bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of the endothelial glycocalyx in dromotropic, inotropic, and arrythmogenic effects of coronary flow
Authors: Rubio Rafael , Ceballos Guillermo
Published: December 2017

Coronary flow regulates cardiac functions, and it has been suggested that endothelial membrane glycosylated proteins are the primary shear stress mechanosensors. Our hypothesis was that if these proteins are the sensors for flow, then intracoronary perfusion of lectins or specific antibodies should differentially depress coronary flow-enhanced responses of different parenchymal cell types such as auricular-ventricular (A-V) nodal cells (dromotropic effect), contractile myocytes (inotropic effect), and junctional Purkinje-muscle cells (spontaneous ventricular rhythm). The coronary flow stimulatory effects on A-V delay and spontaneous ventricular rhythm were selectively depressed by six of eight lectins. None of the lectins depressed the coronary flow inotropic effect. Antibodies against endothelial surface proteins, αvβ5-integrin and sialyl-Lewisb glycan, depressed the dromotropic but not the inotropic effects of coronary flow, whereas the vascular cell adhesion molecule 1 antibody had no effect on the dromotropic, but enhanced the inotropic, effect. The fact that lectins and antibodies differentially depressed regional coronary flow effects suggests that there is a chemical distinctiveness in their intravascular endothelial cell surfaces. However, nonselective cross-linking of endothelial glycocalyx proteins with 2,000-kDa dextran-aldehyde or vitronectin indistinctively depressed the dromotropic and inotropic effects of coronary flow. These results indicate that coronary flow-induced stress acts on specific structures located in the capillary intravascular membrane glycocalyx.
oxLDLspecifically impairs endothelium-dependent, NO-mediated dilation of coronary arterioles
Authors: Hein Travis W. , Liao James C. , Kuo Lih
Published: December 2017

Our previous studies implicated that oxidized low-density lipoprotein (oxLDL), a putative atherogenic agent, impairs endothelium-dependent, nitric oxide (NO)-mediated dilation of isolated coronary arterioles to pharmacological agonists. However, it is not known whether oxLDL specifically affects NO-mediated dilation or generally impairs endothelium-dependent function, including the release of hyperpolarizing factors. In this regard, we investigated the dilation of isolated porcine coronary arterioles (50- to 100-μm luminal diameter) in response to the activation of various endothelium-dependent pathways before and after intraluminal incubation of the vessels with oxLDL (0.5 mg protein/ml for 60 min). In the absence of oxLDL, all vessels developed basal tone and dilated in response to the activation of NO synthase (by flow and adenosine), cyclooxygenase (by arachidonic acid), cytochrome P-450 monooxygenase (by bradykinin), and endothelial membrane hyperpolarization (by sucrose-induced hyperosmolarity). Incubation of the vessels with oxLDL for 60 min did not alter basal tone but did inhibit the vasodilatory responses to increased flow and adenosine in a manner similar to that of the NO synthase inhibitor NG-nitro-l-arginine methyl ester. Vasodilations in response to flow and adenosine were not affected by intraluminal incubation of the vessels with either a vehicle solution or the native LDL (0.5 mg protein/ml, 60 min). In contrast with the NO-mediated response, hyperosmotic vasodilation mediated by endothelial hyperpolarization was not affected by oxLDL. Endothelium-dependent dilations to the cyclooxygenase activator arachidonic acid and to the cytochrome P-450 monooxygenase activator bradykinin and endothelium-independent vasodilation to sodium nitroprusside were also not altered by oxLDL. Collectively, these results indicate that oxLDL has a selective effect on endothelium-dependent dilation with specific impairment of the NO-mediated response, whereas cyclooxygenase and cytochrome P-450 monooxygenase-mediated dilations are spared from this inhibitory effect. In addition, oxLDL does not appear to affect vasodilation mediated by hyperpolarization of the endothelium.
Cholesterol feeding exacerbates myocardial injury in Zucker diabetic fatty rats
Authors: Hoshida Shiro , Yamashita Nobushige , Otsu Kinya , Kuzuya Tsunehiko , Hori Masatsugu
Published: December 2017

We measured infarct size after coronary occlusion (30 min) and reperfusion (24 h) in genetic non-insulin-dependent Zucker diabetic fatty (ZDF) rats with and without 4-wk cholesterol feeding. Infarct size was similar in ZDF rats and lean control rats but was significantly larger in cholesterol-fed diabetic rats than in cholesterol-fed lean rats ( P < 0.05). Plasma levels of glucose, insulin, and triglycerides were significantly higher in diabetic rats and were not influenced by cholesterol feeding. The increase in total plasma cholesterol induced by cholesterol feeding was significantly greater in diabetic rats than in lean rats ( P < 0.05). A significant positive correlation was found between total plasma cholesterol and infarct size ( P < 0.05). Myeloperoxidase activity, as an index of neutrophil accumulation, was significantly higher and expression of P-selectin was more marked in the ischemic myocardium of cholesterol-fed diabetic rats than of cholesterol-fed lean rats. Acetylcholine-induced endothelium-dependent relaxation (EDR) of aortic rings was markedly impaired in cholesterol-fed diabetic rats. Thus cholesterol feeding significantly exacerbated myocardial injury produced by coronary occlusion-reperfusion in non-insulin-dependent diabetic rats, possibly because of enhanced expression of P-selectin and impairment of EDR in the coronary bed.
Regulation of endothelial nitric oxide synthase by PGD2 in the developing choroid
Authors: Dumont Isabelle , Hardy Pierre , Peri Krishna G. , Hou Xin , Molotchnikoff Stéphane , Varma Daya R. , Chemtob Sylvain
Published: December 2017

