bluuebunny/crossref_metadata_2025 huggingface dataset:
AM reverses pressor response to ET-1 independently of NO in rat coronary circulation
Authors: Kinnunen Pietari , Piuhola Jarkko , Ruskoaho Heikki , Szokodi István
Published: December 2017

Endothelin-1 (ET-1) elicits a vasoconstrictor response via ETAreceptors, whereas simultaneous activation of ETBreceptors triggers the release of nitric oxide (NO), which may limit the constrictor effect of ET-1. Recently, stimulation of ETBreceptors has been shown to increase the secretion of adrenomedullin (AM), a newly identified vasorelaxing peptide. The present study was designed to see whether AM can oppose the vasoconstrictor response to ET-1. In the isolated perfused paced rat heart preparation, infusion of ET-1 at concentrations of 1 nmol/l for 30 min induced a significant coronary vasoconstriction, whereas it had no effect on perfusion pressure at a dose of 0.08 nmol/l. Nω-nitro-l-arginine methyl ester (l-NAME; 300 μmol/l), a potent inhibitor of NO synthase (NOS), did not change the perfusion pressure when added alone to the perfusion fluid but it unmasked the constrictor effect of ET-1 at both concentrations. In the presence of l-NAME, AM (0.03 to 1 nmol/l) markedly reversed the pressor response to ET-1 at both concentrations. Administration of AM (0.03 and 1 nmol/l) alone resulted in a dose-dependent decrease in perfusion pressure, which was not modified in the presence of l-NAME. In conclusion, the coronary vasoconstrictor response to ET-1 is markedly augmented in the presence of a NOS inhibitor. This constrictor response is substantially reversed by AM. Our results indicate that AM may serve as a paracrine modulator of ET-1-induced vasoconstriction independently of the NO pathway.
ANG II in median preoptic nucleus and pressor responses to CSF sodium and high sodium intake in SHR
Authors: Budzikowski Adam S. , Leenen Frans H. H.
Published: December 2017

Pressor responses to increases in cerebrospinal fluid (CSF) sodium in Wistar rats and to high salt intake in spontaneously hypertensive rats (SHR) involve both brain ouabainlike activity (“ouabain”) and the brain renin-angiotensin system (RAS). Because some of the effects of “ouabain” are mediated by the median preoptic nucleus (MnPO) and this nucleus contains all elements of the RAS, the present study assessed possible interactions of “ouabain” and ANG II in this nucleus. In conscious Wistar rats, injection of ANG II into the MnPO significantly increased mean arterial pressure (MAP) and heart rate (HR). This response was not affected by pretreatment with a subpressor dose of ouabain. MAP and HR increases by ouabain in the MnPO were significantly attenuated by MnPO pretreatment with losartan. In Wistar rats, losartan in the MnPO also abolished pressor and HR responses to intracerebroventricular 0.3 M NaCl and attenuated MAP and HR responses to intracerebroventricular ouabain. Five weeks of a high-salt diet in SHRs resulted in exacerbation of hypertension and increased responses to air-jet stress and intracerebroventricular guanabenz. Losartan injected into the MnPO reversed the salt-sensitive component of the hypertension and normalized the depressor response to guanabenz but did not change responses to air-jet stress. We conclude that in the MnPO, ANG II via AT1 receptors mediates cardiovascular responses to an acute increase in CSF sodium as well as the chronic pressor responses to high sodium intake in SHR.
Rat cardiac contractile dysfunction induced by Ca2+ overload: possible link to the proteolysis of α-fodrin
Authors: Tsuji Tsuyoshi , Ohga Yoshimi , Yoshikawa Yoshiro , Sakata Susumu , Abe Takehisa , Tabayashi Nobuoki , Kobayashi Shuichi , Kohzuki Hisaharu , Yoshida Ken-Ichi , Suga Hiroyuki , Kitamura Soichiro , Taniguchi Shigeki , Takaki Miyako
Published: December 2017

The aim of the present study was to examine the mechanisms of Ca2+ overload-induced contractile dysfunction in rat hearts independent of ischemia and acidosis. Experiments were performed on 30 excised cross-circulated rat heart preparations. After hearts were exposed to high Ca2+, there was a contractile failure associated with a parallel downward shift of the linear relation between myocardial O2 consumption per beat and systolic pressure-volume area (index of a total mechanical energy per beat) in left ventricles from all seven hearts that underwent the protocol. This result suggested a decrease in O2consumption for total Ca2+ handling in excitation-contraction coupling. In the hearts that underwent the high Ca2+ protocol and had contractile failure, we found marked proteolysis of a cytoskeleton protein, α-fodrin, whereas other proteins were unaffected. A calpain inhibitor suppressed the contractile failure by high Ca2+, the decrease in O2 consumption for total Ca2+ handling, and membrane α-fodrin degradation. We conclude that the exposure to high Ca2+ may induce contractile dysfunction possibly by suppressing total Ca2+ handling in excitation-contraction coupling and degradation of membrane α-fodrin via activation of calpain.
Inhibition of Na+/Ca2+ exchange by KB-R7943: transport mode selectivity and antiarrhythmic consequences
Authors: Elias Chadwick L. , Lukas Anton , Shurraw Sabin , Scott Jason , Omelchenko Alexander , Gross Gil J. , Hnatowich Mark , Hryshko Larry V.
Published: December 2017

