bluuebunny/crossref_metadata_2025 huggingface dataset:
Heme oxygenase-mediated endothelial dysfunction in DOCA-salt, but not in spontaneously hypertensive, rat arterioles
Authors: Johnson Fruzsina K. , Durante William , Peyton Kelly J. , Johnson Robert A.
Published: April 2004

Vascular heme oxygenase (HO) metabolizes heme to form carbon monoxide. Carbon monoxide inhibits nitric oxide synthase and promotes endothelium-dependent vasoconstriction. We reported HO-1-mediated endothelial dysfunction in Dahl salt-sensitive hypertension. Previous studies suggested that salt-sensitive hypertensive rats, but not spontaneously hypertensive rats (SHR), display endothelial dysfunction. This study examines the hypothesis that HO-1-mediated arteriolar endothelial dysfunction develops in deoxycorticosterone acetate (DOCA)-salt hypertensive (DOCA) rats, but not in SHR. Uninephrectomized (isoflurane anesthesia) male Sprague-Dawley rats received DOCA injections and saline drinking solution for 4 wk. Rats subjected to sham surgery received vehicle injections and tap water. Blood pressure was elevated in DOCA rats and SHR compared with sham and Wistar-Kyoto (WKY) groups. Aortic HO-1 expression and blood carboxyhemoglobin levels were elevated in the DOCA group, but not in SHR. In isolated gracilis muscle arterioles, ACh caused concentration-related vasodilation in all groups, with attenuated maximum responses in DOCA, but not in SHR, arterioles. Acute pretreatment with an inhibitor of HO, chromium mesoporphyrin, restored ACh-induced responses in DOCA arterioles to sham levels. ACh responses remained the same in SHR and WKY arterioles after chromium mesoporphyrin treatment. These data show that HO-1 levels and activity are increased and arteriolar responses to ACh are decreased in DOCA rats, but not in SHR. Furthermore, in DOCA arterioles, an inhibitor of HO restores ACh-induced vasodilation to sham levels. These results suggest that elevated HO-1 levels and activity, not resulting from hypertension per se, contribute to endothelial dysfunction in DOCA rats.
Mechanical, cellular, and molecular factors interact to modulate circulating endothelial cell progenitors
Authors: Wang Chunlin , Jiao Chunhua , Hanlon Heather D. , Zheng Wei , Tomanek Robert J. , Schatteman Gina C.
Published: April 2004

It appears that there are two classes of human circulating endothelial cell (EC) progenitors, CD34+and CD34–CD14+cells. Attention has focused on CD34+cells, yet CD34–CD14+monocytic cells are far more abundant and may represent the most common class of circulating EC progenitor. Little is known about molecular or physiological factors that regulate putative CD34–CD14+EC progenitor function, although factors secreted by other blood and cardiovascular cells to which they are exposed probably affect their behavior. Hypoxia and stretch are two important physiological stimuli known to trigger growth factors in cardiovascular cells and accordingly may modulate EC progenitors. To investigate the impact of these environmental parameters on EC progenitors, EC production in CD34–CD14+cultures was evaluated. Our data indicate that neither stretch nor hypoxia alters EC production by EC progenitors directly but do so indirectly through their effects on cardiovascular cells. Conditioned media (CM) from coronary artery smooth muscle cells inhibit EC production in culture, and this inhibition is stronger if the coronary smooth muscle cells have been subjected to cyclic stretch. In contrast, cardiomyocyte CM increases EC cell number, an effect that is potentiated if the myocytes have been subjected to hypoxia. Significantly, EC progenitor responses to CM are altered by the presence of CD34–CD14–peripheral blood mononuclear cells (PBMCs). Moreover, CD34–CD14–PBMCs attenuate EC progenitor responsiveness to the angiogenic factors basic fibroblast growth factor (FGF-2), vascular endothelial cell growth factor-A165, and erythropoietin while inducing EC progenitor death in the presence of transforming growth factor-β1in vitro
Estrogen suppresses IL-1β-mediated induction of COX-2 pathway in rat cerebral blood vessels
Authors: Ospina Jose A. , Brevig Holly N. , Krause Diana N. , Duckles Sue P.
Published: April 2004

Interleukin (IL)-1β is a potent inducer of inflammatory prostaglandins, which are important mediators of vascular response to cerebral injury, whereas estrogen reduces brain injury in models of ischemic stroke. Thus we examined the effects of in vivo IL-1β exposure on cerebrovascular cyclooxygenase (COX)-2 expression and function in an animal model of chronic estrogen replacement. Estrogen-treated and nontreated ovariectomized female rats received IL-1β injections (10 μg/kg ip), and then cerebral vessels were isolated for biochemical and contractile measurements. In estrogen-deficient rats, IL-1β induced cerebrovascular COX-2 protein expression; a peak response occurred 3 h after injection. COX-2 was localized to arterial endothelium using confocal microscopy. IL-1β increased PGE2 but not PGI2 production and decreased vascular tone as measured in isolated cerebral arteries; the latter effect was partially reversed by treatment with the selective COX-2 inhibitor NS-398 (10 μmol/l). In contrast, in animals treated with estrogen, IL-1β had no significant effect on COX-2 protein levels, PGE2 production, or vascular tone. Combined treatment with 17β-estradiol and medroxyprogesterone acetate also prevented increases in PGE2 production after IL-1β treatment, but treatment with 17α-estradiol had no effect. IL-1β induction of COX-2 protein was prevented by treatment with the nuclear factor-κB inhibitor caffeic acid phenethyl ester (20 mg/kg ip), and estrogen treatment reduced cerebrovascular nuclear factor-κB activity. Estrogen thus has potent anti-inflammatory effects with respect to cerebral vascular responses to IL-1β. These effects may have important implications for the incidence and severity of cerebrovascular disease.
Nitric oxide mediates protective effect of endothelin receptor antagonism during myocardial ischemia and reperfusion
Authors: Gonon Adrian T. , Erbas Deniz , Bröijersén Anders , Valen Guro , Pernow John
Published: April 2004

