs. 14 ± 14 meq/24 h, P < 0.001) and increased plasma renin activity (placebo: 1.0 ± 0.5 vs. 5.0 ± 2.5 ng · ml−1 · h−1, P < 0.001; losartan: 3.8 ± 7.2 vs. 19.1 ± 11.2 ng · ml−1 · h−1, P = 0.006) in both the losartan and placebo groups. With the baseline study as the reference, the diet intervention was not associated with any significant change in endothelium-dependent vasodilation to methacholine in either the placebo ( P = 0.74) or losartan ( P = 0.40) group. We conclude that short-term physiological stimulation of the renin-angiotensin system does not cause clinically significant endothelial dysfunction. Losartan did not influence endothelium-dependent vasodilation in humans with a stimulated renin-angiotensin system.
EDHF is not K+ but may be due to spread of current from the endothelium in guinea pig arterioles
Authors: Coleman H. A. , Tare Marianne , Parkington Helena C.
Published: December 2017

Endothelium-derived hyperpolarizing factor (EDHF)-attributed hyperpolarizations and relaxations were recorded simultaneously from submucosal arterioles of guinea pigs with the use of intracellular microelectrodes and a video-based system, respectively. Membrane currents were recorded from electrically short segments of arterioles under single-electrode voltage clamp. Substance P evoked an outward current with a current-voltage relationship that was well described by the Goldman-Hodgkin-Katz equation for a K+ current, consistent with the involvement of intermediate- and small-conductance Ca2+-activated K+ channels. 1-Ethyl-2-benzimidazolinone relaxed the arterioles and evoked hyperpolarizations that were blocked by charybdotoxin, but not by iberiotoxin. Application of K+induced depolarization under conditions in which EDHF evoked hyperpolarization. The Ba2+-sensitive component of the K+-induced current was inwardly rectifying, in contrast to the outwardly rectifying current evoked by substance P. EDHF-attributed hyperpolarizations in dye-identified smooth muscle cells were indistinguishable from those recorded from dye-identified endothelial cells in the same arterioles. These results provide evidence that EDHF is not K+ but may involve electrotonic spread of hyperpolarization from the endothelial cells to the smooth muscle cells.
Estimation of diastolic intraventricular pressure gradients by Doppler M-mode echocardiography
Authors: Greenberg Neil L. , Vandervoort Pieter M. , Firstenberg Michael S. , Garcia Mario J. , Thomas James D.
Published: December 2017

Previous studies have shown that small intraventricular pressure gradients (IVPG) are important for efficient filling of the left ventricle (LV) and as a sensitive marker for ischemia. Unfortunately, there has previously been no way of measuring these noninvasively, severely limiting their research and clinical utility. Color Doppler M-mode (CMM) echocardiography provides a spatiotemporal velocity distribution along the inflow tract throughout diastole, which we hypothesized would allow direct estimation of IVPG by using the Euler equation. Digital CMM images, obtained simultaneously with intracardiac pressure waveforms in six dogs, were processed by numerical differentiation for the Euler equation, then integrated to estimate IVPG and the total (left atrial to left ventricular apex) pressure drop. CMM-derived estimates agreed well with invasive measurements (IVPG: y = 0.87 x + 0.22, r = 0.96, P < 0.001, standard error of the estimate = 0.35 mmHg). Quantitative processing of CMM data allows accurate estimation of IVPG and tracking of changes induced by β-adrenergic stimulation. This novel approach provides unique information on LV filling dynamics in an entirely noninvasive way that has previously not been available for assessment of diastolic filling and function.
Evidence of involvement of GIRK1/GIRK4 in long-term desensitization of cardiac muscarinic K+channels
Authors: Shui Zhigang , Yamanushi Tomoko Takahashi , Boyett Mark R.
Published: December 2017

The cardiac M2muscarinic receptor/G protein/K+channel system was studied in neonatal rat atrial cells cultured with and without 10 μM carbachol (CCh) for 24 h. Channel activity in CCh-pretreated cells was substantially reduced as a result of long-term desensitization regardless of whether the channel was activated by ACh in cell-attached patches or GTP in inside-out patches. Channel activity in CCh-pretreated cells was also low when the receptor was bypassed and the G protein and channel were directly activated by [γ-S]GTP or both the receptor and G protein were bypassed and the channel was directly activated by trypsin. Finally, in CCh-pretreated cells, the whole cell K+current was low when the channel was activated via the independent adenosine receptor. This suggests that the channel is involved in long-term desensitization. However, in CCh-pretreated cells, although the receptor was internalized, there was no internalization of the channel. We suggest that the function of the muscarinic K+channel declines in long-term desensitization of the cardiac M2muscarinic receptor/G protein/K+channel system.
Vasopressin-stimulated Ca2+spiking in vascular smooth muscle cells involves phospholipase D
Authors: Li Yanxia , Shiels Aaron J. , Maszak Gary , Byron Kenneth L.
Published: December 2017