We investigated if prostaglandins might regulate the increased choroidal endothelial (e) nitric oxide synthase (NOS) expression in the perinate. Prostaglandins, eNOS mRNA, immunoreactive protein and activity, and nitrite [stable metabolite of nitric oxide (NO)] production were markedly higher in newborn (1 day old) than juvenile (6–8 wk old) pig choroid. Treatment of isolated newborn choroids with the prostaglandin synthase inhibitor ibuprofen for 24 h reduced eNOS mRNA and nitrite production to values in juveniles. This effect was equally observed with the PGD2 receptor (DP) blocker BW A868C and was prevented by cotreatment with PGD2 but not other prostaglandins; similar observations were made on NOS activity in vivo. PGD2 also increased eNOS expression on choroids of juveniles, and this effect was blocked by BW A868C. The manifestation of this upregulation of eNOS by PGD2 on the control of choroidal vasomotor response was tested by using NO-dependent vasorelaxants, ACh, bradykinin (Bk), and substance P (SP). ACh-, Bk-, and SP-elicited choroidal vasorelaxation was greater in saline-treated newborn than juvenile pigs. Ibuprofen (24 h) decreased ACh-, Bk-, and SP-evoked vasorelaxation in newborns, whereas PGD2 increased that in juveniles and prevented the ibuprofen-induced attenuated relaxation in newborns; infusion of N ω-monomethyl-l-arginine in choroids of those animals treated with PGD2 reversed the augmented vasorelaxation to ACh, Bk, and SP. Finally, PGD2-induced upregulation of NOS in the perinate was also reflected by curtailed choroidal blood flow autoregulatory response to increased perfusion pressure. In conclusion, PGD2 exhibits a major role in upregulating eNOS expression and activity in the choroid, which in turn results in greater NO-mediated vasorelaxation; a new mechanism for eNOS regulation via DP is hereby disclosed. The relationship between PGD2 and eNOS in the developing subject provides an explanation for the interactive role of these two factors in the absent choroidal blood flow autoregulation in the perinate.
Increased aortic stiffness assessed by pulse wave velocity in apolipoprotein E-deficient mice
Authors: Wang Yi-Xin , Halks-Miller Meredith , Vergona Ron , Sullivan Mark E. , Fitch Richard , Mallari Cornell , Martin-McNulty Baby , da Cunha Valdeci , Freay Ana , Rubanyi Gabor M. , Kauser Katalin
Published: December 2017

Atherosclerosis develops and progresses spontaneously in apolipoprotein E-knockout (apoE-KO) mice. A direct consequence of atherosclerosis is an increase in vascular stiffness. Pulse wave velocity (PWV) has been used to assess the stiffness of large vessels and was found to be increased in patients with atherosclerosis. In the present study, aortic stiffness was assessed by PWV in 4- and 13-mo-old apoE-KO mice and age-matched controls (C57BL/6J). In 13-mo-old apoE-KO mice with extensive atherosclerotic lesions in the aorta (61 ± 4%), PWV increased significantly (3.8 ± 0.2 m/s) compared with controls (2.9 ± 0.2 m/s). Endothelial nitric oxide (EDNO)-mediated vasorelaxation in response to ACh was markedly diminished in the aortic rings isolated from 13-mo-old apoE-KO mice compared with age-matched controls. In contrast, in 4-mo-old apoE-KO mice with only moderate atherosclerotic lesions in the aorta (23 ± 5%), there were no significant changes in PWV and EDNO-mediated relaxation compared with controls. Blood pressure was not different among the four groups of mice. There were no significant differences in endothelium-independent vascular responses to sodium nitroprusside among different groups investigated. Histological evaluation revealed focal fragmentation of the elastic laminae in the aortic walls of 13-mo-old apoE-KO mice. These results demonstrate for the first time that aortic stiffness determined by PWV increases in 13-mo-old apoE-KO mice. Endothelial dysfunction and elastic destruction in vascular wall caused by atherosclerosis may have contributed.
Mechanical stretch stimulates growth of vascular smooth muscle cells via epidermal growth factor receptor
Authors: Iwasaki Hiroaki , Eguchi Satoru , Ueno Hikaru , Marumo Fumiaki , Hirata Yukio
Published: December 2017

We have studied whether activation of epidermal growth factor receptor (EGFR) is involved in stretch-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation and protein synthesis in cultured rat vascular smooth muscle cells (VSMC). Cyclic stretch (1 Hz) induced a rapid (within 5 min) phosphorylation of ERK1/2, an effect that was time and strength dependent and inhibited by an EGFR kinase inhibitor (AG-1478) but not by a platelet-derived growth factor receptor kinase inhibitor (AG-1296). The stretch rapidly (within 2 min) induced tyrosine phosphorylation of several proteins, among which 180-kDa protein was shown to be EGFR as revealed by blockade with AG-1478 as well as immunoprecipitation with anti-EGFR antibody coupled with immunoblotting with anti-phosphotyrosine antibody. The stretch rapidly (within 2 min) induced association of tyrosine-phosphorylated EGFR with adaptor proteins (Shc/Grb2) as revealed by coprecipitation with glutathione- S-transferase-Grb2 fusion protein coupled with immunoblotting with anti-phosphotyrosine, anti-EGFR, and anti-Shc antibodies. Transfection of a dominant-negative mutant of H-Ras also inhibited stretch-induced ERK1/2 activation. Treatment with a stretch-activated ion channel blocker (Gd3+) and an intracellular Ca2+ antagonist (TMB-8) inhibited stretch-induced phosphorylation of EGFR and ERK1/2. Treatment with AG-1478 and a mitogen-activated protein kinase kinase inhibitor (PD-98059), but not AG-1296, blocked [3H]leucine uptake stimulated by a high level of stretch. These data suggest that ERK1/2 activation by mechanical stretch requires Ca2+-sensitive EGFR activation mainly via stretch-activated ion channels, thereby leading to VSMC growth.
AT1 receptor inhibition does not reduce arterial wall hypertrophy or PDGF-A expression in renal hypertension
Authors: Parker Sheri B. , Dobrian Anca D. , Wade Suzanne S. , Prewitt Russell L.
Published: December 2017