Endothelin (ET) receptor antagonism protects from ischemiareperfusion injury. We hypothesized that the cardioprotective effect is related to nitric oxide (NO) bioavailability. Buffer-perfused rat and mouse hearts were subjected to ischemia and reperfusion. At the onset of ischemia, the rat hearts received vehicle, the dual endothelin type A/type B (ETA/ETB) receptor antagonist bosentan (10 μM), the NO synthase inhibitor NG-monomethyl-l-arginine (l-NMMA; 100 μM), the combination of bosentan and l-NMMA or the combination of bosentan, l-NMMA, and the NO substrate l-arginine (1 mM). Hearts from wild-type and endothelial NO synthase (eNOS)-deficient mice received either vehicle or bosentan. Myocardial performance, endothelial function, NO outflow, and eNOS expression were monitored. Bosentan significantly improved myocardial function during reperfusion in rats and in wild-type mice, but not in eNOS-deficient mice. The functional protection afforded by bosentan was inhibited by l-NMMA, whereas it was restored by l-arginine. Myocardial expression of eNOS (immunoblotting) increased significantly in bosentan-treated rat hearts compared with vehicle hearts. Recovery of NO outflow during reperfusion was enhanced in the bosentan-treated rat heart. The endothelium-dependent vasodilator adenosine diphosphate increased coronary flow by 18 ± 9% at the end of reperfusion in the bosentan group, whereas it reduced coronary flow by 7 ± 5% in the vehicle group ( P < 0.001). The response to the endothelium-independent dilator sodium nitroprusside was not different between the two groups. In conclusion, the dual ETA/ETB receptor antagonist bosentan preserved endothelial and cardiac contractile function during ischemia and reperfusion via a mechanism dependent on endothelial NO production.
Extracellular ATP facilitates flow-induced vasodilatation in rat small mesenteric arteries
Authors: Liu Cuiling , Mather Simon , Huang Yu , Garland Christopher J. , Yao Xiaoqiang
Published: April 2004

ATP can be released from endothelial cells, and this release is increased by intraluminal flow in blood vessels. In the present study, the effect of extracellular ATP (1 μM) on flow-induced vasodilatation was investigated in isolated and pressurized rat small mesenteric arteries. In the absence of extracellular ATP, only 46% of arteries developed dilatation in response to flow, and this response was both transient and unstable. In marked contrast, with ATP present, all vessels developed a prolonged and stable dilatation in response to flow. Even in the vessels that failed to respond to flow in the absence of ATP, dilatation could be stimulated once ATP was present. The ability of ATP to facilitate flow-induced vasodilatation was mimicked by UTP (1 μM), a P2Y agonist, or 3′- O-(4-benzoyl)benzoyl ATP (BzATP; 10 μM), an agonist for P2X1, P2X7, and P2Y11 purinoceptors. The involvement of P2X7 purinoceptors was further supported by the inhibitory effect of KN-62 (1 μM), a P2X7 antagonist, on the action of BzATP. P2X1 and P2X3 purinoceptors were not involved because their receptor agonist α,β-methylene ATP had no effect. The facilitating effect of ATP on flow dilatation was also attenuated by the combined application of reactive blue 2 (100 μM), a P2Y antagonist, and suramin (100 μM), a nonselective P2X and P2Y antagonist. Furthermore, flow-induced dilatation obtained in the presence of ATP was reproducible. In contrast, in the additional presence of the ectonucleotidase inhibitor ARL-67156 (10 μM), although the first dilatation was normal, the responses to the second and later exposures to flow were greatly attenuated. The nonhydrolyzable ATP analogs adenosine-5′-(3-thiotriphosphate)trilithium salt (1 μM) and adenosine 5′-(β,γ-imido) triphosphate tetralithium salt hydrate (10 μM) had similar effects to those of ARL-67156. These data suggest that ATP acts through both P2X and P2Y purinoceptors to facilitate flow-induced vasodilatation and that ectonucleotidases prevent this effect by degrading ATP on the endothelial cell surface.
Translocation of caveolin regulates stretch-induced ERK activity in vascular smooth muscle cells
Authors: Kawabe Jun-ichi , Okumura Satoshi , Lee Ming-Chih , Sadoshima Junichi , Ishikawa Yoshihiro
Published: April 2004

Mechanical stress contributes to vascular disease related to hypertension. Activation of ERK is key to mediating cellular proliferation and vascular remodeling in response to stretch stress. However, the mechanism by which stretch mediates ERK activation in the vascular tissue is still unclear. Caveolin, a major component of a flasklike invaginated caveolae, acts as an adaptor protein for an integrin-mediated signaling pathway. We found that cyclic stretch transiently induced translocation of caveolin from caveolae to noncaveolar membrane sites in vascular smooth muscle cells (VSMCs). This translocation of caveolin was determined by detergent solubility, sucrose gradient fractionation, and immunocytochemistry. Cyclic stretch induced ERK activation; the activity peaked at 5 min (the early phase), decreased gradually, but persisted up to 120 min (the late phase). Disruption of caveolae by methyl-β-cyclodextrin, decreasing the caveolar caveolin and accumulating the noncaveolar caveolin, enhanced ERK activation in both the early and late phases. When endogenous caveolins were downregulated, however, the late-phase ERK activation was subsided completely. Caveolin, which was translocated to noncaveolar sites in response to stretch, is associated with β1-integrins as well as with Fyn and Shc, components required for ERK activation. Taken together, caveolin in caveolae may keep ERK inactive, but when caveolin is translocated to noncaveolar sites in response to stretch stress, caveolin mediates stretch-induced ERK activation through an association with β1-integrins/Fyn/Shc. We suggest that stretch-induced translocation of caveolin to noncaveolar sites plays an important role in mediating stretch-induced ERK activation in VSMCs.
Physical training and heart rate and blood pressure variability: a 5-yr randomized trial
Authors: Uusitalo Arja L. T. , Laitinen Tomi , Väisänen Sari B. , Länsimies Esko , Rauramaa Rainer
Published: April 2004

