bluuebunny/crossref_metadata_2025 huggingface dataset:
Abolition of arteriolar dilation but not constriction to histamine in cremaster muscle of eNOS–/– mice
Authors: Payne Geoffrey W. , Madri Joseph A. , Sessa William C. , Segal Steven S.
Published: March 2015

Histamine increases the permeability of capillaries and venules but little is known of its precapillary actions on the control of tissue perfusion. Using gene ablation and pharmacological interventions, we tested whether histamine could increase muscle blood flow through stimulating nitric oxide (NO) release from microvascular endothelium. Vasomotor responses to topical histamine were investigated in second-order arterioles in the superfused cremaster muscle of anesthetized C57BL6 mice and null platelet endothelial cell adhesion molecule-1 (PECAM-1–/–) and null endothelial NO synthase (eNOS–/–) mice aged 8–12 wk. Neither resting (17 ± 1 μm) nor maximum diameters (36 ± 2 μm) were different between groups, nor was the constrictor response (∼5 ± 1 μm) to elevating superfusate oxygen from 0 to 21%. For arterioles of C57BL6 and PECAM-1–/– mice, cumulative addition of histamine to the superfusate produced vasodilation (1 nM–1 μM; peak response, 9 ± 1 μm) and then vasoconstriction (10–100 μM; peak response, 12 ± 2 μm). In eNOS–/– mice, histamine produced only vasoconstriction. In C57BL6 and PECAM-1–/– mice, vasodilation was abolished with Nω-nitro-l-arginine (30 μM); in all mice, vasoconstriction was abolished with nifedipine (1 μM). Vasomotor responses were eliminated with pyrilamine (1 μM; H1 receptor antagonist) yet remained intact with cimetidine (1 μM; H2 receptor antagonist). These findings illustrate that the biphasic vasomotor response of mouse cremaster arterioles to histamine is mediated through H1 receptors on endothelium (NO-dependent vasodilation) as well as smooth muscle (Ca2+ entry and constriction). Thus histamine can increase as well as decrease muscle blood flow, according to local concentration. However, when NO production is compromised, only vasoconstriction and flow reduction occur.
Increasing I Ks corrects abnormal repolarization in rabbit models of acquired LQT2 and ventricular hypertrophy
Authors: Xu Xiaoping , Salata Joseph J. , Wang Jixin , Wu Ying , Yan Gan-Xin , Liu Tengxian , Marinchak Roger A. , Kowey Peter R.
Published: March 2015

Excessive action potential (AP) prolongation and early afterdepolarizations (EAD) are triggers of malignant ventricular arrhythmias. A slowly activating delayed rectifier K+ current ( I Ks) is important for repolarization of ventricular AP. We examined the effects of I Ks activation by a new benzodiazepine (L3) on the AP of control, dofetilide-treated, and hypertrophied rabbit ventricular myocytes. In both control and hypertrophied myocytes, L3 activated I Ks via a negative shift in the voltage dependence of activation and a slowing of deactivation. L3 had no effect on L-type Ca2+ current or other cardiac K+ currents tested. L3 shortened AP of control, dofetilide-treated, and hypertrophied myocytes more at 0.5 than 2 Hz. Selective activation of I Ks by L3 attenuates prolonged AP and eliminated EAD induced by rapidly activating delayed rectifier K+ current inhibition in control myocytes at 0.5 Hz and spontaneous EAD in hypertrophied myocytes at 0.2 Hz. Pharmacological activation of I Ks is a promising new strategy to suppress arrhythmias resulting from excessive AP prolongation in patients with certain forms of long QT syndrome or cardiac hypertrophy and failure.
Cardioprotection through a PKC-dependent decrease in myofilament ATPase
Authors: Pyle W. Glen , Chen Yi , Hofmann Polly A.
Published: March 2015

Activation of myocardial κ-opioid receptor-protein kinase C (PKC) pathways may improve postischemic contractile function through a myofilament reduction in ATP utilization. To test this, we first examined the effects of PKC inhibitors on κ-opioid receptor-dependent cardioprotection. The κ-opioid receptor agonist U50,488H (U50) increased postischemic left ventricular developed pressure and reduced postischemic end-diastolic pressure compared with controls. PKC inhibitors abolished the cardioprotective effects of U50. To determine whether κ-opioid-PKC-dependent decreases in Ca2+-dependent actomyosin Mg2+-ATPase could account for cardioprotection, we subjected hearts to three separate actomyosin ATPase-lowering protocols. We observed that moderate decreases in myofibrillar ATPase were equally cardioprotective as κ-opioid receptor stimulation. Immunoblot analysis and confocal microscopy revealed a κ-opioid-induced increase in myofilament-associated PKC-ϵ, and myofibrillar Ca2+-independent PKC activity was increased after κ-opioid stimulation. This PKC-myofilament association led to an increase in troponin I and C-protein phosphorylation. Thus we propose PKC-ϵ activation and translocation to the myofilaments causes a decrease in actomyosin ATPase, which contributes to the κ-opioid receptor-dependent cardioprotective mechanism.
Smooth muscle-specific expression of SV40 large TAg induces SMC proliferation causing adaptive arterial remodeling
Authors: Sindermann Jürgen R. , Babij Philip , Klink Joseph C. , Köbbert Christiane , Plenz Gabriele , Ebbing Jan , Fan Li , March Keith L.
Published: March 2015