The Na+/Ca2+ exchanger plays a prominent role in regulating intracellular Ca2+ levels in cardiac myocytes and can serve as both a Ca2+ influx and efflux pathway. A novel inhibitor, KB-R7943, has been reported to selectively inhibit the reverse mode (i.e. , Ca2+ entry) of Na+/Ca2+ exchange transport, although many aspects of its inhibitory properties remain controversial. We evaluated the inhibitory effects of KB-R7943 on Na+/Ca2+exchange currents using the giant excised patch-clamp technique. Membrane patches were obtained from Xenopus laevis oocytes expressing the cloned cardiac Na+/Ca2+exchanger NCX1.1, and outward, inward, and combined inward-outward currents were studied. KB-R7943 preferentially inhibited outward (i.e., reverse) Na+/Ca2+ exchange currents. The inhibitory mechanism consists of direct effects on the transport machinery of the exchanger, with additional influences on ionic regulatory properties. Competitive interactions between KB-R7943 and the transported ions were not observed. The antiarrhythmic effects of KB-R7943 were then evaluated in an ischemia-reperfusion model of cardiac injury in Langendorff-perfused whole rabbit hearts using electrocardiography and measurements of left ventricular pressure. When 3 μM KB-R7943 was applied for 10 min before a 30-min global ischemic period, ventricular arrhythmias (tachycardia and fibrillation) associated with both ischemia and reperfusion were almost completely suppressed. The observed electrophysiological profile of KB-R7943 and its protective effects on ischemia-reperfusion-induced ventricular arrhythmias support the notion of a prominent role of Ca2+ entry via reverse Na+/Ca2+ exchange in this process.
Myocardial cross-bridge kinetics in transition to failure in Dahl salt-sensitive rats
Authors: McCurdy Daniel T. , Palmer Bradley M. , Maughan David W. , LeWinter Martin M.
Published: December 2017

The role of altered cross-bridge kinetics during the transition from cardiac hypertrophy to failure is poorly defined. We examined this in Dahl salt-sensitive (DS) rats, which develop hypertrophy and failure when fed a high-salt diet (HS). DS rats fed a low-salt diet were controls. Serial echocardiography disclosed compensated hypertrophy at 6 wk of HS, followed by progressive dilatation and impaired function. Mechanical properties of skinned left ventricular papillary muscle strips were analyzed at 6 wk of HS and then during failure (12 wk HS) by applying small amplitude (0.125%) length perturbations over a range of calcium concentrations. No differences in isometric tension-calcium relations or cross-bridge cycling kinetics or mechanical function were found at 6 wk. In contrast, 12 wk HS strips exhibited increased calcium sensitivity of isometric tension, decreased frequency of minimal dynamic stiffness, and a decreased range of frequencies over which cross bridges produce work and power. Thus the transition from hypertrophy to heart failure in DS rats is characterized by major changes in cross-bridge cycling kinetics and mechanical performance.
Progesterone regulation of vascular thromboxane A2receptors in rhesus monkeys
Authors: Minshall Richard D. , Pavcnik Dusan , Halushka Perry V. , Hermsmeyer Kent
Published: December 2017

We hypothesized that progesterone regulates thromboxane A2 receptor (TxA2R) density in primate vascular muscle and that TxA2R density correlates with coronary reactivity in vivo and in vitro. Reactivity to serotonin + U-46619 was determined by angiography in surgically postmenopausal [ovariectomized (Ovx)] rhesus monkeys without progesterone replacement and after 2-wk progesterone treatment (1–2 ng/ml). In untreated Ovx animals, 100 μmol/l serotonin + 1 μmol/l U-46619 (syringe concentrations) provoked vasospasm-like constrictions in six of six monkeys; zero of six progesterone-treated monkeys developed vasospasms. Sustained Ca2+ responses in vascular muscle cells isolated from Ovx coronaries (208 ± 63% of basal 20 min after stimulation) treated with serotonin + U-46619 contrasted with transient Ca2+ responses (143 ± 18% of basal and decreasing 5 min after stimulation) in progesterone-treated monkeys. The maximum density of [1 S-(1 I,2 J(5 Z),3 I(1 E,3 R*),4 I)]-7-[3-(3-hydroxy-4-(4′-[125I]iodophenoxy)- 1-butenyl)-7-oxabicyclo[2.2.1]heptan-2-yl]-5-heptenoic acid ([125I]-BOP) binding was greater ( P< 0.01) in carotid arteries and aortic membranes from Ovx (109 ± 11 fmol/mg) compared with progesterone-treated (43 ± 15 fmol/mg) monkeys. TxA2R immunolabeling revealed greater coronary TxA2R labeling in Ovx compared with progesterone-treated monkeys. The results suggest that progesterone can decrease arterial TxA2R in Ovx monkeys.
Differential regulation of SR calcium transporters by thyroid hormone in rat atria and ventricles
Authors: Shenoy Rajesh , Klein Irwin , Ojamaa Kaie
Published: December 2017

Thyroid hormone exerts positive inotropic effects on the heart mediated in part by its regulation of calcium transporter proteins, including sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2), phospholamban (PLB), and Na+/Ca2+ exchanger (NCX). To further understand the potential cardiac chamber-specific effects of thyroid hormone action, we compared the triiodo-l-thyronine (T3) responsiveness of calcium transporter proteins in atrial versus ventricular tissues. Rats were rendered hypothyroid by ingestion of propylthiouracil, and a subgroup of animals was treated with T3 for 7 days (7 μg/day by constant infusion). Atrial and left ventricular (LV) tissue homogenates were analyzed for expression of SERCA2, PLB, and NCX proteins by Western blot analysis. SERCA2 protein significantly decreased by 50% in hypothyroid LV and was normalized by T3 treatment. In contrast, SERCA2 protein in atria was unaltered in the hypothyroid state. PLB protein expression significantly increased by 1.6- and 5-fold in the hypothyroid LV and atria, respectively, and returned to euthyroid levels with T3 treatment. Expression of NCX protein showed a greater response to T3 treatment in atria tissue than in ventricular tissue. Sarcoplasmic reticulum calcium cycling is determined in part by the ratio of SERCA2 to PLB. This ratio was sixfold higher in the atria compared with LV, suggesting that PLB may play a minor role in the regulation of SERCA2 function in normal atria. We conclude that calcium transporter proteins are responsive to thyroid hormone in a chamber-specific manner, with atria showing a greater change in protein content in response to T3. The differential effect on atria may account for the occurrence of atrial rather than ventricular arrhythmias in response to even mild degrees of thyrotoxicosis.
Plasmin-dependent and -independent effects of plasminogen activators and inhibitor-1 on ex vivo angiogenesis
Authors: Brodsky Sergey , Chen Jun , Lee Albert , Akassoglou Katerina , Norman Jill , Goligorsky Michael S.
Published: December 2017

