bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of ischemia on soluble and particulate guanylyl cyclase-mediated cGMP synthesis in cardiomyocytes
Authors: Agulló Luis , Garcia-Dorado David , Escalona Noelia , Ruiz-Meana Marisol , Inserte Javier , Soler-Soler Jordi
Published: March 2015

The effect of simulated ischemia [hypoxia, no glucose, extracellular pH (pHo) 6.4] on cGMP synthesis induced by stimulation of soluble (sGC) or particulate guanylyl cyclase (pGC) was investigated in adult rat cardiomyocytes. Intracellular cGMP content was measured after stimulation of sGC by S-nitroso- N-penicillamine (SNAP) or stimulation of pGC by natriuretic peptides [urodilatin (Uro), atrial natriuretic peptide (ANP), or C-type natriuretic peptide (CNP)] for 1 min in the presence of phosphodiesterase inhibitors. After 2 h of simulated ischemia, a decrease of >50% was observed in pGC-dependent cGMP synthesis, but no significant change was observed in sGC-dependent cGMP synthesis. The reduction in cGMP synthesis caused by simulated ischemia was mimicked by extracellular acidosis (pHo6.4), which decreased pGC-mediated cGMP synthesis without altering sGC-mediated cGMP synthesis. An extreme sensitivity of pGC activity to low pH was also observed in membrane cell fractions. Hypoxia without acidosis (pHo7.4) profoundly depressed cellular ATP content but did not change the response to SNAP, Uro, or ANP (selective agonists of pGC type A receptor). Only cGMP synthesis in response to CNP (a selective agonist of pGC type B receptor) was significantly reduced by ATP depletion. These data support the relevance of intracellular pH as a modulator of cGMP and suggest that, in ischemic cardiomyocytes, synthesis of cGMP would be mainly nitric oxide dependent.
Contribution of systemic vascular resistance and total arterial compliance to effective arterial elastance in humans
Authors: Chemla Denis , Antony Isabelle , Lecarpentier Yves , Nitenberg Alain
Published: March 2015

The respective contribution of systemic vascular resistance ( R) and total arterial compliance ( C) to the arterial load remains to be established in humans. Effective arterial elastance ( Ea), i.e., the left ventricular end-systolic pressure (LVESP)-over-stroke volume ratio, is a reliable estimate of arterial load. It is widely accepted that Ea mainly relates to mean aortic pressure (MAP) and thus to the R-to- T ratio ( R/ T ratio), where T is cycle length. We tested the contribution of R/ T and 1/ C to Ea in 20 normotensive and 46 hypertensive subjects (MAP range: 84–160 mmHg). The multilinear model applied ( Ea = 1.00 R/ T + 0.42/ C – 0.04; r2 = 0.97). The sensitivity of Ea to a change in R/ T was 2.5 times higher than to a similar change in 1/ C in both normotensive and hypertensive adults. The LVESP was more strongly related to systolic aortic pressure (SAP; r2 = 0.94) than to MAP ( r2 = 0.83), and LVESP matched 90% SAP (bias = 0 ± 5mmHg). An alternative model of Ea is proposed, in which Ea is proportional to the heart rate × SAP product-over-cardiac index ratio whatever the MAP.
EDHF-mediated vasodilation involves different mechanisms in normotensive and hypertensive rat lungs
Authors: Morio Yoshiteru , Carter Ethan P. , Oka Masahiko , McMurtry Ivan F.
Published: March 2015

The role of endothelium-derived hyperpolarizing factor (EDHF) in regulating the pulmonary circulation and the participation of cytochrome P-450 (CYP450) activity and gap junction intercellular communication in EDHF-mediated pulmonary vasodilation are unclear. We tested whether tonic EDHF activity regulated pulmonary vascular tone and examined the mechanism of EDHF-mediated pulmonary vasodilation induced by thapsigargin in salt solution-perfused normotensive and hypoxia-induced hypertensive rat lungs. After blockade of both cyclooxygenase and nitric oxide synthase, inhibition of EDHF with charybdotoxin plus apamin did not affect either normotensive or hypertensive vascular tone or acute hypoxic vasoconstriction but abolished thapsigargin vasodilation in both groups of lungs. The CYP450 inhibitors 7-ethoxyresorufin and sulfaphenazole and the gap junction inhibitor palmitoleic acid, but not 18α-glycyrrhetinic acid, inhibited thapsigargin vasodilation in normotensive lungs. None of these agents inhibited the vasodilation in hypertensive lungs. Thus tonic EDHF activity does not regulate either normotensive or hypertensive pulmonary vascular tone or acute hypoxic vasoconstriction. Whereas thapsigargin-induced EDHF-mediated vasodilation in normotensive rat lungs involves CYP450 activity and might act through gap junctions, the mechanism of vasodilation is apparently different in hypertensive lungs.
Cardiac effects of burn injury complicated by aspiration pneumonia-induced sepsis
Authors: White Jean , Thomas James , Maass David L. , Horton Jureta W.
Published: March 2015