To separate the role of ANG II from pressure in hypertrophy of the vascular wall in one-kidney, one-clip (1K1C) hypertension, experimental and sham-operated rats were given the AT1-receptor antagonist losartan (20 mg ⋅ kg− 1 ⋅ day− 1) or tap water for 14 days. Mean arterial pressure was elevated in both experimental groups compared with controls. Rats were anesthetized with pentobarbital sodium, and the thoracic aorta and carotid, small mesenteric, and external spermatic arteries were harvested and embedded in paraffin. Tissue sections were used for morphological analysis, immunohistochemistry for 5-bromo-2′-deoxyuridine (BrdU) and platelet-derived growth factor (PDGF)-AA, stereological measurements, and in situ hybridization with a 35S-labeled riboprobe for PDGF-A mRNA. Elevated cross-sectional areas of thoracic, carotid, and small mesenteric artery in 1K1C rats were not reduced by losartan. The internal diameter of the external spermatic artery and microvascular density of the cremaster muscle were reduced in 1K1C rats. The number of BrdU-positive nuclei per cross section did not differ between 1K1C and control arteries. PDGF-A mRNA was elevated in the arterial walls of 1K1C rats compared with controls and was hardly changed by losartan. PDGF-A protein stained strongly in the media of 1K1C arteries and was not inhibited by losartan; it appeared in the adventitia of all aortas and carotid arteries. These observations demonstrate that effects of ANG II mediated through the AT1 receptor are not necessary for hypertrophy of the vascular wall during 1K1C hypertension or expression of PDGF-A.
Ventricular adrenomedullin concentration is a sensitive biochemical marker for volume and pressure overload in rats
Authors: Yoshihara Fumiki , Nishikimi Toshio , Horio Takeshi , Yutani Chikao , Nagaya Noritoshi , Matsuo Hisayuki , Ohe Tohru , Kangawa Kenji
Published: December 2017

This study was designed to investigate the pathophysiological significance of adrenomedullin (AM) concentration in volume- and pressure-overloaded cardiac hypertrophy. We measured ventricular AM concentrations and compared them with changes of α-actin and myosin heavy chain (MHC) mRNA isoforms after the creation of an aortocaval (AC) shunt as a volume-overload model or the injection of monocrotaline (MCT) as a pressure-overload model, respectively. The left ventricular AM levels after the creation of AC shunt and the right ventricular AM levels after the injection of MCT were significantly increased and correlated with changes of the α-actin and MHC mRNA isoforms. However, the ventricular AM mRNA expressions were increased and correlated with ventricular AM concentrations only in the AC shunt model. These results suggest that the ventricular AM levels are upregulated in both the volume- and pressure-overloaded cardiac hypertrophy by differential transcriptional regulation and that the ventricular AM may be a biochemical marker for the volume and pressure overload to the ventricle.
Altered L-type Ca2+ channel currents in vascular smooth muscle cells from experimental diabetic rats
Authors: Wang Rui , Wu Yuejin , Tang Guanghua , Wu Lingyun , Hanna Salma Toma
Published: December 2017

Vascular complications of diabetes are associated with abnormal Ca2+ handling by vascular smooth muscle cells (SMCs) in which the alteration in L-type voltage-dependent Ca2+ channel (VDCC) currents may play an important role. In the present study, the characteristics of L-type VDCC currents in tail artery SMCs from streptozotocin-induced diabetic rats were examined. The densities, but not the voltage dependence, of L-type VDCC currents were reduced as diabetes progressed from 1 wk to 3 mo. The inhibitory effect of dibutyryl-cAMP on L-type VDCC currents was greater in diabetic SMCs than in age-matched control cells ( P < 0.01). Both the stimulatory effect of BAY K 8644 and the inhibitory effect of nifedipine on L-type VDCC currents were significantly enhanced in diabetic cells. The diabetes-related abnormalities in L-type VDCC currents were mimicked by culturing SMCs with a high concentration of glucose. Our results suggest that the properties of L-type VDCC in diabetic vascular SMCs were significantly altered, partially related to the increased L-type VDCC sensitivity to cAMP and hyperglycemia.
Neurohormones in an ovine model of compensated postinfarction left ventricular dysfunction
Authors: Rademaker Miriam T. , Cameron Vicky A. , Charles Christopher J. , Espiner Eric A. , Nicholls M. Gary , Pemberton Christopher J. , Richards A. Mark
Published: December 2017