Plasminogen activator (PA) inhibitor-1 (PAI-1) has been recognized as a surrogate marker of endothelial dysfunction in diseases associated with impaired angiogenesis, including atherosclerosis, diabetic vasculopathy, and nephropathy. To establish the necessary and sufficient components of the PA system [PAI-1, urokinase-type PA (uPA), or tissue-type PA (tPA), and plasminogen (Plg)] for angiogenesis, we examined angiogenic competence of vascular explant cultures obtained from mice deficient in PAI-1, tPA, uPA, and Plg. To gain insight into the requirement for different matrix-degrading systems during endothelial cell migration across plasmin-degradable basement membranes compared with profibrotic areas containing plasmin-nondegradable collagen, we contrasted vascular sprouting in collagen with Matrigel lattices. PAI-1−/−vessels showed an increased capillary sprouting in both collagen and Matrigel. Deficiency of uPA significantly reduced the rate of sprouting, whereas tPA−/−vessels showed a profound inhibition of capillary sprouting. The Plg−/−vessels failed to sprout, a defect that was restored not only by exogenous Plg, but also by the addition of PAs; a nonproteolytic effect of tPA was observed in Matrigel. Zymography revealed no differences in the activity of metalloproteinase (MMP)-2 and -9 in wild-type and PAI-1−/−vessels, but demonstrated reduced MMP-9 activity in all angiogenesis-deficient vessels. In summary, 1) PAI-1 by itself is a modest inhibitor of endothelial sprouting, 2) tPA and Plg are indispensable for angiogenesis in this model, 3) Plg is not the only substrate for PAs, and 4) the activity of MMP-9 is undetectable in explant cultures from tPA and Plg knockout mice.
Cardiac titin isoforms are coexpressed in the half-sarcomere and extend independently
Authors: Trombitás K. , Wu Y. , Labeit D. , Labeit S. , Granzier H.
Published: December 2017

Titin, the third myofilament type of cardiac muscle, contains a molecular spring segment that gives rise to passive forces in stretched myocardium and to restoring forces in shortened myocardium. We studied cardiac titin isoforms (N2B and N2BA) that contain length variants of the molecular spring segment. We investigated how coexpression of isoforms takes place at the level of the half-sarcomere, and whether coexpression affects the extensibility of the isoforms. Immunoelectron microscopy was used to study local coexpression of isoforms in a range of species. It was found that the cardiac sarcomere of large mammals coexpresses N2B and N2BA titin isoforms at the level of the half-sarcomere, and that when coexpressed, the isoforms act independently of one another. Coexpressing isoforms at varying ratios results in modulation of the passive mechanical behavior of the sarcomere without impacting other functions of titin and allows for adjustment of the diastolic properties of the myocardium.
Platelet-conditioned medium increases endothelial electrical resistance independently of cAMP/PKA and cGMP/PKG
Authors: Gainor Jonathan P. , Morton Christine A. , Roberts Jared T. , Vincent Peter A. , Minnear Fred L.
Published: December 2017

Platelets release a soluble factor into blood and conditioned medium (PCM) that decreases vascular endothelial permeability. The objective of this study was to determine the signal-transduction pathway that elicits this decrease in permeability. Permeability-decreasing activity of PCM was assessed by the real-time measurement of electrical resistance across cell monolayers derived from bovine pulmonary arteries and microvessels. Using a desensitization protocol with cAMP/protein kinase A (PKA)-enhancing agents and pharmacological inhibitors, we determined that the activity of PCM is independent of PKA and PKG. Genistein, an inhibitor of tyrosine kinases, prevented the increase in endothelial electrical resistance. Because lysophosphatidic acid (LPA) has been proposed to be responsible for this activity of PCM and is known to activate the Giprotein, inhibitors of the G protein pertussis toxin and of the associated phosphatidylinositol 3-kinase (PI3K) wortmannin were used. Pertussis toxin and wortmannin caused a 10- to 15-min delay in the characteristic rise in electrical resistance induced by PCM. Inhibition of phosphorylation of extracellular signal-regulated kinase with the mitogen-activated kinase kinase inhibitors PD-98059 and U-0126 did not prevent the activity of PCM. Similar findings with regard to the cAMP protocols and inhibition of Giand PI3K were obtained for 1-oleoyl-LPA. These results demonstrate that PCM increases endothelial electrical resistance in vitro via a novel, signal transduction pathway independent of cAMP/PKA and cGMP/PKG. Furthermore, PCM rapidly activates a signaling pathway involving tyrosine phosphorylation, the Giprotein, and PI3K.
Hyperglycemia reduces coronary collateral blood flow through a nitric oxide-mediated mechanism
Authors: Kersten Judy R. , Toller Wolfgang G. , Tessmer John P. , Pagel Paul S. , Warltier David C.
Published: December 2017