Early fluid resuscitation, antimicrobials, early excision, and grafting have improved survival in the early postburn period; however, a significant incidence of pneumonia-related sepsis occurs after burn injury, often progressing to multiple organ failure. Recent studies have suggested that this initial injury (burn injury) primes the subject, producing an exaggerated response to a second insult, such as pneumonia-related sepsis. We developed an experimental animal model that included a third-degree burn over 40% of the total body surface area, followed by sepsis (intratracheal administration of Streptococcus pneumoniae, 4 × 106colony-forming unit), which was produced either 48 or 72 h after burn injury in adult male rats. Hearts harvested after either burn alone, sepsis alone, or burn plus sepsis were used to assess either contractile function (Langendorff) or cardiomyocyte secretion of tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and IL-10 (ELISA). Experimental groups included the following: 1) sham (sham burn and no sepsis); 2) burn injury alone studied either 24, 48, or 72 h postburn; 3) pneumonia-related sepsis in the absence of burn injury; and 4) pneumonia-induced sepsis studied either 48 or 72 h after an initial burn injury. Burn injury alone (24 h) or sepsis alone produced myocardial contractile defects and increases in pro- and anti-inflammatory cytokine secretion by cardiomyocytes. Sepsis that occurred 48 h postburn exacerbated the cardiac contractile defects seen with either burn alone or sepsis alone. Sepsis that occurred 72 h postburn produced contractile defects resembling those seen in either burn alone or sepsis alone. In conclusion, our data suggest that burn injury primes the subject such that a second insult early in the postburn period produces significantly greater cardiac abnormalities than those seen with either burn alone or sepsis alone.
Effect of cortisol on norepinephrine-mediated contractions in ovine uterine arteries
Authors: Xiao Daliao , Huang Xiaohui , Pearce William J. , Longo Lawrence D. , Zhang Lubo
Published: March 2015

Cortisol potentiated norepinephrine (NE)-mediated contractions in ovine uterine arteries (UA). We tested the hypothesis that cortisol regulated α1-adrenoceptor-mediated pharmacomechanical coupling differentially in nonpregnant UA (NUA) and pregnant UA (PUA). Cortisol (10 ng/ml for 24 h) significantly increased contractile coupling efficiency of α1-adrenoceptors in NUA, but increased α1-adrenoceptor density in PUA. Cortisol potentiated NE-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] synthesis in both NUA and PUA, but increased coupling efficiency of α1-adrenoceptors to Ins(1,4,5)P3synthesis only in NUA. Carbenoxolone alone did not affect NE-mediated Ins(1,4,5)P3production, but significantly enhanced cortisol-mediated potentiation of NE-stimulated Ins(1,4,5)P3synthesis in PUA. In addition, cortisol potentiated the NE-induced increase in Ca2+concentration in PUA, but increased NE-mediated contraction for a given amount of Ca2+concentration in NUA. Collectively, the results indicate that cortisol potentiates NE-mediated contractions differentially in NUA and PUA, i.e., by upregulating α1-adrenoceptor density leading to increased Ca2+mobilization in PUA while increasing α1-adrenoceptor coupling efficiency and myofilament Ca2+sensitivity in NUA. In addition, the results suggest that pregnancy increases type 2 11β-hydroxysteroid dehydrogenase activity in the UA.
Manipulation of chloride flux affects histamine-induced contraction in rabbit basilar artery
Authors: Dai Yun , Zhang John H.
Published: March 2015

Cl− efflux induces depolarization and contraction of smooth muscle cells. This study was undertaken to explore the role of Cl− flux in histamine-induced contraction in the rabbit basilar artery. Male New Zealand White rabbits ( n = 16) weighing 1.8–2.5 kg were euthanized by an overdose of pentobarbital sodium. The basilar arteries were removed for isometric tension recording. Histamine produced a concentration-dependent contraction that was attenuated by the H1 receptor antagonist chlorpheniramine (10−8 M) but not by the H2 receptor antagonist cimetidine (3 × 10−6 M) in normal Cl−Krebs-Henseleit bicarbonate solution (123 mM Cl−). The histamine-induced contraction was reduced by the following manipulations: 1) inhibition of Na+-K+-2Cl− cotransporter with bumetanide (3 × 10−5 and 10−4 M), 2) bicarbonate-free HEPES solution to disable Cl−/HCO[Formula: see text] exchanger, and 3) blockade of Cl− channels with the use of niflumic acid, 5-nitro-2-(3-phenylpropylamino) benzoic acid, and indoleacetic acid 94 R-(+)-methylindazone. In addition, substitution of extracellular Cl− (10 mM) with methanesulfonate acid (113 mM) transiently enhanced histamine-induced contraction. Manipulation of Cl− flux affects histamine-induced contraction in the rabbit basilar artery.
Effect of extraction of myosin binding protein C on contractility of rat heart
Authors: Kulikovskaya I. , McClellan G. , Levine R. , Winegrad S.
Published: March 2015

Human hearts with reduced or mutant myosin binding protein C (MyBP-C) undergo hypertrophy and dilation, suggesting that reduction or alteration of MyBP-C interferes with normal contraction. Extraction of 60–70% of MyBP-C over 1 h from a mechanically disrupted cardiac myocyte has been shown to increase Ca sensitivity but does not appear to impair development of maximum Ca-activated force (Fmax). To determine whether loss of MyBP-C over a longer period of time will decrease force development in a reversible manner, MyBP-C has been extracted from chemically skinned rat cardiac trabeculae for 1–4 h, and force production, Ca sensitivity, and thick filament structure were measured. Although extraction of MyBP-C for 1 h did not alter Fmax, after 4 h, myosin heads became disordered and Fmaxdecreased. At this point, incubation of the trabeculae with rat cardiac MyBP-C in a relaxing solution reversed the decline in Fmaxand most of the change in order of myosin heads. Extraction of MyBP-C appears to produce a change in the orientation of myosin heads that is associated with a decreased ability of the contractile system to develop force.
Role of κ-opioid receptor activation in pharmacological preconditioning of swine
Authors: Coles James A. , Sigg Daniel C. , Iaizzo Paul A.
Published: March 2015