Clinical heart failure, often the result of myocardial infarction, may be preceded by a period of compensated left ventricular impairment. There is substantial need for an experimental model that reflects this human condition. In sheep, coronary artery ligation produced consistent left ventricular anteroapical myocardial infarctions resulting in chronic (5 wk), stable hemodynamic changes compared with sham controls, including reductions in ejection fraction (51 ± 2 vs. 30 ± 5%, P < 0.001), cardiac output (6.3 ± 0.2 vs. 5.1 ± 0.2 l/min, P< 0.01), and arterial pressure (93 ± 2 vs. 79 ± 3 mmHg, P< 0.001), and increases in cardiac preload (left atrial pressure, 3.3 ± 0.1 vs. 8.3 ± 1.3 mmHg, P < 0.001). These changes were associated with acute and sustained increases in plasma concentrations of atrial natriuretic peptide (ANP; 5 wk, 11 ± 2 vs. 27 ± 5 pmol/l, P < 0.001), brain natriuretic peptide (BNP; 3 ± 0.2 vs. 11 ± 2 pmol/l, P < 0.001), and amino-terminal pro-brain natriuretic peptide (NT-BNP; 17 ± 3 vs. 42 ± 12 pmol/l, P < 0.001). Significant correlations were observed between plasma levels of the natriuretic peptides (ANP, day 7 to week 5 samples; BNP and NT-BNP, day 1 to week 5samples) and changes in left ventricular volumes and ejection fraction. In contrast, renin activity, aldosterone, catecholamines, and endothelin were not chronically elevated postinfarction and were not related to indexes of ventricular function. Coronary artery ligation in sheep produces the pathological, hemodynamic, and neurohormonal characteristics of compensated left ventricular impairment secondary to myocardial infarction. Plasma concentrations of the cardiac natriuretic peptides are sensitive markers of left ventricular dysfunction. This is a reproducible model that reflects the clinical condition and should prove suitable for investigating the pathophysiology of, and experimental therapies in, early left ventricular dysfunction.
Developmental changes in endothelium-derived vasorelaxant factors in cerebral circulation
Authors: Parfenova Helena , Massie Vaughan , Leffler Charles W.
Published: December 2017

Endothelium-derived prostanoids are predominant vasorelaxant factors in the cerebral circulation of newborn pigs in vivo, whereas in older pigs nitric oxide (NO)-mediated responses also contribute to the regulation of cerebral vascular tone. We compared the expression and activities of NO synthase and cyclooxygenase in the cerebral microcirculation of newborn and adult pigs. In adult animals, expression and activity of endothelial NO synthase in cerebral microvessels and in cultured cerebral endothelial cells is two- to threefold higher than in newborn pigs; acetylcholine and bradykinin cause a greater increase in NO production in adult pigs. Expression and activity of cyclooxygenase in cerebral microvascular endothelial cells is similar in newborn and adult pigs; acetylcholine and bradykinin stimulated dilator prostanoid production to the same degree in both age groups. Endothelial prostanoid synthesis in cerebral microvessels and cultured endothelial cells was inhibited 30–70% by NS-398, reflecting a large contribution of COX-2 in both newborn and adult animals. These data indicate that in the cerebral circulation of pigs, NO synthase is age-dependently upregulated, whereas endothelial cyclooxygenase is not altered during postnatal development.
DITPA prevents the blunted contraction-frequency relationship in myocytes from infarcted hearts
Authors: Litwin Sheldon E. , Zhang Dongfang , Roberge Phyllis , Pennock Gregory D.
Published: December 2017

Loss of the positive force-frequency relationship is a characteristic finding in failing hearts. The mechanisms of this change are not well understood. Myocardial infarction (MI) was induced in rabbits to produce left ventricular (LV) dysfunction. Beginning 1 day after MI, a subgroup of rabbits received diiodothyropropionic acid (DITPA) (3.75 mg ⋅ kg−1⋅ day−1sc) for 3 wk. We measured contractions, Ca2+transients, action potentials, and sarcoplasmic reticulum (SR) Ca2+content at different stimulation rates in single LV myocytes. The shortening-frequency relationship was markedly flattened in MI myocytes compared with control myocytes. In addition, Ca2+transients, action potentials, and contractions were prolonged. Myocytes from DITPA-treated MI rabbits had preserved inotropic responses to increased stimulation rate and normal duration of action potentials and Ca2+transients. SR Ca2+content increased significantly when stimulation rate was increased from 0.5 to 2.0 Hz in control myocytes but did not change significantly in MI myocytes. Myocytes from DITPA-treated MI rabbits had a greater frequency-dependent increase in SR Ca2+content compared with the untreated MI rabbits. Thus single myocytes from infarcted rabbit hearts have frequency-dependent abnormalities of contractility, Ca2+cycling, and action potential repolarization. The flattened contraction-frequency relationship can be partially explained by an attenuation of the normal enhancement of SR Ca2+content that occurs when stimulation rate is increased. Chronic DITPA administration after MI largely prevents the development of these abnormalities.
ATP-sensitive potassium channels may participate in the coupling of neuronal activity and cerebrovascular tone
Authors: Nguyen Thien-Son , Winn H. Richard , Janigro Damir
Published: December 2017

K+ dilate and constrict cerebral vessels in a dose-dependent fashion. Modest elevations of abluminal K+ cause vasodilatation, whereas larger extracellular K+ concentration ([K+]out) changes decrease cerebral blood flow. These dilations are believed to be mediated by opening of inward-rectifier potassium channels sensitive to Ba2+. Because BaCl2 also blocks ATP-sensitive K+ channels (KATP), we challenged K+ dilations in penetrating, resistance-size (<60 mμ) rat neocortical vessels with the KATP channel blocker glibenclamide (1 μM). Glibenclamide reduced K+ responses from 138 ± 8 to 110 ± 0.8%. K+ constrictions were not affected by glibenclamide. The Na+-K+-pump inhibitor ouabain (200 μM) did not significantly change resting vessel diameter but decreased K+ dilations (from 153 ± 9 to 99 ± 2%). BaCl2 blocked K+dilations with a half-maximal dissociation constant of 2.9 μM and reduced dilations to the specific KATP agonist pinacidil with equal potency. We conclude that, in resistance vessels, K+ dilations are mediated by KATP; we hypothesize that [K+]out causes activation of Na+-K+ pumps, depletion of intracellular ATP concentration, and subsequent opening of KATP. This latter hypothesis is supported by the blocking effect of ouabain.
Action potential propagation in inhomogeneous cardiac tissue: safety factor considerations and ionic mechanism
Authors: Wang Yan , Rudy Yoram
Published: December 2017