To study the effects of enhanced smooth muscle cell (SMC) proliferation on arterial vessel geometry in the absence of vessel trauma, we developed a transgenic mouse model expressing SV40 large T antigen under control of the 2.3-kb smooth muscle-myosin heavy chain promoter. Transgenic mice studied at ages from 3 to 13 wk showed a 3.2-fold increase in arterial wall SMC density, with 28% of SMC exhibiting proliferative cell nuclear antigen staining, confirming enhanced SMC proliferation, which was accompanied by two- to threefold increases in arterial wall areas ( P < 0.05). Remarkably, despite increased vessel wall mass, the lumen area was not compromised, but rather was increased. A tightly conserved linear relationship was found between arterial circumference and wall thickness with slopes of 0.036 for both transgenics ( r = 0.93, P < 0.01) and controls ( r = 0.77, P < 0.01), suggesting the hypothesis that the conservation of wall stress functions as a primary determinant of adaptive arterial remodeling. This establishes a new model of adaptive vessel remodeling occurring in response to a proliferative input in the absence of mechanical injury or primary flow perturbation.
Systemic and microvascular responses to hemorrhagic shock and resuscitation with Hb vesicles
Authors: Sakai Hiromi , Takeoka Shinji , Wettstein Reto , Tsai Amy G. , Intaglietta Marcos , Tsuchida Eishun
Published: March 2015

A phospholipid vesicle encapsulating hemoglobin (Hb vesicle, HbV) has been developed to provide O2-carrying capacity to plasma expanders. Its ability to restore systemic and microcirculatory conditions after hemorrhagic shock was evaluated in the dorsal skinfold window preparation of conscious hamsters. The HbV was suspended in 8% human serum albumin (HSA) at Hb concentrations of 3.8 g/dl [HbV(3.8)/HSA] and 7.6 g/dl [HbV(7.6)/HSA]. Shock was induced by 50% blood withdrawal, and mean arterial pressure (MAP) at 40 mmHg was maintained for 1 h by the additional blood withdrawal. The hamsters receiving either HbV(3.8)/HSA or HbV(7.6)/HSA suspensions restored MAP to 93 ± 14 and 93 ± 10 mmHg, respectively, similar with those receiving the shed blood (98 ± 13 mmHg), which were significantly higher by comparison with resuscitation with HSA alone (62 ± 12 mmHg). Only the HSA group tended to maintain hyperventilation and negative base excess after the resuscitation. Subcutaneous microvascular blood flow reduced to ∼10–20% of baseline during shock, and reinfusion of shed blood restored blood flow to ∼60–80% of baseline, an effect primarily due to the sustained constriction of small arteries A0 (diameter 143 ± 29 μm). The HbV(3.8)/HSA group had significantly better microvascular blood flow recovery and nonsignificantly better tissue oxygenation than of the HSA group. The recovery of base excess and improved tissue oxygenation appears to be primarily due to the increased oxygen-carrying capacity of HbV fluid resuscitation.
The neurotensin fragment AcNT(8–13) inhibits lowering of interstitial fluid pressure in rat trachea
Authors: Gjerde Eli-Anne B. , Wei Edward T. , Reed Rolf K.
Published: March 2015

Injury to soft tissue results in the lowering of interstitial fluid pressure (Pif), plasma protein extravasation, and increased total tissue volume. In this study, the effects of N-acetyl neurotensin(8–13) [AcNT(8–13)] on Pifin rat trachea were examined after electrical stimulation (ES) of the vagus nerve. Pifwas measured with glass capillaries connected to a servocontrolled counterpressure system. In pentobarbital-anesthetized female Wistar rats, the Pifafter intravenous saline was −1.8 ± 0.3 mmHg (means ± SD) and decreased to −5.0 ± 0.6 mmHg ( P < 0.01, n = 9) after ES. AcNT(8–13) (10 μg/kg) blocked the fall in Pifafter ES (−2.5 ± 2.3 mmHg, P < 0.01, n = 8). In tracheal tissue from animals pretreated with AcNT(8–13) at the same dose and immersed in phosphate-buffered saline (0.15 M, pH 7.4), the rate of fluid accumulation in excised tissues was significantly reduced after 2 h. The ability of AcNT(8–13) to modulate the fluid mechanics of tracheal interstitium after inflammation suggests that it may be a useful tool for studying cell adhesion and related factors that maintain structural integrity of connective tissue after injury.
Effect of nephrectomy and captopril on autoregulation of cerebral blood flow in rats
Authors: Pedersen Trine Fischer , Paulson Olaf B. , Nielsen Arne Høj , Strandgaard Svend
Published: March 2015

The present study investigated the effect of circulating versus locally present renin on cerebral blood flow (CBF) and its autoregulation in rats. CBF was measured repetitively with the intracarotid 133Xe injection method, whereas blood pressure was lowered to determine the lower limit of autoregulation. To remove renin from the blood, rats were bilaterally nephrectomized and kept alive with peritoneal dialysis for 48 h. Five groups of animals were studied: 1) nephrectomized dialyzed rats, 2) nephrectomized dialyzed rats given a single intravenous dose of the angiotensin-converting enzyme inhibitor captopril (10 mg/kg), 3) sham nephrectomized and dialyzed rats, 4) rats receiving drugs as dialyzed rats but no surgery, and 5) rats given the same diet as the other groups but no drugs and no surgery. Baseline blood pressure was significantly lower in nephrectomized rats compared with controls. Nephrectomy, captopril, sham operation, or dialysis did not influence baseline CBF. The lower limit of CBF autoregulation was significantly lower in nephrectomized (53 ± 4 mmHg) and sham-operated (58 ± 4 mmHg) rats compared with diet control rats (78 ± 3 mmHg). Captopril significantly decreased the lower limit in nephrectomized rats (35 ± 2 mmHg). Thus removal of circulating renin caused no change in the lower limit of autoregulation. By contrast, captopril lowered the lower limit even in the absence of circulating renin and hence appeared to exert its effect on components of the renin-angiotensin system in the cerebral resistance vessel walls.
Sexual dimorphism in prostanoid-potentiated vascular contraction: roles of endothelium and ovarian steroids
Authors: Fulton Clifford T. , Stallone John N.
Published: March 2015