We tested the hypothesis that hyperglycemia alters retrograde coronary collateral blood flow by a nitric oxide-mediated mechanism in a canine Ameriod constrictor model of enhanced collateral development. Administration of 15% dextrose to increase blood glucose concentration to 400 or 600 mg/dl decreased retrograde blood flow through the left anterior descending coronary artery to 78 ± 9 and 82 ± 8% of baseline values, respectively. In contrast, saline or l-arginine (400 mg · kg−1 · h−1) had no effect on retrograde flow. Coronary hypoperfusion and 1 h of reperfusion decreased retrograde blood flow similarly in saline- orl-arginine-treated dogs (76 ± 11 and 89 ± 4% of baseline, respectively), but these decreases were more pronounced in hyperglycemic dogs (47 ± 10%). l-Arginine prevented decreases in retrograde coronary collateral blood flow during hyperglycemia (100 ± 5 and 95 ± 6% of baseline at blood glucose concentrations of 400 and 600 mg/dl, respectively) and after coronary hypoperfusion and reperfusion (84 ± 14%). The results suggest that hyperglycemia decreases retrograde coronary collateral blood flow by adversely affecting nitric oxide availability.
Stretch and quick release of rat cardiac trabeculae accelerates Ca2+waves and triggered propagated contractions
Authors: Wakayama Yuji , Miura Masahito , Sugai Yoshinao , Kagaya Yutaka , Watanabe Jun , ter Keurs Henk E. D. J. , Shirato Kunio
Published: December 2017

Rapid shortening of active cardiac muscle [quick release (QR)] dissociates Ca2+from myofilaments. We studied, using muscle stretches and QR, whether Ca2+dissociation affects triggered propagated contractions (TPCs) and Ca2+waves. The intracellular Ca2+concentration was measured by a SIT camera in right ventricular trabeculae dissected from rat hearts loaded with fura 2 salt, force was measured by a silicon strain gauge, and sarcomere length was measured by laser diffraction while a servomotor controlled muscle length. TPCs ( n = 27) were induced at 28°C by stimulus trains (7.5 s at 2.65 ± 0.13 Hz) at an extracellular Ca2+concentration ([Ca2+]o) = 2.0 mM or with 10 μM Gd3+at [Ca2+]o= 5.2 ± 0.73 mM. QR during twitch relaxation after a 10% stretch for 100–200 ms reduced both the time between the last stimulus and the peak TPC (PeakTPC) and the time between the last stimulus and peak Ca2+wave (PeakCW) and increased PeakTPCand PeakCW( n= 13) as well as the propagation velocity ( Vprop; n = 8). Active force during stretch also increased Vprop( r = 0.84, n = 12, P < 0.01), but Gd3+had no effect ( n = 5). These results suggest that Ca2+dissociation by QR during relaxation accelerates the initiation and propagation of Ca2+waves.
Role of renin-angiotensin-aldosterone system in salt-sensitive hypertension induced by sensory denervation
Authors: Huang Yan , Wang Donna H.
Published: December 2017

To define the role of the renin-angiotensin-aldosterone system in a novel salt-sensitive model, neonatal Wistar rats were given capsaicin (50 mg/kg sc) on the first and second days of life. After weaning, male rats were divided into the following six groups and treated for 3 wk with: control + normal sodium diet (CON-NS), CON + high-sodium diet (CON-HS), CON + HS + spironolactone (50 mg · kg−1· day−1, CON-HS-SP), capsaicin pretreatment + NS (CAP-NS), CAP-HS, and CAP-HS-SP. Radioimmunoassay shows that plasma renin activity (PRA) and plasma aldosterone level (PAL) were suppressed by HS, but they were higher in CAP-HS than in CON-HS and CON-HS-SP ( P < 0.05). Both tail-cuff systolic blood pressure and mean arterial pressure were higher in CAP-HS than in all other groups ( P < 0.05). Urine water and sodium excretion were increased with HS intake, but they were lower in CAP-HS than in CON-HS ( P < 0.05). Western blot did not detect differences in adrenal AT1receptor content. Therefore, insufficiently suppressed PRA and PAL in response to HS intake by sensory denervation may contribute to increased salt sensitivity and account for effectiveness of spironolactone in lowering blood pressure in this model.
DNA enzyme targeting TNF-α mRNA improves hemodynamic performance in rats with postinfarction heart failure
Authors: Iversen Per Ole , Nicolaysen Gunnar , Sioud Mouldy
Published: December 2017

Tumor necrosis factor-α (TNF-α) probably affects the pathogenesis of heart failure. Here we have investigated the therapeutic potential of a nuclease-resistant DNA enzyme that specifically cleaves TNF-α mRNA. A phosphorothioate-modified DNA enzyme was designed to retain similar cleavage activity as its unmodified version, and that inhibited the expression of TNF-α in vitro. To test its efficacy in vivo, postinfarction congestive heart failure was induced in anesthetized rats by ligation of the left coronary artery. A 4-wk treatment with the DNA enzyme induced a substantial reduction in left ventricular end-diastolic pressure and lung weight concomitant with an increase in arterial blood pressure and myocardial blood flow compared with controls. The concentration of TNF-α in coronary sinus blood was markedly lowered on treatment, and myocardial TNF-α mRNA was substantially reduced. Recovery studies showed that the DNA enzyme cleavage activity was present within the myocardium throughout the observation period and had no apparent toxic effects. Our findings indicate that DNA enzyme-based therapy may hold promise in the treatment of this debilitating disease.
Blocking Na+/H+exchange reduces [Na+]iand [Ca2+]iload after ischemia and improves function in intact hearts
Authors: An Jianzhong , Varadarajan Srinivasan G. , Camara Amadou , Chen Qun , Novalija Enis , Gross Garrett J. , Stowe David F.
Published: December 2017