Heterogeneity of myocardial structure and membrane excitability is accentuated by pathology and remodeling. In this study, a detailed model of the ventricular myocyte in a multicellular fiber was used to compute a location-dependent quantitative measure of conduction (safety factor, SF) and to determine the kinetics and contribution of sodium current ( I Na) and L-type calcium current [ I Ca(L)] during conduction. We obtained the following results. 1) SF decreases sharply for propagation into regions of increased electrical load (tissue expansion, increased gap junction coupling, reduced excitability, hyperkalemia); it can be <1 locally (a value indicating conduction failure) and can recover beyond the transition region to resume propagation. 2) SF and propagation across inhomogeneities involve major contribution from I Ca(L). 3) Modulating I Na or I Ca(L) (by blocking agents or calcium overload) can cause unidirectional block in the inhomogeneous region. 4) Structural inhomogeneity causes local augmentation of I Ca(L) and suppression of I Na in a feedback fashion. 5) Propagation across regions of suppressed I Na is achieved via a I Ca(L)-dependent mechanism. 6) Reduced intercellular coupling can effectively compensate for reduced SF caused by tissue expansion but not by reduced membrane excitability.
Left ventricular torsion is equal in mice and humans
Authors: Henson R. E. , Song S. K. , Pastorek J. S. , Ackerman J. J. H. , Lorenz C. H.
Published: December 2017

Global cardiac function has been studied in small animals with methods such as echocardiography, cine-magnetic resonance imaging (MRI), and cardiac catheterization. However, these modalities make little impact on delineation of pathophysiology at the tissue level. The advantage of tagged cine-MRI technique is that the twisting motion of the ventricle, referred to as torsion, can be measured noninvasively, reflecting the underlying shearing motion of individual planes of myofibrils that generate wall thickening and ventricular ejection. Thus we sought to determine whether the mechanism of ventricular ejection, as measured by torsion, was the same in both humans and mice. Nine mice and ten healthy humans were studied with tagged cine-MRI. The magnitude and systolic time course of ventricular torsion were equivalent in mouse and humans, when normalized for heart rate and ventricular length. The end-systolic torsion angle was 12.7 ± 1.7° in humans vs. 2.0 ± 1.5° in mice unnormalized and 1.9 ± 0.3°/cm vs. 2.7 ± 2.3°/cm when normalized for ventricular length). These results support the premise that ventricular torsion may be a uniform measure of normal ventricular ejection across mammalian species and heart sizes.
Nitric oxide-induced cardioprotection in cultured rat ventricular myocytes
Authors: Rakhit Roby D. , Edwards Richard J. , Mockridge James W. , Baydoun Anwar R. , Wyatt Amanda W. , Mann G. E. , Marber Michael S.
Published: December 2017

The aim of this study was to investigate the role of nitric oxide (NO) in a cellular model of early preconditioning (PC) in cultured neonatal rat ventricular myocytes. Cardiomyocytes “preconditioned” with 90 min of stimulated ischemia (SI) followed by 30 min reoxygenation in normal culture conditions were protected against subsequent 6 h of SI. PC was blocked by NG-monomethyl-l-arginine monoacetate but not by dexamethasone pretreatment. Inducible nitric oxide synthase (NOS) protein expression was not detected during PC ischemia. Pretreatment (90 min) with the NO donor S-nitroso- N-acetyl-l,l-penicillamine (SNAP) mimicked PC, resulting in significant protection. SNAP-triggered protection was completely abolished by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) but was unaffected by chelerythrine or the presence of glibenclamide and 5-hydroxydecanoate. With the use of RIA, SNAP treatment increased cGMP levels, which were blocked by ODQ. Hence, NO is implicated as a trigger in this model of early PC via activation of a constitutive NOS isoform. After exposure to SNAP, the mechanism of cardioprotection is cGMP dependent but independent of protein kinase C or ATP-sensitive K+channels. This differs from the proposed mechanism of NO-induced cardioprotection in late PC.
Detection of low- and high-frequency rhythms in the variability of skin sympathetic nerve activity
Authors: Cogliati Chiara , Magatelli Renata , Montano Nicola , Narkiewicz Krzysztof , Somers Virend K.
Published: December 2017

Spectral analysis of skin blood flow has demonstrated low-frequency (LF, 0.03–0.15 Hz) and high-frequency (HF, 0.15–0.40 Hz) oscillations, similar to oscillations in R-R interval, systolic pressure, and muscle sympathetic nerve activity (MSNA). It is not known whether the oscillatory profile of skin blood flow is secondary to oscillations in arterial pressure or to oscillations in skin sympathetic nerve activity (SSNA). MSNA and SSNA differ markedly with regard to control mechanisms and morphology. MSNA contains vasoconstrictor fibers directed to muscle vasculature, closely regulated by baroreceptors. SSNA contains both vasomotor and sudomotor fibers, differentially responding to arousals and thermal stimuli. Nevertheless, MSNA and SSNA share certain common characteristics. We tested the hypothesis that LF and HF oscillatory components are evident in SSNA, similar to the oscillatory components present in MSNA. We studied 18 healthy normal subjects and obtained sequential measurements of MSNA and SSNA from the peroneal nerve during supine rest. Measurements were also obtained of the electrocardiogram, beat-by-beat blood pressure (Finapres), and respiration. Spectral analysis showed LF and HF oscillations in MSNA, coherent with similar oscillations in both R-R interval and systolic pressure. The HF oscillation of MSNA was coherent with respiration. Similarly, LF and HF spectral components were evident in SSNA variability, coherent with corresponding variability components of R-R interval and systolic pressure. HF oscillations of SSNA were coherent with respiration. Thus our data suggest that these oscillations may be fundamental characteristics shared by MSNA and SSNA, possibly reflecting common central mechanisms regulating sympathetic outflows subserving different regions and functions.
Contractile and relaxing reactivity in carotid and femoral arteries of chicken embryos
Authors: le Noble Ferdinand A. C. , Ruijtenbeek Karin , Gommers Susanne , de Mey Jo G. R. , Blanco Carlos E.
Published: December 2017