The effects of constrictor prostanoid (CP) pathway inhibitors on vascular reactivity to vasopressin (VP) and phenylephrine (PE) were examined in thoracic aortas of male, female, and ovariectomized (OVX) female Sprague-Dawley rats. Maximal contractile response of control (Cont) aortas to VP was markedly higher in females (3,885 ± 332 mg/mg ring wt) than in males (810 ± 148 mg). Indomethacin (Indo; 10 μM) attenuated maximal response to VP in females (3,043 ± 277 mg) but not in males. SQ-29,548 (SQ; 1 μM) attenuated maximal response to VP in females (3,042 ± 290 mg) to a similar extent as Indo. Dazoxiben (Daz; 10 μM) alone had no effect, but Daz + SQ attenuated maximal contractile response to VP to a similar extent as SQ alone. Removal of the endothelium in female aortas attenuated contractile responses to VP in Cont aortas. OVX attenuated maximal contractile response to VP in Cont aortas (2,093 ± 329 mg) and abolished the attenuating effects of Indo. Indo, SQ, and Daz exerted identical effects on contractile responses of male, female, and OVX female aortas to PE. These findings establish the following in the rat aorta: 1) CP, probably thromboxane and/or endoperoxide, is responsible for ∼25–30% of contractile responses of females, but not males, to VP and PE; 2) CP production by the female aorta is primarily endothelial in origin; and 3) ovarian steroids modulate production and/or actions of CP in female aortas.
Transmural action potential and ionic current remodeling in ventricles of failing canine hearts
Authors: Li Gui-Rong , Lau Chu-Pak , Ducharme Anique , Tardif Jean-Claude , Nattel Stanley
Published: March 2015

Heart failure (HF) produces important alterations in currents underlying cardiac repolarization, but the transmural distribution of such changes is unknown. We therefore recorded action potentials and ionic currents in cells isolated from the endocardium, midmyocardium, and epicardium of the left ventricle from dogs with and without tachypacing-induced HF. HF greatly increased action potential duration (APD) but attenuated APD heterogeneity in the three regions. Early afterdepolarizations (EADs) were observed in all cell types of failing hearts but not in controls. Inward rectifier K+ current ( I K1) was homogeneously reduced by ∼41% (at −60 mV) in the three cell types. Transient outward K+ current ( I to1) was decreased by 43–45% at +30 mV, and the slow component of the delayed rectifier K+ current ( I Ks) was significantly downregulated by 57%, 49%, and 58%, respectively, in epicardial, midmyocardial, and endocardial cells, whereas the rapid component of the delayed rectifier K+ current was not altered. The results indicate that HF remodels electrophysiology in all layers of the left ventricle, and the downregulation of I K1, I to1, and I Ks increases APD and favors occurrence of EADs.
Minimally invasive aortic banding in mice: effects of altered cardiomyocyte insulin signaling during pressure overload
Authors: Hu Ping , Zhang Dongfang , Swenson LeAnne , Chakrabarti Gopa , Abel E. Dale , Litwin Sheldon E.
Published: March 2015

We developed a minimally invasive method for producing left ventricular (LV) pressure overload in mice. With the use of this technique, we quickly and reproducibly banded the transverse aorta with low surgical morbidity and mortality. Minimally invasive transverse aortic banding (MTAB) acutely and chronically increased LV systolic pressure, increased heart weight-to-body weight ratio, and induced myocardial fibrosis. We used this technique to determine whether reduced insulin signaling in the heart altered the cardiac response to pressure overload. Mice with cardiac myocyte-restricted knockout of the insulin receptor (CIRKO) have smaller hearts than wild-type (WT) controls. Four weeks after MTAB, WT and CIRKO mice had comparably increased LV systolic pressure, increased cardiac mass, and induction of mRNA for β-myosin heavy chain and atrial natriuretic factor. However, CIRKO hearts were more dilated, had depressed LV systolic function by echocardiography, and had greater interstitial fibrosis than WT mice. Expression of connective tissue growth factor was increased in banded CIRKO hearts compared with WT hearts. Thus lack of insulin signaling in the heart accelerates the transition to a more decompensated state during cardiac pressure overload. The use of the MTAB approach should facilitate the study of the pathophysiology and treatment of pressure-overload hypertrophy.
Nitric oxide regulates retinal vascular tone in humans
Authors: Dorner Guido T. , Garhofer Gerhard , Kiss Barbara , Polska Elzbieta , Polak Kaija , Riva Charles E. , Schmetterer Leopold
Published: March 2015

The purpose of the present study was to investigate the contribution of basal nitric oxide (NO) on retinal vascular tone in humans. In addition, we set out to elucidate the role of NO in flicker-induced retinal vasodilation in humans. Twelve healthy young subjects were studied in a three-way crossover design. Subjects received an intravenous infusion of either placebo or NG-monomethyl-l-arginine (l-NMMA; 3 or 6 mg/kg over 5 min), an inhibitor of NO synthase. Thereafter, diffuse luminance flicker was consecutively performed for 16, 32, and 64 s at a frequency of 8 Hz. The effect of l-NMMA on retinal arterial and venous diameter was assessed under resting conditions and during the hyperemic flicker response. Retinal vessel diameter was measured with a Zeiss retinal vessel analyzer. l-NMMA significantly reduced arterial diameter (3 mg/kg: –2%; 6 mg/kg: –4%, P < 0.001) and venous diameter (3 mg/kg: –5%; 6 mg/kg: –8%, P < 0.001). After placebo infusion, flicker induced a significant increase in retinal vessel diameter ( P < 0.001). At a flicker duration of 64 s, arterial diameter increased by 4% and venous diameter increased by 3%. l-NMMA did not abolish these hyperemic responses but blunted venous vasodilation ( P = 0.017) and arterial vasodilation ( P = 0.02) in response to flicker stimulation. Our data indicate that NO contributes to basal retinal vascular tone in humans. In addition, NO appears to play a role in flicker-induced vasodilation of the human retinal vasculature.
Coronary perfusion and muscle lengthening increase cardiac contraction: different stretch-triggered mechanisms
Authors: Lamberts Regis R. , van Rijen Mattie H. P. , Sipkema Pieter , Fransen Paul , Sys Stanislas U. , Westerhof Nico
Published: March 2015