Pharmacological preconditioning with κ-opioid receptor agonists is proarrhythmic and exerts antipreconditioning effects in rats. In swine, it is unknown whether κ-opioid receptor stimulation plays a role in pharmacological preconditioning. Swine were preconditioned with 1) saline (controls), 2) [d-Ala2,d-Leu5]enkephalin (DADLE), 3) morphine, 4) pentazocine, 5) norbinaltorphimine (nor-BNI), 6) DADLE + nor-BNI, 7) morphine + nor-BNI, or 8) pentazocine + nor-BNI before occlusion (45 min) and reperfusion (180 min) of the left anterior descending coronary artery. Infarct size to area at risk (IS), regional (systolic shortening) and global (pressures and flows) myocardial function, and arrhythmia occurrence were assessed. Only DADLE + nor-BNI preconditioning significantly decreased infarct size compared with controls (47 ± 13 vs. 65 ± 5%, P < 0.05); morphine preconditioning was not cardioprotective with or without κ-opioid receptor blockade (nor-BNI). DADLE preconditioning significantly increased ischemia-induced arrhythmias relative to controls, whereas pentazocine-preconditioned animals ( n = 2) experienced intractable ventricular fibrillation during ischemia. κ-Opioid receptor blockade with DADLE or pentazocine preconditioning alleviated proarrhythmic effects. These results suggest that κ-opioid receptor activation during pharmacological preconditioning is proarrhythmic in swine.
Increased expression of alternatively spliced dominant-negative isoform of SRF in human failing hearts
Authors: Davis Francesca J. , Gupta Madhu , Pogwizd Steven M. , Bacha Emile , Jeevanandam Valluan , Gupta Mahesh P.
Published: March 2015

Serum response factor (SRF) has been shown to play a key role in cardiac cell growth and muscle gene regulation. To understand the role of SRF in heart failure, we compared its expression pattern between control and failing human heart samples. Western blot analysis of control samples showed expression of four different isoforms of SRF, with ∼67-kDa full-length SRF being the predominant isoform. Interestingly, in failing hearts we found robust expression of a low-molecular-mass (∼52 kDa) SRF isoform, accompanied by decreased expression of full-length SRF. By RT-PCR and Southern blot analyses, we characterized this ∼52-kDa SRF isoform as being encoded by an alternatively spliced form of SRF lacking exons 4 and 5 of the SRF primary RNA transcript (SRF-Δ4,5 isoform). We cloned SRF-Δ4,5 cDNA and showed that overexpression of this isoform into cells inhibits SRF-dependent activation of cardiac muscle genes. These results suggest that expression of SRF-Δ4,5 in failing hearts may in part contribute to impaired cardiac gene expression and consequently to the pathogenesis of heart failure.
Control of cardiac pyruvate dehydrogenase activity in peroxisome proliferator-activated receptor-α transgenic mice
Authors: Hopkins Teresa A. , Sugden Mary C. , Holness Mark J. , Kozak Ray , Dyck Jason R. B. , Lopaschuk Gary D.
Published: March 2015

The pyruvate dehydrogenase enzyme complex (PDC) is rate limiting for glucose oxidation in the heart. Inhibition of PDC by end-product feedback and phosphorylation by pyruvate dehydrogenase kinase (PDK) operate in concert to inhibit PDC activity. Because the transcriptional regulator peroxisome proliferator-activated receptor (PPAR)-α increases PDK expression in some tissues, we examined what role PPAR-α has in regulating glucose oxidation in hearts from mice overexpressing PPAR-α (MHC-PPAR-α mice). Glucose oxidation rates were decreased in isolated working hearts from MHC-PPAR-α mice compared with wild-type littermates (428 ± 113 vs. 771 ± 63 nmol · g dry weight-1· min-1, respectively), which was accompanied by a parallel increase in fatty acid oxidation. However, there was no difference in PDC activity between MHC-PPAR-α and wild-type animals, even though the expression of the PDK isoform PDK1 was increased in MHC-PPAR-α mice. Glucose oxidation rates in both MHC-PPAR-α and wild-type mouse hearts were decreased after 48-h fasting (which increases PPAR-α expression) or by treatment of mice with the PPAR-α agonist WY-14,643 for 1 wk. Despite this, PDC activity in both animal groups was not altered. Taken together, these data suggest that glucose oxidation rates in the heart can be dramatically altered independent of PDK phosphorylation and inhibition of PDC by PDK. It also suggests that PPAR-α activation decreases glucose oxidation in hearts mainly by decreasing the flux of pyruvate through PDC due to negative feedback of PDC by fatty acid oxidation reaction products rather than by the phosphorylated state of the PDC complex.
Triiodothyronine-mediated myosin heavy chain gene transcription in the heart
Authors: Danzi Sara , Ojamaa Kaie , Klein Irwin
Published: March 2015

We developed an RT-PCR assay to study both the time course and the mechanism for the triiodothyronine (T3)-induced transcription of the α- and β-myosin heavy chain (MHC) genes in vivo on the basis of the quantity of specific heterogeneous nuclear RNA (hnRNA). The temporal relationship of changes in transcriptional activity to the amount of α-MHC mRNA and the coordinated regulation of transcription of more than one gene in response to T3are demonstrated here for the first time. Quantitation of α-MHC hnRNA demonstrated that T3induced α-MHC transcription in hypothyroid rats within 30 min of a single injection of T3(0.5 μg/100 g body wt). Maximal transcription rates (135% ± 15.8 of euthyroid values) occurred 6 h after injection and subsequently declined in parallel with serum T3levels. The transcription of β-MHC was reduced to 86% of peak hypothyroid levels 6 h after a single T3injection and reached a nadir of 59% of hypothyroid levels at 36 h. Analysis of the time course of T3-mediated induction of α-MHC hnRNA and repression of β-MHC hnRNA indicates that separate molecular mechanisms are involved in the coordinated regulation of these genes.
Impact of estrogen replacement on ventricular myocyte contractile function and protein kinase B/Akt activation
Authors: Ren Jun , Hintz Kadon K. , Roughead Z. K. Fariba , Duan Jinhong , Colligan Peter B. , Ren Bonnie H. , Lee Kap J. , Zeng Huawei
Published: March 2015