In the embryo, hypoxemia causes redistribution of cardiac output from the periphery toward the heart and the brain. In view of this, we investigated developmental changes in the contractile and relaxing properties of the peripheral femoral artery (Fem) and the more central carotid artery (Car) at 0.7, 0.8, and 0.9 of the chicken embryo incubation time. Isolated arteries were studied in myographs and were exposed to norepinephrine or phenylephrine. High K+ (125 mM) and electrical field stimulation (0.25–16 Hz) were used to induce receptor-independent and neurogenic contractions. Relaxing responses to ACh were evaluated in the absence and presence of the nitric oxide (NO) synthase inhibitor N G-nitro-l-arginine methyl ester (l-NAME) and before and after endothelium removal. α1-Adrenergic contractile responses increased in a time-dependent manner and were significantly larger in Fem than in Car. Neurogenic contractions and adrenergic nerves could only be demonstrated in Fem at 0.9 incubation. ACh caused relaxation in both Fem and Car at 0.7, 0.8, and 0.9 incubation. The NO-independent part of the relaxation was more pronounced in Car than in Fem at all developmental stages. We conclude that the chicken embryo is a useful model to investigate the development of vasomotor control and vascular heterogeneity. The observed regional vascular differences may contribute to cardiac output redistribution during hypoxia in the embryo and might result from endothelial and neurogenic influences on vascular smooth muscle differentiation.
Force-velocity relationship and biochemical-to-mechanical energy conversion by the sarcomere
Authors: Landesberg Amir , Sideman Samuel
Published: December 2017

The intracellular control mechanism leading to the well-known linear relationship between energy consumption by the sarcomere and the generated mechanical energy is analyzed here by coupling calcium kinetics with cross-bridge cycling. A key element in the control of the biochemical-to-mechanical energy conversion is the effect of filament sliding velocity on cross-bridge cycling. Our earlier studies have established the existence of a negative mechanical feedback mechanism whereby the rate of cross-bridge turnover from the strong, force-generating conformation to the weak, non-force-generating conformation is a linear function of the filament sliding velocity. This feedback allows the analytic derivation of the experimentally established Hill's equation for the force-velocity relationship. Moreover, it allows us to derive the transient length response to load clamps and the transient force response to sarcomere shortening at constant velocity. The results are in agreement with experimental studies. The mechanical feedback regulates the generated power, maintains the linear relationship between energy liberated by the actomyosin-ATPase and the generated mechanical energy, and determines the efficiency of biochemical-to-mechanical energy conversion. The mechanical feedback defines three elements of the mechanical energy: 1) external work done; 2) pseudopotential energy, required for cross-bridge recruitment; and 3) energy dissipation caused by the viscoelastic property of the cross bridge. The last two elements dissipate as heat.
Altered membrane proteins and permeability correlate with cardiac dysfunction in cardiomyopathic hamsters
Authors: Ikeda Yasuhiro , Martone Maryann , Gu Yusu , Hoshijima Masahiko , Thor Andrea , Oh Sam S. , Peterson Kirk L. , Ross John
Published: December 2017

A mutation in the δ-sarcoglycan (SG) gene with absence of δ-SG protein in the heart has been identified in the BIO14.6 cardiomyopathic (CM) hamster, but how the defective gene leads to myocardial degeneration and dysfunction is unknown. We correlated left ventricular (LV) function with increased sarcolemmal membrane permeability and investigated the LV distribution of the dystrophin-dystroglycan complex in BIO14.6 CM hamsters. On echocardiography at 5 wk of age, the CM hamsters showed a mildly enlarged diastolic dimension (LVDD) with decreased LV percent fractional shortening (%FS), and at 9 wk further enlargement of LVDD with reduction of %FS was observed. The percent area of myocardium exhibiting increased membrane permeability or membrane rupture, assessed by Evans blue dye (EBD) staining and wheat germ agglutinin, was greater at 9 than at 5 wk. In areas not stained by EBD, immunostaining of dystrophin was detected in CM hamsters at sarcolemma and T tubules, as expected, but it was also abnormally expressed at the intercalated discs; in addition, the expression of β-dystroglycan was significantly reduced compared with control hearts. As previously described, α-SG was completely deficient in CM hearts compared with control hearts. In myocardial areas showing increased sarcolemmal permeability, neither dystrophin nor β-dystroglycan could be identified by immunolabeling. Thus, together with the known loss of δ-SG and other SGs, abnormal distribution of dystrophin and reduction of β-dystroglycan are associated with increased sarcolemmal permeability followed by cell rupture, which correlates with early progressive cardiac dysfunction in the BIO14.6 CM hamster.
Right ventricular pressure and dilation during pressure overload determine dysfunction after pressure overload
Authors: Greyson Clifford , Xu Ya , Lu Li , Schwartz Gregory G.
Published: December 2017