An increase in coronary perfusion, transversal stretch of the myocardium, increases developed force (Fdev) (Gregg effect) through activation of stretch-activated ion channels (SACs). Lengthening of the muscle, longitudinal stretch of the myocardium, causes an immediate increase in Fdev followed by a slow Fdev increase (Anrep effect). In isometrically contracting perfused papillary muscles of Wistar rats, we investigated whether both effects were based on similar stretch-induced mechanisms by measuring Fdev and intracellular Ca2+ concentration ([Ca2+]i) after a muscle length increase from 85% to 95% L max (length at which maximal isometric force develops) at low and high coronary perfusion before and after inhibition of SACs with gadolinium (10 μmol/l Gd3+). The increase of Fdev and peak [Ca2+]i by the Gregg effect was of similar magnitude as the Anrep effect (from 3.5 ± 0.8 to 3.9 ± 1.2 mN/mm2 and from 3.0 ± 0.7% to 3.8 ± 0.9% normalized [Ca2+]i, means ± SE). SAC blockade completely blunted the increase of Fdev and peak [Ca2+]i by the Gregg effect; however, it did not affect the Anrep effect. The slow force response, but not the calcium response, was augmented by an increase in coronary perfusion. Therefore, increased coronary perfusion, transversal stretch of the myocardium, and muscle lengthening, longitudinal stretch of the myocardium, increase myocardial contraction in the rat through different stretch-triggered mechanisms.
Remodeling of the skeletal muscle microcirculation increases resistance to perfusion in obese Zucker rats
Authors: Frisbee Jefferson C.
Published: March 2015

Whereas previous studies have demonstrated that the development of syndrome X in obese Zucker rats (OZR) is associated with impaired arteriolar reactivity to vasoactive stimuli, additional results from these studies indicate that the passive diameter of skeletal muscle arterioles is reduced in OZR versus lean Zucker rats (LZR). On the basis of these prior observations, the present study evaluated structural alterations to the skeletal muscle microcirculation as potential contributors to an elevated vascular resistance. Isolated skeletal muscle resistance arterioles exhibited a reduced passive diameter at all levels of intralumenal pressure and a left-shifted stress-strain curve in OZR versus LZR, indicative of structural remodeling of individual arterioles. Histological analyses using Griffonia simplicifolia I lectin-stained sections of skeletal muscle demonstrated reduced microvessel density (rarefaction) in OZR versus LZR, suggesting remodeling of entire microvascular networks. Finally, under maximally dilated conditions, constant flow-perfused skeletal muscle of OZR exhibited significant elevations in perfusion pressure versus LZR, indicative of an increased resistance to perfusion within the microcirculation. These data suggest that developing structural alterations to the skeletal muscle microcirculation in OZR result in elevated vascular resistance, which may, acting in concert with impaired arteriolar reactivity, contribute to blunted active hyperemic responses and compromised performance of in situ skeletal muscle with elevated metabolic demand.
Pial arteriole dilation during somatosensory stimulation is not mediated by an increase in CSF metabolites
Authors: Ngai Al C. , Winn H. Richard
Published: March 2015

Pial arterioles supplying the hindlimb somatosensory cortex dilate in response to contralateral sciatic nerve stimulation. The mechanism of this pial vasodilation is not well understood. One possibility is that vasoactive metabolites released during brain activation may diffuse to subarachnoid cerebrospinal fluid (CSF) to dilate pial vessels. To test this hypothesis, we implanted closed cranial windows in rats and measured pial arteriolar dilation to sciatic nerve stimulation during constant rate superfusion of the pial surface with artificial CSF. We reason that flushing the pial surface with CSF should quickly dissipate vasoactive substances and prevent these substances from dilating pial arterioles. CSF flow (1 and 1.5 ml/min) significantly reduced pial arteriole dilation induced by 5% CO2 inhalation, but the same flow rates did not affect dilator responses to sciatic nerve stimulation. We conclude that brain-to-CSF diffusion of vasoactive metabolites does not play a significant role in the dilation of pial arterioles during somatosensory activity.
Age-associated impairment in TNF-α cardioprotection from myocardial infarction
Authors: Cai Dongqing , Xaymardan Munira , Holm Jacquelyne M. , Zheng Jingang , Kizer Jorge R. , Edelberg Jay M.
Published: March 2015