Women with functional ovaries have a lower cardiovascular risk than men and postmenopausal women. However, estrogen replacement therapy remains controversial. This study examined the effect of ovarian hormone deficiency and estrogen replacement on ventricular myocyte contractile function and PKB/Akt activation. Nulliparous female rats were subjected to bilateral ovariectomy (Ovx) or sham operation (sham). A subgroup of Ovx rats received estrogen (E2) replacement (40 μg · kg−1 · day−1) for 8 weeks. Mechanical and intracellular Ca2+ properties were evaluated including peak shortening (PS), time to PS (TPS), time to 90% relengthening (TR90), maximal velocity of shortening/relengthening (±d L/d t), fura 2 fluorescence intensity (FFI), and decay rate. Levels of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2a), phospholamban (PLB), and Akt were assessed by Western blot. Ovx promoted body weight gain associated with reduced serum E2and uterine weight, all of which were abolished by E2. Ovx depressed PS and ±d L/d t, prolonged TPS, TR90, and decay rate, and enhanced resting FFI, all of which, with the exception of TPS, were restored by E2. Ovx did not alter the levels of SERCA2a, PLB, and total Akt, but significantly reduced Akt activation [phosphorylated Akt (pAkt)], pAkt/Akt, and the SERCA2a-to-PLB ratio. These alterations in protein expression were restored by E2. E2 enhanced PS and +d L/d t in vitro, which was abolished by the E2 receptor antagonist ICI-182780. Ovx reduced myocyte Ca2+ responsiveness and lessened stimulating frequency-induced decline in PS, both ablated by E2. These data suggest that mechanical and protein functions of ventricular myocytes are directly regulated by E2.
Action potential duration restitution and ventricular fibrillation due to rapid focal excitation
Authors: Swissa Moshe , Qu Zhilin , Ohara Toshihiko , Lee Moon-Hyoung , Lin Shien-Fong , Garfinkel Alan , Karagueuzian Hrayr S. , Weiss James N. , Chen Peng-Sheng
Published: March 2015

The focal source hypothesis of ventricular fibrillation (VF) posits that rapid activation from a focal source, rather than action potential duration (APD) restitution properties, is responsible for the maintenance of VF. We injected aconitine (100 μg) into normal isolated perfused swine right ventricles (RVs) stained with 4-{β-[2-(di- n-butylamino)-6-naphthyl]vinyl}pyridinium (di-4-ANEPPS) for optical mapping studies. Within 97 ± 163 s, aconitine induced ventricular tachycardia (VT) with a mean cycle length 268 ± 37 ms, which accelerated before converting to VF. Drugs that flatten the APD restitution slope, including diacetyl monoxime (10–20 mM, n = 6), bretylium (10–20 μg/ml, n = 3), and verapamil (2–4 μg/ml, n = 3), reversibly converted VF to VT in all cases. In two RVs, VF persisted despite of the excision of the aconitine site. Simulations in two-dimensional cardiac tissue showed that once VF was initiated, it remained sustained even after the “aconitine” site was eliminated. In this model of focal source VF, the VT-to-VF transition occurred due to a wave break outside the aconitine site, and drugs that flattened the APD restitution slope converted VF to VT despite continuous activation from aconitine site.
Nitric oxide and attenuated reflex cutaneous vasodilation in aged skin
Authors: Holowatz Lacy A. , Houghton Belinda L. , Wong Brett J. , Wilkins Brad W. , Harding Aaron W. , Kenney W. Larry , Minson Christopher T.
Published: March 2015

Thermoregulatory cutaneous vasodilation is diminished in the elderly. The goal of this study was to test the hypothesis that a reduction in nitric oxide (NO)-dependent mechanisms contributes to the attenuated reflex cutaneous vasodilation in older subjects. Seven young (23 ± 2 yr) and seven older (71 ± 6 yr) men were instrumented with two microdialysis fibers in the forearm skin. One site served as control (Ringer infusion), and the second site was perfused with 10 mM N G-nitro-l-arginine methyl ester to inhibit NO synthase (NOS) throughout the protocol. Water-perfused suits were used to raise core temperature 1.0°C. Red blood cell (RBC) flux was measured with laser-Doppler flowmetry over each microdialysis fiber. Cutaneous vascular conductance (CVC) was calculated as RBC flux per mean arterial pressure, with values expressed as a percentage of maximal vasodilation (infusion of 28 mM sodium nitroprusside). NOS inhibition reduced CVC from 75 ± 6% maximal CVC (CVCmax) to 53 ± 3% CVCmax in the young subjects and from 64 ± 5% CVCmax to 29 ± 2% CVCmax in the older subjects with a 1.0°C rise in core temperature. Thus the relative NO-dependent portion of cutaneous active vasodilation (AVD) accounted for ∼23% of vasodilation in the young subjects and 60% of the vasodilation in the older subjects at this level of hyperthermia ( P < 0.001). In summary, NO-mediated pathways contributed more to the total vasodilatory response of the older subjects at high core temperatures. This suggests that attenuated cutaneous vasodilation with age may be due to a reduction in, or decreased vascular responsiveness to, the unknown neurotransmitter(s) mediating AVD.
Expression of human smooth muscle calponin in transgenic mice revealed with a bacterial artificial chromosome
Authors: Miano Joseph M. , Kitchen Chad M. , Chen Jiyuan , Maltby Kathleen M. , Kelly Louise A. , Weiler Hartmut , Krahe Ralf , Ashworth Linda K. , Garcia Emilio
Published: March 2015