We determined in intact hearts whether inhibition of Na+/H+exchange (NHE) decreases intracellular Na+and Ca2+during ischemia and reperfusion, improves function during reperfusion, and reduces infarct size. Guinea pig isolated hearts were perfused with Krebs-Ringer solution at 37°C. Left ventricular (LV) free wall intracellular Na+concentration ([Na+]i) and intracellular Ca2+concentration ([Ca2+]i) were measured using fluorescence dyes. Hearts were exposed to 30 min of ischemia with or without 10 μM of benzamide (BIIB-513), a selective NHE-1 inhibitor, infused for 10 min just before ischemia or for 10 min immediately on reperfusion. At 2 min of reperfusion, BIIB-513 given before ischemia decreased peak increases in [Na+]iand [Ca2+]i, respectively, from 2.5 and 2.3 times (controls) to 1.6 and 1.3 times preischemia values. At 30 min of reperfusion, BIIB-513 increased systolic-diastolic LV pressure (LVP) from 49 ± 2% (controls) to 80 ± 2% of preischemia values. BIIB-513 reduced ventricular fibrillation by 54% and reduced infarct size from 64 ± 1% to 20 ± 3%. First derivative of the LVP, O2consumption, and cardiac efficiency were also improved by BIIB-513. Similar results were obtained with BIIB-513 given on reperfusion. These data show that Na+loading is a marker of reperfusion injury in intact hearts in that inhibiting NHE reduces Na+and Ca2+loading during reperfusion while improving function. These results clearly implicate the ionic basis by which inhibiting NHE protects the guinea pig intact heart from ischemia-reperfusion injury.
Enhanced PKCβII translocation and PKCβII-RACK1 interactions in PKCε-induced heart failure: a role for RACK1
Authors: Pass Jason M. , Gao Jiuming , Jones W. Keith , Wead William B. , Wu Xin , Zhang Jun , Baines Christopher P. , Bolli Roberto , Zheng Yu-Ting , Joshua Irving G. , Ping Peipei
Published: December 2017

Recent investigations have established a role for the βII-isoform of protein kinase C (PKCβII) in the induction of cardiac hypertrophy and failure. Although receptors for activated C kinase (RACKs) have been shown to direct PKC signal transduction, the mechanism through which RACK1, a selective PKCβII RACK, participates in PKCβII-mediated cardiac hypertrophy and failure remains undefined. We have previously reported that PKCε activation modulates the expression of RACKs, and that altered ε-isoform of PKC (PKCε)-RACK interactions may facilitate the genesis of cardiac phenotypes in mice. Here, we present evidence that high levels of PKCε activity are commensurate with impaired left ventricular function (dP/d t = 6,074 ± 248 mmHg/s in control vs. 3,784 ± 269 mmHg/s in transgenic) and significant myocardial hypertrophy. More importantly, we demonstrate that high levels of PKCε activation induce a significant colocalization of PKCβII with RACK1 (154 ± 7% of control) and a marked redistribution of PKCβII to the particulate fraction (17 ± 2% of total PKCβII in control mice vs. 49 ± 5% of total PKCβII in hypertrophied mice), without compensatory changes of the other eight PKC isoforms present in the mouse heart. This enhanced PKCβII activation is coupled with increased RACK1 expression and PKCβII-RACK1 interactions, demonstrating PKCε-induced PKCβII signaling via a RACK1-dependent mechanism. Taken together with our previous findings regarding enhanced RACK1 expression and PKCε-RACK1 interactions in the setting of cardiac hypertrophy and failure, these results suggest that RACK1 serves as a nexus for at least two isoforms of PKC, the ε-isoform and the βII-isoform, thus coordinating PKC-mediated hypertrophic signaling.
Endothelin antagonist reduces hemodynamic responses to vasopressin in DOCA-salt hypertension
Authors: Yu Ming , Gopalakrishnan Venkat , Wilson Thomas W. , McNeill J. Robert
Published: December 2017

The contribution of endothelin to the changes in blood pressure, cardiac output, and total peripheral resistance evoked by arginine vasopressin and angiotensin II was investigated in deoxycorticosterone acetate (DOCA)-salt hypertensive rats by infusing the peptides intravenously before and after pretreatment with the endothelin receptor antagonist bosentan. Blood pressure was recorded with radiotelemetry devices and cardiac output was recorded with ultrasonic transit time flow probes in conscious unrestrained animals. The dose-related decreases in cardiac output induced by vasopressin and angiotensin II were unaffected by bosentan. In contrast, the dose-related increases in total peripheral resistance evoked by vasopressin were blunted in both DOCA-salt hypertensive and sham normotensive rats, but this effect of bosentan was greater in the DOCA-salt hypertensive group. In contrast with vasopressin, bosentan failed to change hemodynamic responses to angiotensin II. The exaggerated vascular responsiveness (total peripheral resistance) of the DOCA-salt hypertensive group to vasopressin was largely abolished by bosentan. These results suggest that endothelin contributes to the hemodynamic effects of vasopressin but not angiotensin II in the DOCA-salt model of hypertension.
Arteriogenesis and angiogenesis in rat ischemic hindlimb: role of nitric oxide
Authors: Lloyd Pamela G. , Yang Hsiao T. , Terjung Ronald L.
Published: December 2017

Nitric oxide (NO) has been implicated in both collateral expansion (arteriogenesis) and capillary growth (angiogenesis). Exercise training increases collateral-dependent blood flow to tissues at risk of ischemia and enhances capillarity in active skeletal muscle. Exercise also acutely elevates NO. Thus we assessed the role of NO in training-induced arteriogenesis and angiogenesis. These studies utilized a rat model of peripheral vascular disease (bilateral femoral artery ligation). Untreated rats (control) and rats treated with the NO synthase inhibitor N ω-nitro-l-arginine methyl ester (l-NAME; 65–70 mg · kg−1 · day−1, via drinking water) were divided into sedentary or exercise-trained subgroups. After ∼3 wk, l-NAME treatment had elevated preexercise mean arterial pressure ∼39–58%, confirming NO synthesis inhibition. The training program (treadmill exercise twice per day, 20–25 m/min, 15% grade, ∼18 days) increased collateral-dependent blood flow to the distal hindlimb, with the greatest increase (∼59%) in the calf ( P < 0.001). This increase was inhibited by l-NAME. In contrast, the training-induced increase in muscle capillarity was not blocked byl-NAME. Thus arteriogenesis and angiogenesis appear to differ in their requirement for NO.
Attenuation of oxidant stress during reoxygenation by AMP 579 in cardiomyocytes
Authors: Xu Zhelong , Cohen Michael V. , Downey James M. , Vanden Hoek Terry L. , Yao Zhenhai
Published: December 2017