Age-associated dysfunction in cardiac microvascular endothelial cells with impaired induction of cardioprotective platelet-derived growth factor (PDGF)-dependent pathways suggests that alterations in critical vascular receptor(s) may contribute to the increased severity of cardiovascular pathology in older persons. In vivo murine phage-display peptide library biopanning revealed a senescent decrease in cardiac microvascular binding of phage epitopes homologous to tumor necrosis factor-α (TNF-α), suggesting that its receptor(s) may be downregulated in older cardiac endothelial cells. Immunostaining demonstrated that TNF-receptor 1 (TNF-R1) density was significantly lower in the subendocardial endothelium of the aging murine heart. Functional studies confirmed the senescent dysregulation of TNF-α receptor pathways, demonstrating that TNF-α induced PDGF-B expression in cardiac microvascular endothelial cells of 4-mo-old, but not 24-mo-old, rats. Moreover, TNF-α mediated cardioprotective pathways were impaired in the aging heart. In young rat hearts, injection of TNF-α significantly reduced the extent of myocardial injury after coronary ligation: TNF-α, 7.9 ± 1.9% left ventricular injury ( n = 4) versus PBS, 16.2 ± 7.9% ( n = 10; P < 0.05). The addition of PDGF-AB did not augment the cardioprotective action of TNF-α. In myocardial infarctions of older hearts, however, TNF-α induced significant postcoronary occlusion mortality (TNF-α 80% vs. PBS 0%; n = 10 each, P < 0.05) that was reversed by the coadministration of PDGF-AB. Overall, these studies demonstrate that aging-associated alterations in TNF-α receptor cardiac microvascular pathways may contribute to the increased cardiovasular pathology of the aging heart. Strategies targeted at restoring TNF-α receptor-mediated expression of PDGF-B may improve cardiac microvascular function and provide novel approaches for treatment and possible prevention of cardiovascular disease in older individuals.
Effect of gender on endothelium-dependent dilation to bradykinin in human adipose microvessels
Authors: Sato Atsushi , Miura Hiroto , Liu Yanping , Somberg Lewis B. , Otterson Mary F. , Demeure Michael J. , Schulte William J. , Eberhardt Luann M. , Loberiza Fausto R. , Sakuma Ichiro , Gutterman David D.
Published: March 2015

We examined the influence of gender and climacteric status, two coronary risk factors, on bradykinin (BK)-induced dilation in adipose arterioles from men and women of different ages [premenopausal women (Pre-W), postmenopausal women (Post-W), and similar aged men (Y-M and O-M), respectively]. We examined the responses from both omental (more closely associated with coronary disease) and subcutaneous fat. Tissues were obtained at surgery and cannulated (60 mmHg) for measurement of internal diameter. In vessels from omental tissue, dilation to BK was more sensitive in Pre-W than other groups, whereas in vessels from subcutaneous tissue, sensitivity to BK was greater in both Pre-W and Post-W compared with Y-M and O-M. Maximal dilation was similar among groups. Indomethacin (Indo; 10−5 M) alone had no effect on dilation to BK in any groups, but Indo and N ω-nitro-l-arginine methyl ester (l-NAME; 10−4 M) reduced dilation to BK in Pre-W more than in Y-M. l-NAME increased dilation to BK in subcutaneous fat from Y-M but had no effect in Post-W and O-M. Indo- and l-NAME-resistant dilation in all vessels was markedly reduced by 30 mM KCl. There was no difference in sodium nitroprusside-induced dilation among groups. We conclude that gender and climacteric state contribute to mechanisms of microvascular regulation in humans. Functional vascular differences in visceral and subcutaneous fat may underlie the proposed differential influence of these tissues on cardiovascular risk.
Mitochondrial respiratory control can compensate for intracellular O2gradients in cardiomyocytes at low Po2
Authors: Takahashi Eiji , Asano Koji
Published: March 2015

In isolated single cardiomyocytes with moderately elevated mitochondrial respiration, direct evidence for intracellular radial gradients of oxygen concentration was obtained by subcellular spectrophotometry of myoglobin (Mb). When oxygen consumption was increased by carbonyl cyanide m-chlorophenylhydrazone (CCCP) during superfusion of cells with 4% oxygen, Po2at the cell core dropped to 2.3 mmHg, whereas Mb near the plasma membrane was almost fully saturated with oxygen. Subcellular NADH fluorometry demonstrated corresponding intracellular heterogeneities of NADH, indicating suppression of mitochondrial oxidative metabolism due to relatively slow intracellular oxygen diffusion. When oxygen consumption was increased by electrical pacing in 2% oxygen, radial oxygen gradients of similar magnitude were demonstrated (cell core Po2= 2.6 mmHg). However, an increase in NADH fluorescence at the cell core was not detected. Because CCCP abolished mitochondrial respiratory control while it was intact in electrically paced cardiomyocytes, we conclude that mitochondria with intact respiratory control can sustain electron transfer with reduced oxygen supply. Thus mitochondrial intrinsic regulation can compensate for relatively slow oxygen diffusion within cardiomyocytes.
Influence of hemodynamic conditions on fractional flow reserve: parametric analysis of underlying model
Authors: Siebes Maria , Chamuleau Steven A. J. , Meuwissen Martijn , Piek Jan J. , Spaan Jos A. E.
Published: March 2015

Pressure-based fractional flow reserve (FFR) is used clinically to evaluate the functional severity of a coronary stenosis, by predicting relative maximal coronary flow (Qs/Qn). It is considered to be independent of hemodynamic conditions, which seems unlikely because stenosis resistance is flow dependent. Using a resistive model of an epicardial stenosis (0–80% diameter reduction) in series with the coronary microcirculation at maximal vasodilation, we evaluated FFR for changes in coronary microvascular resistance ( R cor= 0.2–0.6 mmHg · ml−1 · min), aortic pressure (Pa = 70–130 mmHg), and coronary outflow pressure (Pb = 0–15 mmHg). For a given stenosis, FFR increased with decreasing Pa or increasing R cor. The sensitivity of FFR to these hemodynamic changes was highest for stenoses of intermediate severity. For Pb > 0, FFR progressively exceeded Qs/Qn with increasing stenosis severity unless Pb was included in the calculation of FFR. Although the Pb-corrected FFR equaled Qs/Qn for a given stenosis, both parameters remained equally dependent on hemodynamic conditions, through their direct relationship to both stenosis and coronary resistance.
Identification of a CArG-independent region of the cysteine-rich protein 2 promoter that directs expression in the developing vasculature
Authors: Chang Yung-Fu , Wei Jiao , Liu Xiaoli , Chen Yen-Hsu , Layne Matthew D. , Yet Shaw-Fang
Published: March 2015