We studied the effect of regular physical activity on cardiac and vascular autonomic modulation during a 5-yr controlled randomized training intervention in a representative sample of older Finnish men. Heart rate variability (HRV) and blood pressure variability (BPV) are markers of cardiac and vascular health, reflecting cardiac and vascular autonomic modulation. One hundred and forty randomly selected 53- to 63-yr-old men were randomized into two identical groups: an intervention (EX) group and a reference (CO) group, of which 89 men remained until the final analysis (EX: n = 47; CO: n = 42). The EX group trained for 30–60 min three to five times a week with an intensity of 40–60% of maximal oxygen consumption. The mean weekly energy expenditure of the training program for the 5-yr training period was 3.80 MJ, and 71% of the EX group exceeded the mean. The EX group had a significantly ( P < 0.01) higher oxygen consumption at ventilatory aerobic threshold (V̇o2VT) than the CO group at the 5-yr time point. V̇o2VT had a tendency to increase in the EX group and decrease in the CO group (interaction P < 0.001) from the baseline to the 5-yr time point. Peak performance did not change. Low-frequency power of R-R interval variability decreased in the EX group ( P < 0.01, by 6%) from the baseline to the 5-yr time point. BPV did not change. In conclusion, low-intensity regular exercise training did not prevent HRV from decreasing or change BPV in 5 yr in older Finnish men.
Dynamic changes in expression of myosin phosphatase in a model of portal hypertension
Authors: Payne Michael C. , Zhang Hai-Ying , Shirasawa Yuichi , Koga Yasuhiko , Ikebe Mitsuo , Benoit Joseph N. , Fisher Steven A.
Published: April 2004

Myosin phosphatase is a target for signaling pathways that modulate calcium sensitivity of force production in smooth muscle. Myosin phosphatase targeting subunit 1 (MYPT1) isoforms are generated by cassette-type alternative splicing of exons in the central and 3′ portion of the transcript. Exclusion of the 3′ alternative exon, coding for the leucine zipper (LZ)-positive MYPT1 isoform, is associated with the ability to desensitize to calcium (relax) in response to NO/cGMP-dependent signaling. We examined expression of MYPT1 isoforms and smooth muscle phenotype in normal rat vessels and in a prehepatic model of portal hypertension characterized by arteriolar dilation. The large capacitance vessels, aorta, pulmonary artery, and inferior vena cava expressed predominantly the 3′ exon-out/LZ-positive MYPT1 isoform. The first-order mesenteric resistance artery (MA1) and portal vein (PV) expressed severalfold higher levels of MYPT1 with predominance of the 3′ exon-included/LZ-negative isoform. There was minor variation in the presence of the MYPT1 central alternative exons. Myosin heavy and light chain splice variants in part cosegregated with MYPT1 isoforms. In response to portal hypertension induced by PV ligature, abundance of MYPT1 in PV and MA1 was significantly reduced and switched to the LZ-positive isoform. These changes were evident within 1 day of PV ligature and were maintained for up to 10 days before reverting to control values at day 14. Alteration of MYPT1 expression was part of a complex change in protein expression that can be generalized as a modulation from a phasic (fast) to a tonic (slow) contractile phenotype. Implications of vascular smooth muscle phenotypic diversity and reversible phenotypic modulation in portal hypertension with regards to regulation of blood flow are discussed.
Mitochondrial defects and heterogeneous cytochromecrelease after cardiac cold ischemia and reperfusion
Authors: Kuznetsov Andrey V. , Schneeberger Stefan , Seiler Rüdiger , Brandacher Gerald , Mark Walter , Steurer Wolfgang , Saks Valdur , Usson Yves , Margreiter Raimund , Gnaiger Erich
Published: April 2004

Mitochondria play a critical role in myocardial cold ischemia-reperfusion (CIR) and induction of apoptosis. The nature and extent of mitochondrial defects and cytochrome c (Cyt c) release were determined by high-resolution respirometry in permeabilized myocardial fibers. CIR in a rat heart transplant model resulted in variable contractile performance, correlating with the decline of ADP-stimulated respiration. Respiration with succinate or N,N,N′, N′-tetramethyl- p-phenylenediamine dihydrochloride (substrates for complexes II and IV) was partially restored by added Cyt c, indicating Cyt c release. In contrast, NADH-linked respiration (glutamate+malate) was not stimulated by Cyt c, owing to a specific defect of complex I. CIR but not cold ischemia alone resulted in the loss of NADH-linked respiratory capacity, uncoupling of oxidative phosphorylation and Cyt c release. Mitochondria depleted of Cyt c by controlled hypoosmotic shock provided a kinetic model of homogenous Cyt c depletion. Comparison to Cyt c control of respiration in CIR-injured myocardial fibers indicated heterogeneity of Cyt c release. The complex I defect and uncoupling correlated with heterogeneous Cyt c release, the extent of which increased with loss of cardiac performance. These results demonstrate a complex pattern of multiple mitochondrial damage as determinants of CIR injury of the heart.
Dobutamine-tagged MRI for inotropic reserve assessment in severe CAD: relationship with PET findings
Authors: Mazzadi Alejandro N. , Janier Marc F. , Brossier Benjamin , André-Fouët Xavier , McFadden Eugene , Revel Didier , Croisille Pierre
Published: April 2004