Volume expansion and inotropic stimulation are used clinically to augment cardiac output during acute right ventricular (RV) pressure overload. We previously showed that a brief period of RV pressure overload causes RV free wall dysfunction that persists after normal loading conditions have been restored. However, the impact of volume expansion and inotropic stimulation on the severity of RV dysfunction after acute pressure overload is unknown. We hypothesized that the severity of RV dysfunction after RV pressure overload would be related to the level of RV free wall systolic stress during RV pressure overload, rather than to the specific interventions used to augment RV function. Chloralose-anesthetized, open-chest pigs were subjected to 1 h of RV pressure overload caused by pulmonary artery constriction, followed by 1 h of recovery after release of pulmonary artery constriction. A wide range of RV free wall systolic stress during RV pressure overload was achieved by either closing or opening the pericardium (to simulate volume expansion) and by administering or not administering dobutamine. The severity of RV free wall dysfunction 1 h after RV pressure overload was strongly and directly correlated with the values of two hemodynamic variables during RV pressure overload: RV free wall area at peak RV systolic pressure (determined by sonomicrometry) and peak RV systolic pressure, two of the major determinants of peak RV free wall systolic stress. Opening or closing the pericardium, and using or not using dobutamine during RV pressure overload, had no independent effects on the severity of RV dysfunction. The findings suggest that the goal of therapeutic intervention during RV pressure overload should be to achieve the required augmentation of cardiac output with the smallest possible increase in RV free wall systolic stress.
Role of matrix metalloproteinase-2 in thrombin-induced vasorelaxation of rat mesenteric arteries
Authors: Fernandez-Patron Carlos , Radomski Marek W. , Davidge Sandra T.
Published: December 2017

The vasodilator effects of thrombin depend on activation of proteinase-activated receptor (PAR)-1 and the subsequent release of endothelin (ET)-1, which stimulates the generation of nitric oxide and PGs. We recently showed that thrombin released matrix metalloproteinase-2 (MMP-2) from rat arteries. We have now studied the significance of this release for the vasodilator effects of thrombin. Thrombin (≥100 pmol), but not a PAR-1-activating peptide (TFLLR-NH2), produced a long-lasting (>10 min) vasorelaxation of rat mesenteric arteries, as detected by a microperfusion bioassay. Thrombin induced a simultaneous release of vascular MMP-2 into arterial perfusates, as revealed by zymography. Interestingly, the vasodilator effects of thrombin were inhibited by a tissue inhibitor of MMP-2 (TIMP-2, 10 pmol). Moreover, infusion of exogenous MMP-2 (5 pmol) resulted in vasorelaxation. These vasodilatory effects of thrombin and MMP-2 were significantly ( P < 0.05) inhibited by endothelium denudation and by PD-142893 (2 nmol), an antagonist of ET receptors. Furthermore, both thrombin and MMP-2 constricted endothelium-denuded arteries. These results show that the vasodilator effects of thrombin may depend, in part, on a release of vascular MMP-2 and downstream activation of ETs. Thus MMP-2-dependent signaling may complement the PAR-1-dependent pathway of vasodilator action of thrombin.
Energetics of rat papillary muscle during contractions with sinusoidal length changes
Authors: Baxi J. , Barclay C. J. , Gibbs C. L.
Published: December 2017

The mechanical efficiency of rat cardiac muscle was determined using a contraction protocol involving cyclical, sinusoidal length changes and phasic stimulation at physiological frequencies (1–4 Hz). Experiments were performed in vitro (27°C) using rat left ventricular papillary muscles. Efficiency was determined from measurements of the net work performed and enthalpy produced by muscles during a series of 40 contractions. Net mechanical efficiency was defined as the percentage of the total, suprabasal enthalpy output that appeared as mechanical work. Maximum efficiency was ∼15% at contraction frequencies between 2 and 2.5 Hz. At lower and higher frequencies, efficiency was ∼10%. Enthalpy output per cycle was independent of cycle frequency at all but the highest frequency used. The basis of the high efficiency between 2 and 2.5 Hz was that work output was also greatest at these frequencies. At these frequencies, the duration of the applied length change was well matched to the kinetics of force generation, and active force generation occurred throughout the shortening period.
Cardiac output increases independently of basal metabolic rate in early human pregnancy
Authors: Spaanderman M. E. A. , Meertens M. , van Bussel M. , Ekhart T. H. A. , Peeters L. L. H.
Published: December 2017

Early pregnancy is characterized by the institution of a high-flow low-resistance circulation. In this study, we tested the hypothesis that these hemodynamic changes develop independently of changes in basal metabolic rate. In 12 healthy women, we determined and calculated once during the follicular phase ( day 5 ± 2) and at 6, 8, 10, and 12 wk of pregnancy the following variables: body weight and length, body mass index, fat-free mass (FFM), mean arterial pressure (MAP), heart rate (HR), stroke volume, cardiac output (CO), total peripheral vascular resistance (TPVR), resting energy expenditure (REE), FFM REE (REEFFM), and respiratory quotient (RQ). At 6 wk of gestational age, HR and CO had increased, whereas MAP and TPVR had decreased. These changes persisted throughout the study period. Meanwhile, REE, REEFFM, RQ, FFM, and body weight did not change consistently. The changes with pregnancy in hemodynamics did not correlate with those in basal metabolic rate. In early pregnancy, the institution of a high-flow low-resistance circulation develops without a concomitant rise in basal metabolic rate. These findings support the concept that the hemodynamic changes in early pregnancy develop independently of concomitant changes in basal metabolic rate.
Thrombin induces endothelin expression in arterial smooth muscle cells
Authors: Lepailleur-Enouf Delphine , Valdenaire Olivier , Philippe Monique , Jandrot-Perrus Martine , Michel Jean-Baptiste
Published: December 2017