Cysteine-rich protein (CRP)2 is a member of the LIM-only CRP family that is expressed in vascular smooth muscle cells (VSMC). To gain insight into the transcription of CSRP2 (gene name for CRP2) in VSMC, we analyzed the 5′-flanking sequence of the CSRP2 gene. We showed previously that 4,855 bp of the 5′-flanking sequence of the CSRP2 gene directed lacZ reporter gene expression, primarily in the VSMC of transgenic mice. To further define the regulatory sequences important for CSRP2 expression in VSMC, a series of promoter constructs containing deletions of the 5′-flanking sequence upstream of a nuclear-localized lacZ reporter gene were generated and analyzed. Similar to that observed in the –4855CSRP2-lacZ mice, β-galactosidase reporter activity was detected in the developing great vessels, aorta, intersegmental arteries, umbilical vessels, endocardial cushions, and neural tube in the –3513-, –2663-, –795-, and –664CSRP2-lacZ lines. However, an internal deletion of bp –573 to –550 abolished the vascular, but not the neural tube, staining. Interestingly, no CArG box [CC(A/T)6GG] was present in the –795-bp fragment. Cotransfection experiments showed that dominant-negative serum response factor (SRF) did not repress CSRP2 promoter activity, which was different from the repressive effect of dominant-negative SRF on the SM22α promoter. Our data suggest the presence of a VSMC-specific element(s) within bp –573 to –550 of the CSRP2 5′-flanking sequence; however, in contrast to many other smooth muscle genes, transcriptional regulation of the CSRP2 gene is not dependent on SRF.
Glycated collagen cross-linking alters cardiac mechanics in volume-overload hypertrophy
Authors: Herrmann Keith L. , McCulloch Andrew D. , Omens Jeffrey H.
Published: March 2015

Alteration of hemodynamic loading induces remodeling that includes changes in myocardial properties and extracellular matrix structure. We investigated the hypothesis that cardiac hypertrophy due to volume overload produces changes in myocardial diastolic mechanics and stiffness that are in part due to alterations in advanced glycation end-product (AGE) collagen cross-linking. Rats developed volume overload induced by arteriovenous fistula (AVF). To assess the dependence of AGE cross-linking on mechanics, we prevented AGE formation by administering the drug aminoguanidine (AG) to one group of AVF rats (AG+AVF). Volume overload did not modify collagen concentration. Right ventricular AGE cross-links were modestly elevated in AVF hearts but were significantly reduced by AG. AVF rats exhibited significantly increased septal AGE cross-links that were inhibited in the AG+AVF group. AVF-induced increases in left ventricular longitudinal stiffness and septal circumferential stiffness were prevented in AG+AVF hearts. Volume overload appears to regionally modify AGE collagen cross-linking and stiffness, and AG treatment prevented these increases, demonstrating that AGE cross-linking plays a role in mediating diastolic compliance in volume-overload hypertrophy.
Sexual dimorphism in the complexity of cardiac pacemaker activity
Authors: Kuo Terry B. J. , Yang Cheryl C. H.
Published: March 2015

This study explored the effects of gender and aging on the complexity of cardiac pacemaker activity. Electrocardiogram signals were studied in normal women ( n = 240) and men ( n = 240) ranging in age from 40 to 79 yr. Nonlinear analysis of short-term resting R-R intervals was performed using the correlation dimension (CD), approximate entropy (ApEn), and largest Lyapunov exponent (LLE). Evidence of nonlinear structure was obtained by the surrogate data test. CD, ApEn, and LLE were negatively correlated with age. Despite similar means and SDs of the R-R intervals, women had a significantly higher CD, ApEn, and LLE compared with men in the age strata of 40–44 and 45–49 yr. CD and ApEn were strongly ( r > 0.71) correlated with low- and high-frequency components. We conclude that the resting cardiac pacemaker activity of women is more complex than that of men in middle age, and the gender-related difference diminishes after the age of 50 yr. The higher complexity implies a more comprehensive neural modulation.
Role of myocardium and endothelium in coronary vascular smooth muscle responses to hypoxia
Authors: Kerkhof Cornel J. M. , Van Der Linden Peter J. W. , Sipkema Pieter
Published: March 2015

Hypoxia triggers a mechanism that induces vasodilation in the whole heart but not necessarily in isolated coronary arteries. We therefore studied the role of cardiomyocytes (CM), smooth muscle cells (SMC), and endothelial cells (EC) in coronary responses to hypoxia (Po 2 of 5–10 mmHg). In an attempt to determine the factor(s) released in response to hypoxia, we inhibited the contribution of adenosine, ATP-sensitive K+ channels, prostaglandins, and nitric oxide. Isolated rat septal artery segments without (−T) and with a layer of cardiac tissue (+T) were mounted in a double wire myograph, and constriction was induced. Hypoxia induced a decrease in isometric force of 21% and 61% in −T and +T segments, respectively ( P < 0.05). EC removal increased the relaxation to hypoxia in −T segments to 33% but had the same effect in +T segments (61%). Only one of the inhibitors, the adenosine antagonist in +T segments, partially affected the relaxation due to hypoxia. The role of adenosine is thus limited and other mechanisms have to contribute. We conclude that hypoxia induces a relaxation of SMC that is augmented by the presence of CM and blunted by the endothelium. A single mediator does not induce those effects.
Acute effects of 17β-estradiol on femoral veins from adult gonadally intact and ovariectomized female pigs
Authors: Bracamonte M. P. , Jayachandran M. , Rud K. S. , Miller V. M.
Published: March 2015