The impact of blood flow reductions on the intramyocardial inotropic reserve has not yet been established in coronary artery disease (CAD). We therefore evaluated in severe CAD the relationship between positron emission tomography (PET) patterns of perfusion and glucose uptake and the corresponding tagged magnetic resonance imaging (tagged MRI) values of midmyocardial strains under low-dose dobutamine. Eighteen patients underwent tagged MRI (at rest, with dobutamine) and H 152O/18Ffluorodeoxyglucose PET. Regional midmyocardial circumferential shortening ( Ecc) and PET patterns (normal, match viable, mismatch viable, and infarcted) were assessed in three tagged MRI/PET short-axis slices. Regional Ecc at rest correlated with both perfusion ( r = 0.49) and glucose uptake ( r = 0.58). The presence of the inotropic reserve was similar in normal, match viable, and infarcted (∼40% of regions vs. 52% in mismatch viable, P < 0.05), but the extent of the increase after dobutamine was lower in infarcted regions ( P = 0.06). Within each PET pattern, regions were grouped according to their Ecc values at rest into three categories (high, intermediate, and low contractile performance). In mismatch viable (hibernation), the inotropic reserve was similar among the three categories, but in the other PET patterns the presence and extent of the inotropic reserve was higher in those regions with lowest Ecc (without significant differences in perfusion). In severe CAD, the presence of the inotropic reserve assessed by midmyocardial changes under dobutamine does not relate to resting perfusion. At a similar level of perfusion, the presence of the inotropic reserve is inversely related to contractile performance at rest, but our results suggest that it may not be true for hibernating myocardium.
A rapidly activating delayed rectifier K+ current regulates pacemaker activity in adult mouse sinoatrial node cells
Authors: Clark Robert B. , Mangoni Matteo E. , Lueger Andreas , Couette Brigitte , Nargeot Joel , Giles Wayne R.
Published: April 2004

We have investigated the physiological role of the “rapidly activating” delayed rectifier K+ current ( IKr) in pacemaker activity in isolated sinoatrial node (SAN) myocytes and the expression of mouse ether-a-go-go (mERG) genes in the adult mouse SAN. In isolated, voltage-clamped SAN cells, outward currents evoked by depolarizing steps (greater than –40 mV) were strongly inhibited by the class III methanesulfonanilide compound E-4031 (1–2.5 μM), and the deactivation “tail” currents that occurred during repolarization to a membrane potential of –45 mV were completely blocked. E-4031-sensitive currents ( IKr) reached a maximum at a membrane potential of –10 mV and showed pronounced inward rectification at more-positive membrane potentials. Activation of IKr occurred at –40 to 0 mV, with half-activation at about –24 mV. The contribution of IKr to action potential repolarization and diastolic depolarization was estimated by determining the E-4031-sensitive current evoked during voltage clamp with a simulated mouse SAN action potential. IKr reached its peak value (∼0.6 pA/pF) near –25 mV, close to the midpoint of the repolarization phase of the simulated action potential, and deactivated almost completely during the diastolic interval. E-4031 (1 μM) slowed the spontaneous pacing rate of Langendorff-perfused, isolated adult mouse hearts by an average of 36.5% ( n = 5). Expression of mRNA corresponding to three isoforms coded by the mouse ERG1 gene (mERG1), mERG1a, mERG1a′, and mERG1b, was consistently found in the SAN. Our data provide the first detailed characterization of IKr in adult mouse SAN cells, demonstrate that this current plays an important role in pacemaker activity, and indicate that multiple isoforms of mERG1 can contribute to native SAN IKr.
Effects of procainamide on electrical activity in thoracic veins and atria in canine model of sustained atrial fibrillation
Authors: Chou Chung-Chuan , Zhou Shengmei , Miyauchi Yasushi , Pak Hui-Nam , Okuyama Yuji , Fishbein Michael C. , Karagueuzian Hrayr S. , Chen Peng-Sheng
Published: April 2004

Focal discharges (FDs) are present in thoracic veins during atrial fibrillation (AF). We hypothesize that procainamide exerts its anti-AF action by suppressing FDs in the thoracic veins. We studied six mongrel dogs (22–27 kg) with sustained (>6 h) AF induced by 47 ± 20 days of chronic rapid LA appendage (LAA) or pulmonary vein (PV) pacing. Procainamide was infused intravenously until AF was terminated or a cumulative dose of 20 mg/kg was reached. High-resolution mapping during AF showed FDs in the vein of Marshall, PVs, and the LAA. Procainamide significantly ( P < 0.05) reduced the frequency of these FDs and suppressed the interactions of wave fronts between PVs and LA. The cumulative dose of PA needed to terminate AF correlated negatively ( r =–0.9, P < 0.05) with the baseline effective refractory period (ERP) of PV and positively ( r = 0.8, P < 0.05) with the baseline maximum dominant frequency (DF) of AF. In four of five dogs, AF converted to atrial tachycardia originating from the PVs before termination. Attempts to reinduce sustained AF were unsuccessful in these five dogs. AF was resistant to procainamide in the sixth dog. In conclusion, procainamide reduced the rate of FDs in the thoracic veins and the LA and suppressed the interaction between PVs and LA. Second, FDs in the PV are more resistant to procainamide's action than FDs in the atria. Third, inherent PV ERP is important in determining the antifibrillatory efficacy of procainamide.
Exercise training improves cardiac function-related gene levels through thyroid hormone receptor signaling in aged rats
Authors: Iemitsu Motoyuki , Miyauchi Takashi , Maeda Seiji , Tanabe Takumi , Takanashi Masakatsu , Matsuda Mitsuo , Yamaguchi Iwao
Published: April 2004