AMP 579, an adenosine A1/A2receptor agonist, has a strong anti-infarct effect when administered just before reperfusion. Because oxidative stress has been proposed to contribute to myocardial reperfusion injury, we tested whether AMP 579 can reduce the production of reactive oxidant species (ROS) during reoxygenation in cultured chick embryonic cardiomyocytes. The intracellular fluorescent probe 2′,7′-dichlorofluorescin diacetate (DCFH) was used to detect ROS. The cells were subjected to 60 min of simulated ischemia, followed by either 15 min or 3 h of reoxygenation. AMP 579 (0.5 and 1 μM), when started 10 min before reoxygenation, significantly reduced ROS generation from 4.86 ± 0.30 (arbitrary units) in untreated cells to 2.72 ± 0.31 and 1.85 ± 0.14, respectively ( P < 0.05). Cell death that was assessed by propidium iodide uptake was markedly reduced by AMP 579 (49.6 ± 4.7% of control cells vs. 25.4 ± 2.4%, P < 0.05). In contrast, adenosine did not alter ROS generation or cell death. Attenuation of ROS production by AMP 579 was completely prevented by simultaneous exposure of cells to the selective adenosine A2antagonist 8-(13-chlorostyryl) caffeine. These results indicate that AMP 579 directly protects cardiomyocytes from reperfusion injury by a mechanism that attenuates intracellular oxidant stress. Furthermore, adenosine could not duplicate these effects.
AT2 receptor-mediated vasodilation in the heart: effect of myocardial infarction
Authors: Schuijt Martin P. , Basdew Munesh , van Veghel Richard , de Vries René , Saxena Pramod R. , Schoemaker Regien G. , Jan Danser A. H.
Published: December 2017

To investigate the functional consequences of postinfarct cardiac angiotensin (ANG) type 2 (AT2) receptor upregulation, rats underwent coronary artery ligation or sham operation and were infused with ANG II 3–4 wk later, when scar formation is complete. ANG II increased mean arterial pressure (MAP) more modestly in infarcted animals than in sham animals. The AT1 receptor antagonist irbesartan, but not the AT2 receptor antagonist PD123319, decreased MAP and antagonized the ANG II-mediated systemic hemodynamic effects. Myocardial (MVC) but not renal vascular conductance (RVC) was diminished in infarcted versus sham rats. ANG II did not affect MVC and reduced RVC in all rats. MVC was unaffected by irbesartan and PD123319 in all animals. However, with PD123319, ANG II reduced MVC in sham but not infarcted animals, and, with irbesartan, ANG II increased MVC in infarcted but not sham animals. Irbesartan increased RVC and antagonized the ANG II-mediated renal effects in all animals. RVC, at baseline or with ANG II, was not affected by PD123319 in infarcted and sham animals. In conclusion, coronary but not renal AT2 receptor stimulation results in vasodilation, and this effect is enhanced in infarcted rats.
Endothelial NOS-dependent activation of c-Jun NH2- terminal kinase by oxidized low-density lipoprotein
Authors: Go Young-Mi , Levonen Anna-Liisa , Moellering Douglas , Ramachandran Anup , Patel Rakesh P. , Jo Hanjoong , Darley-Usmar Victor M.
Published: December 2017

Oxidized low-density lipoprotein (oxLDL) is known to activate a number of signal transduction pathways in endothelial cells. Among these are the c-Jun NH2-terminal kinase (JNK), also known as stress-activated protein kinase, and extracellular signal-regulated kinase (ERK). These mitogen-activated protein kinases (MAP kinase) determine cell survival in response to environmental stress. Interestingly, JNK signaling involves redox-sensitive mechanisms and is activated by reactive oxygen and nitrogen species derived from both NADPH oxidases, nitric oxide synthases (NOS), peroxides, and oxidized low-density lipoprotein (oxLDL). The role of endothelial NOS (eNOS) in the activation of JNK in response to oxLDL has not been examined. Herein, we show that on exposure of endothelial cells to oxLDL, both ERK and JNK are activated through independent signal transduction pathways. A key role of eNOS activation through a phosphatidylinositol-3-kinase-dependent mechanism leading to phosphorylation of eNOS is demonstrated for oxLDL-dependent activation of JNK. Moreover, we show that activation of ERK by oxLDL is critical in protection against the cytotoxicity of oxLDL.
A forward model-based validation of cardiovascular system identification
Authors: Mukkamala Ramakrishna , Cohen Richard J.
Published: December 2017

We present a theoretical evaluation of a cardiovascular system identification method that we previously developed for the analysis of beat-to-beat fluctuations in noninvasively measured heart rate, arterial blood pressure, and instantaneous lung volume. The method provides a dynamical characterization of the important autonomic and mechanical mechanisms responsible for coupling the fluctuations (inverse modeling). To carry out the evaluation, we developed a computational model of the cardiovascular system capable of generating realistic beat-to-beat variability (forward modeling). We applied the method to data generated from the forward model and compared the resulting estimated dynamics with the actual dynamics of the forward model, which were either precisely known or easily determined. We found that the estimated dynamics corresponded to the actual dynamics and that this correspondence was robust to forward model uncertainty. We also demonstrated the sensitivity of the method in detecting small changes in parameters characterizing autonomic function in the forward model. These results provide confidence in the performance of the cardiovascular system identification method when applied to experimental data.
Pulmonary arterial morphometry from microfocal X-ray computed tomography
Authors: Karau Kelly L. , Molthen Robert C. , Dhyani Anita , Haworth Steven T. , Hanger Christopher C. , Roerig David L. , Johnson Roger H. , Dawson Christopher A.
Published: December 2017