Our experiments were designed to determine the acute effects of 17β-estradiol on femoral veins from intact and ovariectomized female pigs. Rings of femoral veins with or without endothelium were suspended in organ chambers for measurement of isometric force. Concentration-response curves to 17β-estradiol (10−9 to 10−5 M) were obtained in veins contracted with prostaglandin F2α in the absence and presence of inhibitors of either estrogen receptors (ICI-182780; 10−5 M), nitric oxide synthase [ N G-monomethyl-l-arginine (l-NMMA); 10−4 M], soluble guanylate cyclase (1- H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 10−5 M), or potassium channels (tetraethylammonium; 10−2 M). Estrogen receptors were identified with the use of Western blotting and immunostaining in veins of both groups. 17β-Estradiol caused acute endothelium-dependent relaxations in both groups. Relaxations to 17β-estradiol were inhibited byl-NMMA and 1- H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one but not ICI-182780. Tetraethylammonium inhibited relaxations only in veins with endothelium from intact females. Results indicate that 17β-estradiol causes acute endothelium-dependent relaxations in femoral veins. The relative contribution of nitric oxide and K+ channels as mechanisms involved in relaxations to 17β-estradiol in femoral veins is modulated by ovarian status.
Cardiovascular autonomic function correlates with the response to aerobic training in healthy sedentary subjects
Authors: Hautala Arto J. , Mäkikallio Timo H. , Kiviniemi Antti , Laukkanen Raija T. , Nissilä Seppo , Huikuri Heikki V. , Tulppo Mikko P.
Published: March 2015

Individual responses to aerobic training vary from almost none to a 40% increase in aerobic fitness in sedentary subjects. The reasons for these differences in the training response are not well known. We hypothesized that baseline cardiovascular autonomic function may influence the training response. The study population included sedentary male subjects ( n = 39, 35 ± 9 yr). The training period was 8 wk, including 6 sessions/wk at an intensity of 70–80% of the maximum heart rate for 30–60 min/session. Cardiovascular autonomic function was assessed by measuring the power spectral indexes of heart rate variability from 24-h R-R interval recordings before the training period. Mean peak O2 uptake increased by 11 ± 5% during the training period (range 2–19%). The training response correlated with age ( r = –0.39, P = 0.007) and with the values of the high-frequency (HF) spectral component of R-R intervals (HF power) analyzed over the 24-h recording ( r = 0.46, P = 0.002) or separately during the daytime hours ( r = 0.35, P = 0.028) and most strongly during the nighttime hours ( r = 0.52, P = 0.001). After adjustment for age, HF power was still associated with the training response (e.g., P = 0.001 analyzed during nighttime hours). These data show that cardiovascular autonomic function is an important determinant of the response to aerobic training among sedentary men. High vagal activity at baseline is associated with the improvement in aerobic power caused by aerobic exercise training in healthy sedentary subjects.
Influence of vascular dimension on gender difference in flow-dependent dilatation of peripheral conduit arteries
Authors: Joannides Robinson , Costentin Agathe , Iacob Michaela , Compagnon Patricia , Lahary Agnès , Thuillez Christian
Published: March 2015

To assess the influence of initial diameter on the gender difference in flow-dependent dilatation (FDD) of the conduit artery, we measured radial artery internal diameter (echotracking), flow (Doppler) and total blood viscosity in 24 healthy (25 ± 0.8 yr) men and women during reactive hyperemia (RH) and during a gradual hand skin heating (SH). At baseline, mean diameter (men, 2.76 ± 0.09 vs. women, 2.32 ± 0.07 mm, P < 0.05), flow (men, 21 ± 4 vs. women, 10 ± 1 ml/min, P < 0.05), and blood viscosity (men, 4.13 ± 0.07 vs. women, 3.92 ± 0.13 cP, P < 0.05) were higher in men but mean shear stress (MSS) was not different between groups. During RH, the percent increase in diameter was lower in men (men, 9 ± 1 vs. women, 13 ± 1%, P< 0.05). This difference was suppressed after correction for baseline diameter. During SH, the increase in diameter with flow was higher in women ( P < 0.01). However, the increase in MSS was higher in women because of their smaller diameter at each level of flow ( P < 0.01) and there was no difference between groups for the increase in diameter at each level of MSS. These results demonstrate in a direct manner that initial diameter influences the magnitude of FDD of conduit arteries in humans by modifying the value of the arterial wall shear stress at each level of flow and support the interest of the heating method in presence of heterogeneous groups.
COX-2-derived prostacyclin mediates opioid-induced late phase of preconditioning in isolated rat hearts
Authors: Shinmura Ken , Nagai Maiko , Tamaki Kayoko , Tani Masato , Bolli Roberto
Published: March 2015

Opioids confer biphasic (early and late) cardioprotection against myocardial infarction by opening mitochondrial ATP-sensitive K+channels. It is unknown whether cyclooxygenase-2 (COX-2), which mediates ischemia-induced late preconditioning, also mediates opioid-induced cardioprotection. Isolated perfused rat hearts were subjected to 20 min of global ischemia followed by 20 min of reperfusion. BW-373U86 (BW), a δ-opioid receptor agonist, was administered 1, 12, or 24 h before death. Recovery of left ventricular developed pressure (LVDP) after ischemia-reperfusion improved when BW was administered 1 or 24 h before ischemia (control: 57 ± 8, BW 1 h: 75 ± 5, BW 24 h: 85 ± 6%) but not when it was administered 12 h before (60 ± 5%). Levels of 6-keto-PGF1α(a stable metabolite of PGI2) in coronary effluent after 20 min of reperfusion were higher with 24-h BW pretreatment than in controls (1,053 ± 92 vs. 724 ± 81 pg/ml), whereas 6-keto-PGF1αlevels at baseline did not differ. Administration of a selective COX-2 inhibitor, NS-398, abolished the late phase of cardioprotection (recovery of LVDP, 53 ± 8%) and attenuated the increase in PGI2(706 ± 138 pg/ml) but did not block the early phase of cardioprotection. The selective COX-1 inhibitor SC-560 did not affect either phase of protection. Western immunoblotting revealed upregulation of PGI2synthase protein 24 h after BW administration without changes in COX-1 and COX-2 protein levels. In conclusion, the late (but not the early) phase of δ-opioid receptor-induced preconditioning is mediated by COX-2. A functional coupling between COX-2 and upregulated PGI2synthase appears to underlie this cardioprotective phenomenon in the rat.
Effects of epidermal growth factor on epinephrine-stimulated heart function in rodents
Authors: Lorita Jordi , Escalona Noèlia , Faraudo Susanna , Soley Maria , Ramı́rez Ignasi
Published: March 2015