Exercise training improves the aging-induced downregulation of myosin heavy chain (MHC) and sarcoplasmic reticulum (SR) Ca2+-ATPase, which participate in the regulation of cardiac contraction and relaxation. Thyroid hormone receptor (TR), a transcriptional activator, affected the regulation of gene expression of MHC and SR Ca2+-ATPase. We hypothesized that myocardial TR signaling contributes to a molecular mechanism of exercise training-induced improvement of MHC and SR Ca2+-ATPase genes with cardiac function in old age. We investigated whether TR signaling and gene expression of MHC and SR Ca2+-ATPase in the aged heart are affected by exercise training, using the hearts of sedentary young rats (4 mo old), sedentary aged rats (23 mo old), and trained aged rats (23 mo old, swimming training for 8 wk). Trained aged rats showed improvement in cardiac function. Expression of TR-α1and TR-β1proteins in the heart were significantly lower in sedentary aged rats than in sedentary young rats and were significantly higher in trained aged rats than in sedentary aged rats. The activity of TR DNA binding to the transcriptional regulatory region in the α-MHC and SR Ca2+-ATPase genes and the mRNA and protein expression of α-MHC and SR Ca2+-ATPase in the heart and plasma 3,3′-triiodothyronine and thyroxine levels were altered in association with changes in the myocardial TR protein levels. These findings suggest that exercise training improves the aging-induced downregulation of myocardial TR signaling-mediated transcription of MHC and SR Ca2+-ATPase genes, thereby contributing to the improvement of cardiac function in trained aged hearts.
Inflammation- and ischemia-induced shedding of venular glycocalyx
Authors: Mulivor A. W. , Lipowsky H. H.
Published: April 2004

Alterations in the composition of the glycocalyx of venular endothelium in postcapillary venules (rat mesentery) were explored in models of inflammation and ischemia-reperfusion injury. Lectins were covalently linked to fluorescently labeled microspheres (0.1-μm diameter) or directly labeled with FITC. Adhesion of lectins specific for glucose and galactose residues of glycosaminoglycans (GAGs) and other components of the endothelial glycocalyx decreased dramatically after superfusion of the mesentery with the chemoattractant N-formylmethionyl-leucyl-phenylalanine and during reperfusion after 60-min ischemia. These reductions were significantly attenuated by superfusion with pertussis toxin (PTX), suggesting that shedding of glycocalyx was mediated by G proteins. Adhesion of microspheres linked with antibody for syndecan-1, a major proteoglycan to which GAGs are bound, revealed increased labeling as GAGs were lost and permitted greater numbers of spheres to adhere to the protein core, which was not shed. Induction of ischemia by occluding proximal microvessels for 60 min resulted in a 40% increase in galactosaminoglycans and a 15% increase in glucosaminoglycans on the endothelium, which was not inhibited by PTX. Reperfusion of vessels led to a rapid loss of GAGs that was inhibited by pretreatment with PTX, with 40% of galactosaminoglycans and 25% of glucosaminoglycans accumulated being removed by G protein-mediated shedding and the remainder freely convected away by fluid shear. We conclude that the composition of the glycocalyx results from a balance of the rate of biosynthesis of GAGs by the endothelial cell and their shedding, which may be mediated by intracellular and/or membrane-bound proteases or lyases released or activated by G protein signaling.
Systemic responses to prolonged hemorrhagic hypotension
Authors: Torres Luciana N. , Filho Ivo P. Torres , Barbee R. Wayne , Tiba M. Hakam , Ward Kevin R. , Pittman Roland N.
Published: April 2004

Studies are needed to provide a rigorous examination of the relevance of monitored variables during prolonged hemorrhagic hypotension (HH). This study was designed to investigate the parameters that describe biochemical and O2 transport patterns in animals subjected to HH. Systemic parameters that could differentiate survivors from nonsurvivors were identified. An aortic flow probe was implanted in rats ( n = 21) for continuous measurement of cardiac output. Experiments were performed 6–9 days after surgery. Rats were bled to a mean arterial pressure of 40 mmHg and kept at that level using Ringer-lactate solution. Arterial and venous blood pressures, gases, acid-base status, glucose, lactate, electrolytes, hemoglobin, O2 saturation, heart and respiratory rates, total peripheral resistance, and O2 delivery and consumption were measured before hemorrhage, soon after 40 mmHg was reached, and 0.5, 1, 2, 3, and 4 h later. Fifty-three percent of rats survived ≥3 h (survivors); others were considered nonsurvivors. Nonsurvivors showed a significantly greater degree of metabolic acidosis than survivors. Arterial Po2, respiratory rate, O2 saturation, O2 content, glucose, and pH were significantly higher in survivors. The rate of Ringer-lactate infusion, arterial K+, and Pco2 were lower in survivors. Arterial K+ and respiratory rate were the only parameters significantly different between survivors and nonsurvivors at all time points during HH. Arterial levels of K+ showed the clearest distinction between survivors and nonsurvivors and may explain the sudden death experienced by animals during HH. The data suggest that early respiratory and metabolic compensations are essential for survival of prolonged HH.
Increases in brain and cardiac AT1 receptor and ACE densities after myocardial infarct in rats
Authors: Tan Junhui , Wang Hao , Leenen Frans H. H.
Published: April 2004