The objective of this study was to develop an X-ray computed tomographic method for pulmonary arterial morphometry. The lungs were removed from a rat, and the pulmonary arterial tree was filled with perfluorooctyl bromide to enhance X-ray absorbance. At each of four pulmonary arterial pressures (30, 21, 12, and 5.4 mmHg), the lungs were rotated within the cone of the X-ray beam that was projected from a microfocal X-ray source onto an image intensifier, and 360 images were obtained at 1° increments. The three-dimensional image volumes were reconstructed with isotropic resolution with the use of a cone beam reconstruction algorithm. The luminal diameter and distance from the inlet artery were measured for the main trunk, its immediate branches, and several minor trunks. These data revealed a self-consistent tree structure wherein the portion of the tree downstream from any vessel of a given diameter has a similar structure. Self-consistency allows the entire tree structure to be characterized by measuring the dimensions of only the vessels comprising the main trunk of the tree and its immediate branches. An approach for taking advantage of this property to parameterize the morphometry and distensibility of the pulmonary arterial tree is developed.
Force-velocity relationship of myogenically active arterioles
Authors: Davis Michael J. , Davidson Judy
Published: December 2017

We compared the shortening velocity of smooth muscle in arterioles that had low or high levels of myogenic tone or norepinephrine (NE)-induced tone. We hypothesized that enhanced myogenic tone of arterioles reflects an enhanced maximum velocity of shortening of arteriolar smooth muscle in a way that is different from that produced by NE. These concepts are untested assumptions of arteriolar mechanics. Second-order arterioles from hamster cheek pouch (passive diameter at 40 mmHg = 42 μm) were isolated and cannulated for in vitro study. In the absence of flow, pressure was controlled by hydraulic pumps so that servo control of wall tension could be achieved from measurement of internal diameter and pressure. Isotonic quick-release protocols were used to measure the initial velocity of shortening following release from control wall tension (afterload) to a series of fractional afterloads. After release, the initial rates of shortening were fit to the Hill equation to obtain coefficients for a hyperbolic fit of the velocity-afterload relationship. The maximal unloaded shortening velocity for partially activated arterioles ( V′max) was determined from the y-intercept of each plot. Using this procedure, we compared V′max from two groups of arterioles equilibrated at low or high pressure, i.e., with low or high myogenic tone. Arterioles with higher myogenic tone had higher values of V′max than arterioles with lower myogenic tone. V′max for arterioles partially activated with NE at low pressure was comparable to V′max for arterioles with high myogenic tone, but NE produced high velocities at low force, whereas enhanced myogenic tone produced roughly parallel shifts in velocity and force. The results suggest that increased myogenic tone does indeed reflect enhanced activation of arteriolar smooth muscle, and this effect is mechanically different from that produced by NE.
Regional prolongation of ARI and altered restitution properties cause ventricular arrhythmia in heart failure
Authors: Watanabe Tetsu , Yamaki Michiyasu , Yamauchi Sou , Minamihaba Osamu , Miyashita Takehiko , Kubota Isao , Tomoike Hitonobu
Published: December 2017

The mechanism of arrhythmogenicity in heart failure remains poorly understood. We examined the relationship between electrical abnormalities and ventricular arrhythmia by using experimental heart failure models. Sixty unipolar electrograms were recorded from the entire cardiac surface in control dogs ( n = 13) and pacing-induced heart failure dogs ( n = 16). In failing hearts, activation time (AT) was delayed at the apex, and AT dispersion increased in failing hearts. Activation-recovery intervals (ARI) were prolonged mainly at the apex and ARI dispersion was significantly augmented. The slope of the ARI restitution curve, interaction of diastolic interval, and ARI in failing hearts was significantly steeper than in control hearts. Ventricular fibrillation (VF) was easily induced by programmed stimulation in failing hearts, whereas no arrhythmia occurred in control hearts. Computer simulation studies could reproduce the experimental results. Altering the ARI restitution to the steep slope causes VF in a model heart. It is suggested that electrical remodeling, especially steepness of electrical restitution, may play a role in arrhythmogenicity in failing hearts.
Pulsation-induced dilation of subendocardial and subepicardial arterioles: effect on vasodilator sensitivity
Authors: Sorop Oana , Spaan Jos A. E. , VanBavel Ed
Published: December 2017

Coronary vessels are squeezed by the surrounding myocardium during systole, impeding blood flow specifically in the subendocardium. To study the myocardial compression effect, we applied pulsatile transvascular pressure to isolated, cannulated subendocardial (Endo) and subepicardial (Epi) resistance arteries. Pressure pulsation at 0.5 to 2.5 Hz between 20 and 100 mmHg induced dilation of preconstricted vessels that was somewhat larger in Epi arterioles. In four Epi and five Endo arterioles loaded with fura 2, pulsation led to a small increase in intracellular calcium. Pulsation induced a significant decrease in IC50for bradykinin (BK) (5.9 ± 0.6 vs. 27.3 ± 3.2 nM in Epi vessels and 7.6 ± 0.3 vs. 302 ± 9 nM in Endo vessels), compared with steady pressure. The adenosine (Ado) sensitivity was not significantly affected (2.21 ± 0.08 vs. 3.76 ± 0.4 μM) in Epi arteries but was enhanced during pulsations in Endo vessels (3.1 ± 0.3 vs. 10.1 ± 0.6 μM). When pulsation-induced dilation was compensated by a higher concentration of the preconstrictor (U-46619), a significantly larger dilation to BK or Ado was found during pulsations. In conclusion, pulsation-induced dilation occurs at physiologically relevant frequencies and amplitudes in Endo vessels. The process does not involve intracellular calcium reduction and increases vasodilator sensitivity.
Protein kinase C-ζ modulates thromboxane A2-mediated apoptosis in adult ventricular myocytes via Akt
Authors: Shizukuda Yukitaka , Buttrick Peter M.
Published: December 2017