Defining regulatory elements governing cell-restricted gene expression can be difficult because cis-elements may reside tens of kilobases away from start site(s) of transcription. Artificial chromosomes, which harbor hundreds of kilobases of genomic DNA, preserve a large sequence landscape containing most, if not all, regulatory elements controlling the expression of a particular gene. Here, we report on the use of a bacterial artificial chromosome (BAC) to begin understanding the in vivo regulation of smooth muscle calponin (SM-Calp). Long and accurate polymerase chain reaction, sequencing, and in silico analyses facilitated the complete sequence annotation of a BAC harboring human SM-Calp (hSM-Calp). RNase protection, in situ hybridization, Western blotting, and immunohistochemistry assays showed the BAC clone faithfully expressed hSM-Calp in both cultured cells and transgenic mice. Moreover, expression of hSM-Calp mirrored that of endogenous mouse SM-Calp suggesting that all cis-regulatory elements governing hSM-Calp expression in vivo were contained within the BAC. These BAC mice represent a new model system in which to systematically assess regulatory elements governing SM-Calp transcription in vivo.
Increased myocardial oxygen consumption by TNF-α is mediated by a sphingosine signaling pathway
Authors: Hofmann Ulrich , Domeier Erik , Frantz Stefan , Laser Martin , Weckler Barbara , Kuhlencordt Peter , Heuer Stefan , Keweloh Boris , Ertl Georg , Bonz Andreas W.
Published: March 2015

The present study investigated the effect of tumor necrosis factor (TNF)-α on myocardial energy metabolism as estimated by myocardial oxygen consumption (MV˙o2). MV˙o2of electrically stimulated isolated trabeculae of right ventricular Wistar rat myocardium was analyzed using a Clark-type oxygen probe. After the initial data collection in the absence of TNF-α, measurements were repeated after TNF-α stimulation. In separate experiments, pretreatment with the nitric oxide (NO) synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME) or the ceramidase inhibitor n-oleoylethanolamine (NOE) was done to investigate NO/sphingosine-related effects. TNF-α impaired myocardial economy at increasing stimulation frequencies without altering baseline MV˙o2. Incubation with TNF-α in the presence of l-NAME further impaired myocardial economy. NOE preincubation abrogated the TNF-α effect on myocardial economy. Moreover, the negative inotropic effect of TNF-α was observed in NOE-pretreated but not l-NAME-pretreated muscle fibers. Exogenous sphingosine mimicked the TNF-α effect on mechanics and energetics. We conclude that TNF-α impairs the economy of chemomechanical energy transduction primarily through a sphingosine-mediated pathway.
Mechanisms mediating regional sympathoactivatory responses to stimulation of NTS A1 adenosine receptors
Authors: Scislo Tadeusz J. , O'Leary Donal S.
Published: March 2015

Selective activation of adenosine A1 and A2a receptors in the subpostremal nucleus tractus solitarius (NTS) increases and decreases mean arterial pressure (MAP), respectively, and decreases heart rate (HR). We have previously shown that the decreases in MAP evoked by NTS A2a receptor stimulation were accompanied with differential sympathetic responses in renal (RSNA), lumbar (LSNA), and preganglionic adrenal sympathetic nerve activity (pre-ASNA). Therefore, now we investigated whether stimulation of NTS A1 receptors via unilateral microinjection of N 6-cyclopentyladenosine (CPA) elicits differential activation of the same sympathetic outputs in α-chloralose-urethane-anesthetized male Sprague-Dawley rats. CPA (0.33–330.0 pmol in 50 nl) evoked dose-dependent increases in MAP, variable decreases in HR, and differential increases in all recorded sympathetic outputs: ↑pre-ASNA ≫↑RSNA ≥ ↑LSNA. Sinoaortic denervation + vagotomy abolished the MAP and LSNA responses, reversed the normal increases in RSNA into decreases, and significantly attenuated increases in pre-ASNA. NTS ionotropic glutamatergic receptor blockade with kynurenate sodium (4.4 nmol/100 nl) reversed the responses in MAP, LSNA, and RSNA and attenuated the responses in pre-ASNA. We conclude that afferent inputs and intact glutamatergic transmission in the NTS are necessary to mediate the pressor and differential sympathoactivatory responses to stimulation of NTS A1 receptors.
Protease-activated receptor-2 activation improves efficiency of experimental ischemic preconditioning
Authors: Napoli Claudio , De Nigris Filomena , Cicala Carla , Wallace John L. , Caliendo Giuseppe , Condorelli Mario , Santagada Vincenzo , Cirino Giuseppe
Published: March 2015

Protease-activated receptor-2 (PAR-2) is a member of seven transmembrane domain G protein-coupled receptors activated by proteolytic cleavage. PAR-2 is involved in inflammatory events and cardiac ischemic reperfusion injury. The objective of this study was to investigate the effects of PAR-2 in experimental myocardial ischemic preconditioning. To monitor the effects of PAR-2, Langendorff-perfused rat hearts were used. These hearts were treated with PAR-2-activating peptide (PAR-2AP) in various protocols. Hemodynamic parameters (left ventricular developed pressure, left ventricular diastolic pressure, coronary flow rate, and heart rate), several indexes of oxidative injury, and neutrophil accumulation were evaluated. We show for the first time that enhanced PAR-2 activation improves efficiency of ischemic preconditioning and reduces cardiac inflammation in the rat heart. Indeed, after PAR-2AP infusion we found that hemodynamic parameters, oxidative injury, infarct size, and neutrophil accumulation were involved. These data support the concept that PAR-2-dependent cell trafficking may regulate signaling responses to cardiac ischemia and inflammation.
Effects of heart isolation, voltage-sensitive dye, and electromechanical uncoupling agents on ventricular fibrillation
Authors: Qin Hao , Kay Matthew W. , Chattipakorn Nipon , Redden David T. , Ideker Raymond E. , Rogers Jack M.
Published: March 2015