Thrombin has been shown to stimulate endothelin release by endothelial cells, but the ability of thrombin to induce endothelin in nonendothelial cells is less well-known. Incubation of rat aortic smooth muscle cells with thrombin resulted in a stimulation of preproendothelin-1 (preproET-1) mRNA expression. This induction of preproET-1 mRNA expression by thrombin was accompanied by the release of immunoreactive peptide ET-1 into the extracellular medium. The synthetic thrombin receptor activator peptide (TRAP) confirmed ligand-specific receptor action to induce preproET-1 mRNA. Nuclear run-on analysis revealed that the transcriptional rate of preproET-1 mRNA increases twofold after 1 h of incubation with thrombin. In cells treated with thrombin, the half-life of preproET-1 mRNA was identical to that in untreated control cells. These results demonstrated that thrombin regulates endothelin synthesis at a transcriptional level but does not influence mRNA stability. Inhibition of protein kinase C (PKC) with selective inhibitors (chelerythrine and bisindolylmaleimide I) before thrombin stimulation failed to significantly inhibit preproET-1 gene expression. Inhibition of mitogen-activated protein (MAP) kinase kinase and protein tyrosine kinase decreased preproET-1 mRNA expression in thrombin-stimulated smooth muscle cells. Furthermore, addition of an activator of peroxisome proliferator-activated receptors-α (PPARα), fenofibrate, prevented the preproET-1 gene induction in response to thrombin. These results demonstrated that thrombin-induced endothelin gene transcription involved MAP kinase kinase rather than the PKC cascade in smooth muscle cells, which was repressed by PPARα stimulation.
Heme oxygenase modulates selectin expression in different regional vascular beds
Authors: Vachharajani Tushar J. , Work Jack , Issekutz Andrew C. , Granger D. Neil
Published: December 2017

Heme oxygenase (HO) catalyzes the degradation of heme to biliverdin, iron, and CO. The inducible isoform (HO-1) has been implicated as a modulator of the inflammatory response. HO-1 activity can be induced by hemin and inhibited with zinc protoporphyrin IX (ZnPP). Using these reagents, we assessed the possibility that HO-1 modulates the inflammatory response by altering the expression of endothelial cell adhesion molecules. Endotoxin (lipopolysaccharide, LPS)-induced expression of P- and E-selectin expression was quantified in different vascular beds of the rat using the dual radiolabeled monoclonal antibody technique. Pretreatment with hemin attenuated, whereas ZnPP treatment exacerbated, the increased selectin expression normally elicited by LPS. Biliverdin, at an equimolar dosage, was as effective as hemin in attenuating LPS-induced selectin expression in the lung, kidneys, liver, and intestines. These findings indicate that the anti-inflammatory properties of HO-1 may be related to an inhibitory action of P- and E-selectin expression in the vasculature. Biliverdin (or its metabolite, bilirubin), rather than CO, may account for this action of HO-1 on endothelial cell adhesion molecule expression.
Role of endogenous nitric oxide in progression of atherosclerosis in apolipoprotein E-deficient mice
Authors: Kauser Katalin , da Cunha Valdeci , Fitch Richard , Mallari Cornell , Rubanyi Gabor M.
Published: December 2017

This study investigated the role of endogenous nitric oxide (NO) in the progression of atherosclerosis in apolipoprotein E-deficient [apoE-knockout (KO)] mice. Mice were treated with N ω-nitro-l-arginine methyl ester (l-NAME) an inhibitor of nitric oxide synthase (NOS) or with the NOS substrate l-arginine for 8 wk.l-NAME treatment resulted in a significant inhibition of NO-mediated vascular responses and a significant increase in the atherosclerotic plaque/surface area in the aorta of apoE-KO mice.l-arginine treatment had no influence on endothelial function and did not alter lesion size. Mean arterial blood pressure and serum lipid levels were not altered by the treatments. At the beginning of the study impairment in endothelial function was only apparent in the case of N G-nitro-l-arginine-induced, NO-mediated contraction, whereas ACh-induced, NO-mediated relaxation was not different between age-matched apoE-KO and C57Bl/6J mice. After the 8-wk treatment with the NOS inhibitor, both NO-mediated responses were significantly inhibited. The acceleration in lesion size concomitant to the severely impaired NO-mediated responses indicates that lack of endogenous NO is an important progression factor of atherosclerosis in the apoE-KO mouse.
Gene transfer of dominant negative Rho kinase suppresses neointimal formation after balloon injury in pigs
Authors: Eto Yasuhiro , Shimokawa Hiroaki , Hiroki Junko , Morishige Kunio , Kandabashi Tadashi , Matsumoto Yasuharu , Amano Mutsuki , Hoshijima Masahiko , Kaibuchi Kozo , Takeshita Akira
Published: December 2017

Restenosis after angioplasty still remains a major problem for which neointimal formation appears to play an important role. Recent studies in vitro suggested that Rho kinase, a target protein of Rho, is important in various cellular functions. We thus examined whether Rho kinase is involved in the restenotic changes after balloon injury. In vivo gene transfer was performed immediately after balloon injury in both sides of the porcine femoral arteries with adenoviral vector encoding either a dominant negative form of Rho kinase (AdDNRhoK) or β-galactosidase (AdLacZ) as a control. One week after the transfer, immunohistochemistry confirmed the successful gene expression in the vessel wall, whereas 2 wk after the transfer, Western blotting showed the functional upregulation of Rho kinase at the AdLacZ site and its suppression at the AdDNRhoK site. Angiography showed the development of a stenotic lesion at the AdLacZ site where histological neointimal formation was noted, whereas those changes were significantly suppressed at the AdDNRhoK site. These results indicate that Rho kinase is involved in the pathogenesis of neointimal formation after balloon injury in vivo.