We hypothesized that thromboxane A2(TxA2) receptor stimulation directly induces apoptosis in adult cardiac myocytes. To investigate this, we exposed cultured adult rat ventricular myocytes (ARVM) to a TxA2mimetic [1S-[1α,2α(Z),3β(1E,3S*),4α]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (I-BOP) for 24 h. Stimulation with I-BOP induced apoptosis in a dose-dependent manner and was completely prevented by a TxA2receptor antagonist, SQ-29548. We further investigated the role of protein kinase C (PKC) in this process. TxA2stimulation resulted in membrane translocation of PKC-ζ but not PKC-α, -βII, -δ, and -ε at 3 min and 1 h. The activation of PKC-ζ by I-BOP was confirmed using an immune complex kinase assay. Treatment of ARVM with a cell-permeable PKC-ζ pseudosubstrate peptide (ζ-PS) significantly attenuated apoptosis by I-BOP. In addition, I-BOP treatment decreased baseline Akt activity and its decrease was reversed by treatment with ζ-PS. The inhibition of phosphatidylinositol 3-kinase upstream of Akt by wortmannin or LY-294002 abolished the antiapoptotic effect of ζ-PS. Therefore, our results suggest that the activation of PKC-ζ modulates TxA2receptor-mediated apoptosis at least, in part, through Akt activity in adult cardiac myocytes.
Glycyrrhetinic derivatives inhibit hyperpolarization in endothelial cells of guinea pig and rat arteries
Authors: Tare Marianne , Coleman H. A. , Parkington Helena C.
Published: December 2017

Glycyrrhetinic acid (GA) derivatives have been used to implicate gap junctions in vasorelaxation attributed to endothelium-derived hyperpolarizing factor (EDHF). The aim of this study was to assess whether GA compounds affect endothelial cell hyperpolarization. Membrane potentials were recorded from dye-identified endothelial and smooth muscle cells of guinea pig coronary and rat mesenteric arteries. GA derivatives had varied effects on the resting membrane potential: depolarization, hyperpolarization, or no effect, depending on the artery. 18α-GA (50 μM) had a small variable effect on ACh-induced hyperpolarizations in endothelial cells. 18β-GA (30 μM) and carbenoxolone (100 μM) significantly reduced ACh-induced hyperpolarizations in both endothelial and smooth muscle cells. Smooth muscle action potentials in rat tail arteries were smaller and slower in the presence of 18β-GA. Nerve-induced excitatory junction potentials were inhibited by 18β-GA and carbenoxolone, whereas the time course of their decay initially increased and then decreased. In conclusion, the GA compounds had a range of effects. Their inhibition of the EDHF hyperpolarization and relaxation in the smooth muscle may stem from the inhibition of endothelial cell hyperpolarization.
Brachial artery dilatation responses in healthy children and adolescents
Authors: Järvisalo Mikko J. , Rönnemaa Tapani , Volanen Iina , Kaitosaari Tuuli , Kallio Katariina , Hartiala Jaakko J. , Irjala Kerttu , Viikari Jorma S. A. , Simell Olli , Raitakari Olli T.
Published: December 2017

To characterize brachial artery flow-mediated dilatation (FMD) in children, we monitored arterial diameter changes with ultrasound between 40 and 180 s after a 4.5-min forearm cuff occlusion-induced hyperemia in 105 healthy children (mean age, 11 yr; range, 9–16 yr). The peak FMD was 7.7 ± 4.0% and occurred 79 ± 33 s after cuff release. FMD at 60 s (5.3 ± 4.0%) was significantly lower than the peak FMD ( P < 0.0001). Twenty-three percent of the children ( n = 24) reached peak FMD first after 110 s of postocclusion. Compared with others, these late responders weighed less, had smaller vessel size, and were more often girls, but had similar peak FMD. In multivariate analysis, FMD responses were inversely associated with brachial artery baseline diameter and serum cholesterol concentration. We conclude that the time to reach the peak FMD response in children varies considerably. When studying endothelial function in children with the use of the noninvasive ultrasound method, several brachial artery diameter measurements up to 120 s after cuff release are needed to determine the true FMD peak response.
Affinity of cartilage matrix for calcium
Authors: Thomas William C. , Pickett Wilbur C.
Published: December 2017

Cartilage matrix from rachitic rats mineralizes in vitro on incubation in appropriate solutions and, if the phosphorus concentration is constant, the degree of mineralization varies directly witd concentrations of calcium between 3.5 and 6.0 mg/100 ml. On adding to a standard incubating solution various organic or amino acids known to form chelates with calcium it was found that inhibition of matrix mineralization varied directly with the chelating propensity of these acids. These observations indicate that mineralizable cartilage matrix does not have an affinity for calcium exceeding that of any chelating agent tested. Moreover, as cartilage apparently requires calcium in a readily available, persumably ionic, form for mineralization, this tissue may be used as a means of determining the dissociation constants for calcium chelates. From the preliminary data obtained in this experiment dissociation constants were calculated for the following ligands: citrate, tartrate, malonate, succinate and glutamate. These derived values may be more appropriate to biological systems under simulated physiological conditions than are those determined by strictly chemical means.
Glycogenolytic effect of vasopressin in the canine liver
Authors: Bergen Stanley S. , Sullivan Robert , Hilton James G. , Willis S. Waring , Van Itallie Theodore B.
Published: December 2017

The effect of synthetic vasopressin and oxytocin upon glucose flux across the liver was studied in fasted, unanesthetized dogs. Blood samples were obtained before and after hormone administration from portal and hepatic veins and aorta by means of catheters chronically implanted in these vessels. Responses to commercial Pitressin and Pitocin also were measured. Immediately following intraportal administration of 5–60 u of vasopressin (or Pitressin) an appreciable increment of glucose appeared in the hepatic vein, reaching a peak at 10 minutes and returning to base line levels within 30 minutes. During this time, glucose concentration in the portal vein failed to increase and in some instances decreased. Administration of 10–40 u of oxytocin (or Pitocin) failed to induce any change in hepatic vein glucose concentration.