We tested whether the interventions typically required for optical mapping affect activation patterns during ventricular fibrillation (VF). A 21 × 24 unipolar electrode array (1.5 mm spacing) was sutured to the left ventricular epicardium of 16 anesthetized pigs, and four episodes of electrically induced VF (30-s duration) were recorded. The hearts were then rapidly excised and connected to a Langendorff perfusion apparatus. Four of the hearts were controls, in which 24 additional VF episodes were then mapped. In the remaining 12 hearts, four VF episodes were mapped after isolation, four more episodes were mapped after exposure to the voltage-sensitive dye di-4-ANEPPS, and six more episodes were mapped after exposure to the electromechanical uncoupling agents diacetyl monoxime (DAM; 20 mmol/l, n = 6) or cytochalasin D (CytoD; 10 μmol/l, n = 6). VF episodes were separated by 4 min. VF activation patterns were quantified using custom pattern analysis algorithms. From comparisons with time-corrected control data, all interventions significantly changed VF patterns. Most changes were broadly consistent with slowing and regularization due to loss of excitability. Heart isolation had the largest effect on VF patterns, followed by CytoD, DAM, and dye.
Immunoglobulin treatment suppresses atherosclerosis in apolipoprotein E-deficient mice via the Fc portion
Authors: Yuan Zuyi , Kishimoto Chiharu , Sano Hideto , Shioji Keisuke , Xu Yang , Yokode Masayuki
Published: March 2015

Atherosclerosis is associated with immune activation. Immunoglobulin is used for the treatment of immune-mediated diseases. The mechanisms and importance of the Fc portion of immunoglobulin upon experimental atherosclerosis in apolipoprotein E-deficient mice were examined. Experimental atherosclerosis was induced in mice fed a high-fat diet containing 0.3% cholesterol. Over 8, 12, and 16 wk, on alternate days, mice were treated with an intraperitoneal injection of either 1 g·kg–1·day–1of human intact immunoglobulin or F(ab′)2fragments of human immunoglobulin. Fatty streak formation and fibrofatty plaques were markedly suppressed in mice that received intact immunoglobulin for 8, 12, and 16 wk. In contrast, atherosclerotic lesions were not ameliorated in mice that received F(ab′)2fragments. Immunohistochemical analysis revealed that macrophage accumulation in the fatty streak lesions was suppressed in mice received intact immunoglobulin but not in those that received F(ab′)2fragments. In addition, the cytotoxic activities of splenocytes from immunoglobulin-treated mice, but not from F(ab′)2fragment-treated mice, were significantly suppressed compared with those from human serum albumin-treated mice. Differences in lesion area did not correlate with any significant alterations in serum lipid levels. Immunoglobulin therapy markedly suppressed atherosclerosis due to Fc receptor-mediated anti-inflammatory and immunomodulating actions. The antiatherosclerotic effects of immunoglobulin may be related to the suppression of cytotoxic activity of atherogenic T cells and the reduction of macrophage accumulation in the lesions.
An integrative model of coupled water and solute exchange in the heart
Authors: Kellen Michael R. , Bassingthwaighte James B.
Published: March 2015

Physiologists have devised many models for interpreting water and solute exchange data in whole organs, but the models have typically neglected key aspects of the underlying physiology to present the simplest possible model for a given experimental situation. We have developed a physiologically realistic model of microcirculatory water and solute exchange and applied it to diverse observations of water and solute exchange in the heart. Model simulations are consistent with the results of osmotic weight transient, tracer indicator dilution, and steady-state lymph sampling experiments. The key model features that permit this unification are the use of an axially distributed blood-tissue exchange region, inclusion of a lymphatic drain in the interstitium, and the independent computation of transcapillary solute and solvent fluxes through three different pathways.
Caveolae-associated proteins in cardiomyocytes: caveolin-2 expression and interactions with caveolin-3
Authors: Rybin Vitalyi O. , Grabham Peter W. , Elouardighi Hasnae , Steinberg Susan F.
Published: March 2015

Caveolin-3 the muscle-specific caveolin isoform, acts like the more ubiquitously expressed caveolin-1 to sculpt caveolae, specialized membrane microdomains that serve as platforms to organize signal transduction pathways. Caveolin-2 is a structurally related isoform that alone does not drive caveolae biogenesis; rather, caveolin-2 cooperates with caveolin-1 to form caveolae in nonmuscle cells. Although caveolin-2 might be expected to interact in an fashion analogous to that of caveolin-3, it generally has not been detected in cardiomyocytes. This study shows that caveolin-2 and caveolin-3 are detected at low levels in ventricular myocardium and increase dramatically with age or when neonatal cardiomyocytes are placed in culture. In contrast, flotillins (caveolin functional homologs) are expressed at relatively constant levels in these preparations. In neonatal cardiac cultures, caveolin-2 and -3 expression is not influenced by thyroid hormone (a postnatal regulator of other cardiac gene products). The further evidence that caveolin-2 coimmunoprecipitates with caveolin-3 and floats with caveolin-3 by isopycnic centrifugation in cardiomyocyte cultures suggests that caveolin-2 may play a role in caveolae biogenesis and influence cardiac muscle physiology.
Vascular protection by estrogen in ischemia-reperfusion injury requires endothelial nitric oxide synthase
Authors: Prorock Alyson J. , Hafezi-Moghadam Ali , Laubach Victor E. , Liao James K. , Ley Klaus
Published: March 2015