Physiological concentrations of [Arg8]vasopressin (AVP; 10–500 pM) stimulate oscillations of cytosolic free Ca2+concentration (Ca2+spikes) in A7r5 vascular smooth muscle cells. We previously reported that this effect of AVP was blocked by a putative phospholipase A2(PLA2) inhibitor, ONO-RS-082 (5 μM). In the present study, the products of PLA2, arachidonic acid (AA), and lysophospholipids were found to be ineffective in stimulating Ca2+spiking, and inhibitors of AA metabolism did not prevent AVP-stimulated Ca2+spiking. Thin layer chromatography was used to monitor the release of AA and phosphatidic acid (PA), which are the products of PLA2and phospholipase D (PLD), respectively. AVP (100 pM) stimulated both AA and PA formation, but only PA formation was inhibited by ONO-RS-082 (5 μM). Exogenous PLD (type VII; 2.5 U/ml) stimulated Ca2+spiking equivalent to the effect of 100 pM AVP. AVP stimulated transphosphatidylation of 1-butanol (a PLD-catalyzed reaction) but not 2-butanol, and 1-butanol (but not 2-butanol) completely prevented AVP-stimulated Ca2+spiking. Protein kinase C (PKC) inhibition, which completely prevents AVP-stimulated Ca2+spiking, did not inhibit AVP-stimulated phosphatidylbutanol formation. These results suggest that AVP-stimulated Ca2+spiking depends on activation of PLD rather than PLA2and that PKC activation may be downstream of PLD in the signaling cascade.
Capillary filtration coefficient is independent of number of perfused capillaries in cat skeletal muscle
Authors: Bentzer Peter , Kongstad Lis , Grände Per-Olof
Published: December 2017

The capillary filtration coefficient (CFC) is assumed to reflect both microvascular hydraulic conductivity and the number of perfused capillaries at a given moment (precapillary sphincter activity). Estimation of hydraulic conductivity in vivo with the CFC method has therefore been performed under conditions of unchanged vascular tone and metabolic influence. There are studies, however, that did not show any change in CFC after changes in vascular tone and metabolic influence, and these studies indicate that CFC may not be influenced by alteration in the number of perfused capillaries. The present study reexamined to what extent CFC in a pressure-controlled preparation depends on the vascular tone and number of perfused capillaries by analyzing how CFC is influenced by 1) vasoconstriction, 2) increase in metabolic influence by decrease in arterial blood pressure, and 3) occlusion of precapillary microvessels by arterial infusion of microspheres. CFC was calculated from the filtration rate induced by a fixed decrease in tissue pressure. Vascular tone was increased in two steps by norepinephrine ( n = 7) or angiotensin II ( n = 6), causing a blood flow reduction from 7.2 ± 0.8 to at most 2.7 ± 0.2 ml · min−1 · 100 g−1( P < 0.05). The decrease in arterial pressure reduced blood flow from 4.8 ± 0.4 to 1.40 ± 0.1 ml · min−1 · 100 g−1( n = 6). Vascular resistance increased to 990 ± 260% of control after the infusion of microspheres ( n= 6). CFC was not significantly altered from control after any of the experimental interventions. We conclude that CFC under these conditions is independent of the vascular tone and number of perfused capillaries and that variation in CFC reflects variation in microvascular hydraulic conductivity.
Nitric oxide decreases pacemaker activity in lymphatic vessels of guinea pig mesentery
Authors: von der Weid Pierre-Yves , Zhao Jun , Van Helden Dirk F.
Published: December 2017

Intracellular microelectrode recordings were used to determine whether nitric oxide (NO), affects the pacemaker events that initiate vasomotion in lymphatic vessels of the guinea pig mesentery. This pacemaker activity is recorded as spontaneous transient depolarizations (STDs) and is likely to arise through synchronized Ca2+release from intracellular stores. We show here that acetylcholine-induced endothelium-derived NO and exogenous NO released by sodium nitroprusside (SNP; 100 μM) and DEA-NONOate (500 μM) reduced the frequency and amplitude of STDs. This inhibition of STD frequency and amplitude was independent of the NO-induced hyperpolarization of the smooth muscle. The SNP-induced inhibition of STD frequency and amplitude was abolished during superfusion with the soluble guanylyl cyclase inhibitor ODQ (10 μM) and was diminished in the presence of cGMP and cAMP-dependent protein kinase inhibitors. The data are consistent with the hypothesis that NO inhibits vasomotion primarily by production of cGMP and activation of both cGMP- and cAMP-dependent protein kinases, which reduce the size and frequency of STDs, probably by acting on the underlying synchronized Ca2+release from intracellular stores.
Regional expression of endothelin-1, ANP, IGF-1, and LV wall stress in the infarcted rat heart
Authors: Loennechen Jan P. , Støylen Asbjørn , Beisvag Vidar , Wisløff Ulrik , Ellingsen Øyvind
Published: December 2017

We hypothesized that myocardial infarction induces regional and temporal differences in endothelin-1 (ET-1), atrial natriuretic peptide (ANP), and insulin-like growth factor-1 (IGF-1) gene expression that correlate with left ventricular (LV) wall stress. Echocardiography and LV pressure measurements were performed in coronary artery-ligated or sham-operated rats. Gene expression was measured by competitive RT-PCR in the infarct, border zone, and remote area and in regionally isolated cardiomyocytes. ET-1 and IGF-1 expression was highest in the infarcted myocardium, whereas ANP expression was highest in noninfarcted myocardium. For all genes, remote area expression was highest after 7 days. At 42 days, ANP maintained maximum expression, ET-1 decreased to 50% of peak levels, and IGF-1 was normalized. Cardiomyocyte expression followed the same pattern as in the myocardium except for a markedly lower IGF-1 expression. Diastolic wall stress was the best hemodynamic variable to predict ET-1 and ANP expression in the remote area. We conclude that ET-1, ANP, and IGF-1 are expressed in different patterns in the infarcted heart in relation to time, functional regions, cellular distribution, and mechanical load.