Epidermal growth factor (EGF) interferes with β-adrenergic receptor (β-AR) signaling in adipocytes and hepatocytes, which leads to decreased lipolytic and glycogenolytic responses, respectively. We studied the effect of EGF on the heart. EGF interfered with the cAMP signal generated by β-AR agonists in cardiac myocytes. In perfused hearts, EGF decreased inotropic and chronotropic responses to epinephrine but not to 8-(4-chlorophenylthio)adenosine 3′,5′-cyclic monophosphate. Sustained epinephrine infusion induced heart contracture, which resulted in altered heart function as demonstrated by decreased inotropy and increased heart rate variability. EGF prevented all these alterations. In the whole animal (anesthetized mice), EGF administration reduced the rise in heart rate induced by a single epinephrine dose and the occurrence of Bezold-Jarisch reflex episodes induced by repeated doses. Sialoadenectomy enhanced the response to epinephrine, and EGF administration restored normal response. All these results suggest that, by interfering with β-AR signaling, EGF protects the heart against the harmful effects of epinephrine.
Central mechanisms of acute ANG II modulation of arterial baroreflex control of renal sympathetic nerve activity
Authors: Sanderford Max G. , Bishop Vernon S.
Published: March 2015

Short-term intravenous infusion of angiotensin II (ANG II) into conscious rabbits reduces the range of renal sympathetic nerve activity (RSNA) by attenuating reflex disinhibition of RSNA. This action of ANG II to attenuate the arterial baroreflex range is exaggerated when ANG II is directed into the vertebral circulation, which suggests a mechanism involving the central nervous system. Because an intact area postrema (AP) is required for ANG II to attenuate arterial baroreflex-mediated bradycardia and is also required for maintenance of ANG II-dependent hypertension, we hypothesized that attenuation of maximum RSNA during infusion of ANG II involves the AP. In conscious AP-lesioned (APX) and AP-intact rabbits, we compared the effect of a 5-min intravenous infusion of ANG II (10 and 20 ng · kg−1 · min−1) on the relationship between mean arterial blood pressure (MAP) and RSNA. Intravenous infusion of ANG II into AP-intact rabbits resulted in a dose-related attenuation of maximum RSNA observed at low MAP. In contrast, ANG II had no effect on maximum RSNA in APX rabbits. To further localize the central site of ANG II action, its effect on the arterial baroreflex was assessed after a midcollicular decerebration. Decerebration did not alter arterial baroreflex control of RSNA compared with the control state, but as in APX, ANG II did not attenuate the maximum RSNA observed at low MAP. The results of this study indicate that central actions of peripheral ANG II to attenuate reflex disinhibition of RSNA not only involve the AP, but may also involve a neural interaction rostral to the level of decerebration.
Transmural gradients of cardiac myofiber shortening in aortic valve stenosis patients using MRI tagging
Authors: Van der Toorn A. , Barenbrug P. , Snoep G. , Van der Veen F. H. , Delhaas T. , Prinzen F. W. , Maessen J. , Arts T.
Published: March 2015

Aortic valve stenosis impairs subendocardial perfusion with a risk of irreversible subendocardial tissue damage. A likely precursor of damage is subendocardial contractile dysfunction, expressed by the parameter TransDif, which is defined as epicardial minus endocardial myofiber shortening, normalized to the mean value. With the use of magnetic resonance tagging in two short-axis slices of the left ventricle (LV), TransDif was derived from LV torsion and contraction during ejection. TransDif was determined in healthy volunteers (control, n = 9) and in patients with aortic valve stenosis before (AVSten, n = 9) and 3 mo after valve replacement (AVRepl, n = 7). In the control group, TransDif was 0.00 ± 0.14 (mean ± SD). In the AVSten group, TransDif increased to 0.96 ± 0.62, suggesting impairment of subendocardial myofiber shortening. In the AVRepl group, TransDif decreased to 0.37 ± 0.20 but was still elevated. In eight of nine AVSten patients, the TransDif value was elevated individually ( P < 0.001), suggesting that the noninvasively determined parameter TransDif may provide important information in planning of treatment of aortic valve stenosis.
A possible role for atrial fibroblasts in postinfarction bradycardia
Authors: Kamkin Andre , Kiseleva Irina , Wagner Kay-Dietrich , Pylaev Alexander , Leiterer Kate P. , Theres Heinz , Scholz Holger , Günther Joachim , Isenberg Gerrit
Published: March 2015

Atrial fibroblasts are considered to modulate the contractile activity of the heart in response to mechanical stretch. In this study we examined whether atrial fibroblasts are possibly involved in bradyarrhythmia, which is a severe complication after myocardial infarction. For this purpose, transmembrane electrical potentials were recorded in cardiac fibroblasts near the sinoatrial node from sham-operated rats and from rats with myocardial infarction. Twenty days after infarction due to coronary artery ligation, the right atrial tissue weights and the sensitivity of the fibroblast membrane potential to mechanical stretch correlated positively with the infarct size. Cardiac growth was enhanced, but the stretch sensitivity and the resting membrane potential of the atrial fibroblasts declined between 8 and 30 days after infarction. The frequency of spontaneous atrial contractions was significantly reduced 8 days after myocardial infarction and recovered in parallel with the membrane potential of the fibroblasts. These findings suggest that changes in the susceptibility of atrial fibroblasts to mechanical stretch may contribute to bradyarrhythmia during postinfarct remodeling of the heart.