Estrogen increases nitric oxide (NO) production by inducing the activity of endothelial NO synthase (eNOS) (Simoncini et al. Nature 407: 538, 2000). Ischemia (30 min) and reperfusion (I/R) increased the number of adherent leukocytes and decreased their rolling velocities in mouse cremaster muscle venules with a strong dependence on wall shear rate. Minimum rolling velocity at ∼5 min after the onset of reperfusion was accompanied by increased P-selectin expression. This preceded the peak in leukocyte adhesion (at 10–15 min). In untreated wild-type mice, I/R caused a decrease of leukocyte rolling velocity from 37 to 26 μm/s and a 2.0-fold increase in leukocyte adhesion. Both were completely abolished by 0.25 mg ip estrogen 1 h before surgery. In eNOS−/− mice, the decrease of leukocyte rolling velocity and increase in adhesion were similar but were only marginally improved by estrogen. We conclude that the protective effect of estrogen, as measured by leukocyte rolling and adhesion, is significantly reduced in eNOS−/− mice, suggesting that induction of eNOS activity is the major mechanism of vasoprotection by estrogen in this model.
Effects of ovariectomy on aggregation, secretion, and metalloproteinases in porcine platelets
Authors: Jayachandran Muthuvel , Owen Whyte G. , Miller Virginia M.
Published: March 2015

Differences in the aggregation and release of growth factors including matrix metalloproteinases (MMPs) after loss of ovarian hormones could contribute to an exaggerated response to injury in arteries of ovariectomized animals. Therefore, experiments were designed to compare aggregation, dense granular ATP release, expression of MMPs (MMP-2, MMP-9, and MMP-14) and tissue inhibitors of metalloproteinase (TIMP-1 and TIMP-2) in circulating platelets from sexually mature (7 mo old) gonadally intact and ovariectomized (4 wk) female pigs. Numbers of circulating platelets did not change after ovariectomy, but the percentage of reticulated platelets increased significantly. Platelet aggregation and dense granular ATP secretion also increased significantly with ovariectomy. In platelet lysates, active MMP-2 increased, whereas MMP-14 significantly decreased, after ovariectomy; the expression of TIMP-1, TIMP-2, and P-selectin did not change. These results suggest that platelet turnover, aggregation, and ATP secretion increase with ovariectomy. Also, ovarian hormones selectively regulate the expression and activity of MMPs in porcine platelets. Increased platelet aggregation and activity of MMP-2 would alter platelet-platelet and platelet-vessel wall interactions, contributing to an exaggerated response to injury with loss of ovarian hormones.
Transmural reentry triggered by epicardial stimulation during acute ischemia in canine ventricular muscle
Authors: Wu Jiashin , Zipes Douglas P.
Published: March 2015

Ischemia depresses tissue excitability more rapidly in the ventricular epicardium than in the endocardium. We hypothesized that this would provide the substrate for transmural reentry originating in the epicardium. We mapped transmural conduction in isolated and perfused wedges taken from canine left ventricles during global ischemia while pacing alternately between the epicardium and endocardium. Ischemia reduced conduction velocity more in the epicardium than in the endocardium. We observed that the epicardial-initiated activation penetrated the ventricular wall transmurally while failing to conduct laterally along the epicardium, then conducted laterally along the endocardium and midmyocardium, and reentered the epicardium in 9 of 16 wedges during epicardial stimulation after 600 ± 182 s of ischemia. Endocardial stimulation applied immediately before or after the epicardial stimulation initiated activation that spread quickly along the endocardium and then transmurally to the epicardium without reentry in six of the nine wedges. The transmural asymmetric conduction was not observed in four separate wedges after the endocardium was removed. Therefore, ischemia-induced transmural gradient of excitability provided the substrate for reentry during epicardial stimulation.
Regulation of nitric oxide-dependent vasodilation in coronary arteries of estrogen receptor-α-deficient mice
Authors: Muller-Delp Judy M. , Lubahn Dennis B. , Nichol Kathryn E. , Philips Brian J. , Price Elmer M. , Curran Edward M. , Laughlin M. Harold
Published: March 2015

Estrogen has been shown to increase endothelium-dependent vasodilation and expression of endothelial nitric oxide (NO) synthase (eNOS); however, the role of estrogen receptors in mediating estrogen effects on endothelial function remains to be elucidated. The purpose of this study was to test the hypothesis that estrogen modulates NO-dependent vasodilation of coronary arteries through its action on estrogen receptor-α (ER-α) to increase protein levels of eNOS and Cu/Zn superoxide dismutase (SOD-1). Vasodilation to acetylcholine (ACh) and sodium nitroprusside was assessed in isolated coronary arteries from intact and ovariectomized female wild-type (WT) and ER-α knockout (ERαKO) mice. Protein levels for eNOS and SOD-1 were also evaluated. Vasodilation to ACh was not significantly altered in ERαKO mice compared with WT mice. Ovariectomy reduced responsiveness to ACh in ERαKO mice but not WT mice. Responses to sodium nitroprusside were not altered by disruption of ER-α or by ovariectomy. Supplementation with estrogen restored ACh-induced vasodilation in ovariectomized ERαKO mice. eNOS protein was reduced in ERαKO mice compared with WT mice. Ovariectomy caused a further reduction in eNOS protein in ERαKO mice, but this reduction was reversed by estrogen treatment. SOD-1 protein levels were increased by disruption of ER-α. Ovariectomy reduced SOD-1 protein in ERαKO mice, but this reduction was partially reversed by estrogen replacement. These results suggest that estrogen modulation of eNOS protein content is mediated in part through ER-α. NO-dependent responses are preserved in ERαKO mice, possibly through increased SOD-1 expression and enhanced bioavailability of NO.
Pressure pulses and flow velocities in central veins of the anesthetized sheep fetus
Authors: Schröder Hobe J. , Tchirikov Mikhail , Rybakowski Christian
Published: March 2015