In the brain, ouabain-like compounds (OLC) and the reninangiotensin system (RAS) contribute to sympathetic hyperactivity in rats after myocardial infarction (MI). This study aimed to evaluate changes in components of the central vs. the peripheral RAS. Angiotensin-converting enzyme (ACE) and angiotensin type 1 (AT1) receptor binding densities were determined by measuring 125I-labeled 351A and 125I-labeled ANG II binding 4 and 8 wk after MI. In the brain, ACE and AT1 receptor binding increased 8–15% in the subfornical organ, 14–22% in the organum vasculosum laminae terminalis, 20–34% in the paraventricular nucleus, and 13–15% in the median preoptic nucleus. In the heart, the greatest increase in ACE and AT1 receptor binding occurred at the infarct scar (∼10-fold) and the least in the right ventricle (2-fold). In kidneys, ACE and AT1 receptor binding decreased 10–15%. After intracerebroventricular infusion of Fab fragments to block brain OLC from 0.5 to 4 wk after MI, increases in ACE and AT1 receptors in the subfornical organ, organum vasculosum laminae terminalis, paraventricular nucleus, and medial preoptic nucleus were markedly inhibited, and ACE and AT1 receptor densities in the heart increased less (6-fold in the infarct scar). In kidneys, decreases in ACE and AT1 receptor binding were absent after treatment with Fab fragments. These results demonstrate that ACE and AT1 receptor binding densities increase not only in the heart but also in relevant areas of the brain of rats after MI. Brain OLC appears to play a major role in activation of brain RAS in rats after MI and, to a modest degree, in activation of the cardiac RAS.
Effects of C-type natriuretic peptide on ionic currents in mouse sinoatrial node: a role for the NPR-C receptor
Authors: Rose Robert A. , Lomax Alan E. , Kondo Colleen S. , Anand-Srivastava Madhu B. , Giles Wayne R.
Published: April 2004

The effects of C-type natriuretic peptide (CNP) on heart rate and ionic currents were demonstrated by recording the ECG from adult mice and performing voltage-clamp experiments on single sinoatrial (SA) node cells isolated from mouse heart. The selective natriuretic peptide type C receptor (NPR-C) agonist cANF (10–7M) significantly decreased heart rate in the presence of isoproterenol (5 × 10–9M), as indicated by an increase in the R-R interval of ECGs obtained from Langendorff-perfused hearts. Voltage-clamp measurements in enzymatically isolated single pacemaker myocytes revealed that CNP (10–8M) and cANF (10–8M) significantly inhibited L-type Ca2+current [ ICa(L)]. These findings suggest that the CNP effect on this current is mediated by NPR-C. Further support for an NPR-C-mediated inhibition of ICa(L)in SA node myocytes was obtained by altering the functional coupling between the G protein Giand NPR-C. In these experiments, a “Gi-activator peptide,” which consists of a 17-amino acid segment of NPR-C containing a specific Giprotein-activator sequence, was dialyzed into SA node myocytes. This peptide decreased ICa(L)significantly, suggesting that NPR-C activation can result in a reduction in ICa(L)when CNP is bound and the Giprotein pathway is activated. This effect of CNP appears to be selective for ICa(L), because the hyperpolarization-activated current was unaffected by CNP or cANF. These results provide the first demonstration that CNP has a negative chronotropic effect on heart rate and suggest that this effect is mediated by selectively activating NPR-C and reducing ICa(L)through coupling to Giprotein.
Spatial comparison between wall shear stress measures and porcine arterial endothelial permeability
Authors: Himburg Heather A. , Grzybowski Deborah M. , Hazel Andrew L. , LaMack Jeffrey A. , Li Xue-Mei , Friedman Morton H.
Published: April 2004

A better understanding of how hemodynamic factors affect the integrity and function of the vascular endothelium is necessary to appreciate more fully how atherosclerosis is initiated and promoted. A novel technique is presented to assess the relation between fluid dynamic variables and the permeability of the endothelium to macromolecules. Fully anesthetized, domestic swine were intravenously injected with the albumin marker Evans blue dye, which was allowed to circulate for 90 min. After the animals were euthanized, silicone casts were made of the abdominal aorta and its iliac branches. Pulsatile flow calculations were subsequently made in computational regions derived from the casts. The distribution of the calculated time-dependent wall shear stress in the external iliac branches was directly compared on a point-by-point basis with the spatially varying in vivo uptake of Evans blue dye in the same arteries. The results indicate that in vivo endothelial permeability to albumin decreases with increasing time-average shear stress over the normal range. Additionally, endothelial permeability increases slightly with oscillatory shear index.
Effect of prenatal hypoxia on heat stress-mediated cardioprotection in adult rat heart
Authors: Li Guohu , Bae Soochan , Zhang Lubo
Published: April 2004