The pressure drop and pressure pulses in the isthmus of the ductus venosus (DV) in fetal sheep have not been measured directly and related to flow. In eight acutely anesthetized fetal sheep, a 3-Fr tip pressure transducer (TP) was inserted from the external jugular into the umbilical vein (UV). Ultrasound Doppler flow velocities, TP position, and intravenous pressures were recorded in the UV, DV, and inferior vena cava (VC) while the TP was withdrawn. Flow was steady in the UV, but small pressure fluctuations (<0.4 mmHg) could be detected. Time-averaged pressure dropped 1.9 mmHg (mean; 0.5–3.3 mmHg 95% confidence interval) across the DV isthmus. Pressure pulses increased from 1.7 mmHg (mean; 1.2–2.1 mmHg 95% confidence interval) in the DV to 3.9 mmHg (mean; 1.8–6.0 mmHg 95% confidence interval) in the inferior VC. The pressure wave from the heart arrived later [0.053 s (mean; 0.025–0.080 s 95% confidence interval)] in the isthmus of the DV than in the diaphragmatic inferior VC, indicating a wave velocity of ∼1.1 m/s. At all locations, pressures and flow velocities were inversely related.
Model of nitric oxide diffusion in an arteriole: impact of hemoglobin-based blood substitutes
Authors: Kavdia Mahendra , Tsoukias Nikolaos M. , Popel Aleksander S.
Published: March 2015

Administration of hemoglobin-based oxygen carriers (HBOCs) frequently results in vasoconstriction that is primarily attributed to the scavenging of endothelium-derived nitric oxide (NO) by cell-free hemoglobin. The ensuing pressor response could be caused by the high NO reactivity of HBOC in the vascular lumen and/or the extravasation of hemoglobin molecules. There is a need for quantitative understanding of the NO interaction with HBOC in the blood vessels. We developed a detailed mathematical model of NO diffusion and reaction in the presence of an HBOC for an arteriolar-size vessel. The HBOC reactivity with NO and degree of extravasation was studied in the range of 2–58 × 106 M−1 · s−1 and 0–100%, respectively. The model predictions showed that the addition of HBOC reduced the smooth muscle (SM) NO concentration in the activation range (12–28 nM) for soluble guanylate cyclase, a major determinant of SM contraction. The SM NO concentration was significantly reduced when the extravasation of HBOC molecules was considered. The myoglobin present in the parenchymal cells scavenges NO, which reduces the SM NO concentration.
Effect of endovascular cooling on myocardial temperature, infarct size, and cardiac output in human-sized pigs
Authors: Dae Michael W. , Gao Dong Wei , Sessler Daniel I. , Chair Kamel , Stillson Carol A.
Published: March 2015

Mild hypothermia reduces myocardial infarct size in small animals; however, the extent of myocardial protection in large animals with greater thermal mass remains unknown. We evaluated the effects of mild endovascular cooling on myocardial temperature, infarct size, and cardiac output in 60- to 80-kg isoflurane-anesthetized pigs. We occluded the left anterior descending coronary artery for 60 min, followed by reperfusion for 3 h. An endovascular heat-exchange catheter was used to either lower core body temperature to 34°C ( n = 11) or maintain temperature at 38°C ( n = 11). Additional studies assessed myocardial viability and microvascular perfusion with99mTc-sestamibi autoradiography. Endovascular cooling reduced infarct size compared with normothermia (9 ± 6% vs. 45 ± 8% of the area at risk; P < 0.001), whereas the area at risk was comparable (19 ± 3% vs. 20 ± 7%; P = 0.65). Salvaged myocardium showed normal sestamibi uptake, confirming intact microvascular flow and myocyte viability. Cardiac output was maintained in hypothermic hearts because of an increase in stroke volume, despite a decrease in heart rate. Mild endovascular cooling to 34°C lowers myocardial temperature sufficiently in human-sized hearts to cause a substantial cardioprotective effect, preserve microvascular flow, and maintain cardiac output.
Myocardial contractility by strain echocardiography: comparison with physiological measurements in an in vitro model
Authors: Abraham Theodore P. , Laskowski Carl , Zhan Wen-Zhi , Belohlavek Marek , Martin Elizabeth A. , Greenleaf James F. , Sieck Gary C.
Published: March 2015

Strain echocardiography (SE) provides the rate and extent of myocardial segment shortening and lengthening. Thus we hypothesized that SE will noninvasively provide estimates of shortening velocity (SV) and length change (δ L). We compared SE-derived strain rate (SR) and strain (ϵ) to force/length transducer-derived SV and percent δ L in isolated muscle strips at multiple load levels and under varying conditions. Electrically stimulated contractions in left ventricular muscle strips ( n = 20) were simultaneously recorded with a force/length transducer (to measure SV and percent δ L) and an ultrasound transducer (to measure SR and ϵ). Measurements were made at baseline, after inotropic stimulation, and during hypoxia at multiple load clamp levels (simulating multiple levels of afterload). Despite a difference in absolute numbers, there was a close correlation between SR and SV at baseline ( R2 = 0.95), with dobutamine treatment ( R2 = 0.99), and during hypoxia ( R2 = 0.99). SR was load dependent at baseline ( r = 0.98), with dobutamine treatment ( r = 0.99), and during hypoxia ( r = 0.92). Similarly, there was a close correlation between ϵ and δ L at baseline ( R2 = 0.99), with dobutamine treatment ( R2 = 0.96), and during hypoxia ( R2 = 0.87). Percent ϵ was load dependent at baseline ( r = 0.98), with dobutamine treatment ( r = 0.98), and during hypoxia ( r = 0.94). Bland-Altman analysis revealed a systematic overestimation of SV by SE-derived SR at baseline and with dobutamine treatment. There was no bias with SR measurements during hypoxia or with ϵ measurements. SE closely tracks standard physiological parameters of regional contractile function, such as SV and δ L, under conditions of varying afterload.