Fetal programming has profound effects on cardiovascular function in later adult life. We tested the hypothesis that chronic hypoxic exposure during fetal development downregulates endogenous cardioprotective mechanisms in adult rats. Time-dated pregnant rats were divided between normoxic and hypoxic (10.5% O2 from days 15 to 21 of gestation) groups. The male progeny were studied at 2 mo of age. Rats were subjected to heat stress (42°C for 15 min). After 24 h, hearts were excised and subjected to 30 min of global ischemia and 1 h of reperfusion. Prenatal hypoxia did not change adult rat body weight and heart weight, but significantly increased the cross-sectional area of a left ventricular (LV) myocyte. Heat stress significantly improved postischemic recovery of LV function in normoxic control rats, but not in prenatally hypoxic rats. The infarct size in the LV resulting from ischemia-reperfusion was reduced by the heat stress pretreatment in control rats, but not in prenatally hypoxic rats. In accordance, heat stress significantly increased LV myocardial content of heat shock protein 70 only in normoxic control rats. In addition, there was a significant decrease in the LV myocardial content of the PKC-ϵ isoform in prenatally hypoxic rats compared with control rats. We conclude that prenatal hypoxia causes in utero programming of hsp70 gene in the LV, leading to an inhibition of its response to heat stress and a loss of cardioprotection in later adult life.
Demonstration of altered signaling responses in bone marrow extracellular fluid during increased hematopoiesis in rats using a centrifugation method
Authors: Wiig Helge , Berggreen Ellen , Borge Bengt Åge Sørby , Iversen Per Ole
Published: April 2004

The composition and characteristics of the bone marrow extracellular fluid supposedly modify the transport of cytokines, drugs, and other signaling molecules involved in the regulation of bone marrow function. Direct access to the bone marrow extracellular fluid surrounding hematopoietic cells is complicated by the virtually noncompliant surrounding bone tissue. We examined the applicability of a centrifugation method to obtain representative samples of bone marrow extracellular fluid from rats and humans. Perforated rat bones or human bone marrow biopsies were wrapped in nylon mesh baskets before being centrifuged at 180–239 g. In the rats, we found an only minor contribution of fluid from other sources than the bone marrow extracellular fluid as indicated by the average ratio of centrifugate-to-plasma activity of the extracellular tracer fluid51Cr-labeled EDTA of 0.85. The colloid osmotic pressure in the centrifugate was consistently lower than that in the corresponding plasma in both species. In rats and humans, high-performance liquid chromatography showed a protein elution pattern from the bone marrow fluid similar to that of plasma, except for a peak eluting in the ∼40-kDa molecular mass range. Western blotting of the cytokines erythropoietin and granulocyte colony-stimulating factor revealed generally higher amounts in the centrifugate than in the plasma. This difference was augmented during increased hematopoietic activity induced by inflammation or bleeding in rats. We conclude that the centrifugation method provides representative samples of bone marrow extracellular fluid and that extracellular signaling responses to altered hematopoiesis are more clearly reflected locally in the bone marrow interstitium than in plasma.
Differential contribution of necrosis and apoptosis in myocardial ischemia-reperfusion injury
Authors: McCully James D. , Wakiyama Hidetaka , Hsieh Yng-Ju , Jones Mara , Levitsky Sidney
Published: April 2004

Necrosis and apoptosis differentially contribute to myocardial injury. Determination of the contribution of these processes in ischemia-reperfusion injury would allow for the preservation of myocardial tissue. Necrosis and apoptosis were investigated in Langendorff-perfused rabbit hearts ( n = 47) subjected to 0 (Control group), 5 (GI-5), 10 (GI-10), 15 (GI-15), 20 (GI-20), 25 (GI-25), and 30 min (GI-30) of global ischemia (GI) and 120 min of reperfusion. Myocardial injury was determined by triphenyltetrazolium chloride (TTC) staining, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL), bax, bcl2, poly(ADP)ribose polymerase (PARP) cleavage, caspase-3, -8, and -9 cleavage and activity, Fas ligand (FasL), and Fas-activated death domain (FADD). The contribution of apoptosis was determined separately ( n = 42) using irreversible caspase-3, -8, and -9 inhibitors. Left ventricular peak developed pressure (LVPDP) and systolic shortening (SS) were significantly decreased and infarct size and TUNEL-positive cells were significantly increased ( P < 0.05 vs. Control group) at GI-20, GI-25, and GI-30. Proapoptotic bax, PARP cleavage, and caspase-3 and -9 cleavage and activity were apparent at GI-5 to GI-30. Fas, FADD, and caspase-8 cleavage and activity were unaltered. Irreversible inhibition of caspase-3 and -9 activity significantly decreased ( P < 0.05) infarct size at GI-25 and GI-30 but had no effect on LVPDP or SS. Myocardial injury results from a significant increase in both necrosis and apoptosis ( P < 0.05 vs. Control group) evident by TUNEL, TTC staining, and caspase activity at GI-20. Intrinsic proapoptotic activation is evident early during ischemia but does not significantly contribute to infarct size before GI-25. The contribution of necrosis to infarct size at GI-20, GI-25, and GI-30 is significantly greater than that of apoptosis. Apoptosis is significantly decreased by caspase inhibition during early reperfusion, but this protection does not improve immediate postischemic functional recovery.
Cardiac pharmacological preconditioning with volatile anesthetics: from bench to bedside?
Authors: Riess Matthias L. , Stowe David F. , Warltier David C.
Published: April 2004

A steadily increasing number of investigations demonstrate that preconditioning with volatile anesthetics attenuates the deleterious effects of myocardial ischemia and reperfusion injury by an ischemic preconditioning-like mechanism. Thus volatile anesthetics may represent the best choice for anesthesia of patients at risk for myocardial ischemia. However, factors such as old age, coexisting conditions such as diabetes mellitus and the use of oral hypoglycemic drugs or cyclooxygenase inhibitors, timing and duration of myocardial ischemia, and possible constraints of a complicated preconditioning protocol may limit the benefits of this powerful tool under clinical conditions. The purpose of this minireview is to provide a brief overview of the results of basic and clinical research on cardioprotection by volatile anesthetics.
Administration of a CO-releasing molecule at the time of reperfusion reduces infarct size in vivo
Authors: Guo Yiru , Stein Adam B. , Wu Wen-Jian , Tan Wei , Zhu Xiaoping , Li Qian-Hong , Dawn Buddhadeb , Motterlini Roberto , Bolli Roberto
Published: April 2004

Although carbon monoxide (CO) has traditionally been viewed as a toxic gas, increasing evidence suggests that it plays an important homeostatic and cytoprotective role. Its therapeutic use, however, is limited by the side effects associated with CO inhalation. Recently, transition metal carbonyls have been shown to be a safe and effective means of transporting and releasing CO groups in vivo. The goal of the present study was to test whether a water-soluble CO-releasing molecule, tricarbonylchloro(glycinato) ruthenium (II) (CORM-3), reduces infarct size in vivo when given in a clinically relevant manner, i.e., at the time of reperfusion. Mice were subjected to a 30-min coronary artery occlusion followed by 24 h of reperfusion and were given either CORM-3 (3.54 mg/kg as a 60-min intravenous infusion starting 5 min before reperfusion) or equivalent doses of inactive CORM-3, which does not release CO. CORM-3 had no effect on arterial blood pressure or heart rate. The region at risk did not differ in control and treated mice (44.5 ± 3.5% vs. 36.5 ± 1.6% of the left ventricle, respectively). However, infarct size was significantly smaller in treated mice [25.8 ± 4.9% of the region at risk ( n = 13) vs. 47.7 ± 3.8% ( n = 14), P < 0.05]. CORM-3 did not increase carboxyhemoglobin levels in the blood. These results suggest that a novel class of drugs, CO-releasing molecules, can be useful to limit myocardial ischemia-reperfusion injury in vivo.
ERK-mediated uterine artery contraction: role of thick and thin filament regulatory pathways
Authors: Xiao DaLiao , Pearce William J. , Longo Lawrence D. , Zhang Lubo
Published: April 2004

We have demonstrated that extracellular signal-regulated kinase (ERK) plays an important role in the regulation of uterine artery contraction. The present study tested the hypothesis that ERK regulates thick and thin filament regulatory pathways in the uterine artery. Isometric tension, intracellular free Ca2+concentration ([Ca2+]i), and 20-kDa myosin light chain (LC20) phosphorylation were measured simultaneously in uterine arteries isolated from near-term (140 days gestation) pregnant sheep. Phenylephrine produced time-dependent increases in [Ca2+]iand LC20phosphorylation that preceded the contraction, which were inhibited by the MEK (ERK) inhibitor PD-098059. In addition, PD-098059 decreased the intercept of the regression line of LC20phosphorylation vs. [Ca2+]ibut increased the rate of tension development vs. LC20phosphorylation. In contrast to phenylephrine, phorbol 12,13-bibutyrate (PDBu) produced contractions without changing [Ca2+]ior LC20phosphorylation. PD-098059 potentiated PDBu-induced contractions without affecting [Ca2+]iand LC20phosphorylation. PDBu produced time-dependent increases in phosphorylation of p42 and p44 ERK and ERK-dependent phosphorylation of caldesmon at Ser789in the uterine artery. PD-098059 blocked PDBu-mediated phosphorylation of p42 and p44 ERK and caldesmon. The results indicate that ERK may regulate force by a dual regulation of thick and thin filaments in uterine artery smooth muscle. ERK potentiates the thick filament regulatory pathway by enhancing LC20phosphorylation via increases in [Ca2+]iand Ca2+sensitivity of LC20phosphorylation. In contrast, ERK attenuates the thin filament regulatory pathway and suppresses contractions independent of changes in LC20phosphorylation in the uterine artery.
Heterogeneous connexin43 expression produces electrophysiological heterogeneities across ventricular wall
Authors: Poelzing Steven , Akar Fadi G. , Baron Elvera , Rosenbaum David S.
Published: April 2004

Recently we found that electrophysiological (EP) heterogeneities between subepicardial and midmyocardial cells can form a substrate for reentrant ventricular arrhythmias. However, cell-to-cell coupling through gap junctions is expected to attenuate transmural heterogeneities between cell types spanning the ventricular wall. Because connexin43 (Cx43) is the principal ventricular gap junction protein, we hypothesized that transmural EP heterogeneities are in part produced by heterogeneous Cx43 expression across the ventricular wall. The left ventricles of eight dogs were sectioned to expose the transmural surface. To determine whether heterogeneous Cx43 expression influenced EP function, high-resolution transmural optical mapping of the arterially perfused canine wedge preparation was used to measure transmural conduction velocity (θTM), dV/d tmax, transmural space constant (λTM), and transmural gradients of action potential duration (APD). Relative Cx43 expression, quantified by confocal immunofluorescence, was significantly lower (by 24 ± 17%; P < 0.05) in subepicardial compared with deeper layers. Importantly, reduced subepicardial Cx43 was associated with transmural heterogeneities of EP function evidenced by selectively reduced subepicardial θTM(by 18 ± 9%; P < 0.05) compared with deeper layers. In subepicardial regions, dV/d tmaxwas fastest (by 19 ± 15%) and λTMwas smallest (by 18.1 ± 2%), which suggests that conduction slowing was attributable to localized uncoupling rather than reduced excitability. The maximum transmural APD gradients occurred in the same regions where Cx43 expression was lowest; this suggests that Cx43 expression patterns served to maintain APD gradients across the transmural wall. These data demonstrate that heterogeneous Cx43 expression is closely associated with functionally significant EP heterogeneities across the transmural wall. Therefore, Cx43 expression patterns can potentially contribute to arrhythmic substrates that are dependent on transmural electrophysiological heterogeneities.