bluuebunny/crossref_metadata_2025 huggingface dataset:
A new integrative method to quantify total Ca2+handling and futile Ca2+cycling in failing hearts
Authors: Shimizu Juichiro , Araki Junichi , Mizuno Ju , Lee Shinyu , Syuu Yi , Hosogi Shingo , Mohri Satoshi , Mikane Takeshi , Takaki Miyako , Taylor Tad W. , Suga Hiroyuki
Published: December 2017

Ca2+handling in excitation-contraction coupling requires considerable O2consumption (Vo2) in cardiac contraction. We have developed an integrative method to quantify total Ca2+handling in normal hearts. However, its direct application to failing hearts, where futile Ca2+cycling via the Ca2+-leaky sarcoplasmic reticulum (SR) required an increased Ca2+handling Vo2, was not legitimate. To quantify total Ca2+handling even in such failing hearts, we combined futile Ca2+cycling with Ca2+handling Vo2and the internal Ca2+recirculation fraction via the SR. We applied this method to the canine heart mechanoenergetics before and after intracoronary ryanodine at nanomolar concentrations. We found that total Ca2+handling per beat was halved after the ryanodine treatment from ∼60 μmol/kg left ventricle before ryanodine. We also found that futile Ca2+cycling via the SR increased to >1 cycle/beat after ryanodine from presumably zero before ryanodine. These results support the applicability of the present method to the failing hearts with futile Ca2+cycling via the SR.
Low-frequency component of the heart rate variability spectrum: a poor marker of sympathetic activity
Authors: Houle Melanie S. , Billman George E.
Published: December 2017

The low-frequency component of the heart rate variability spectrum (0.06–0.10 Hz) is often used as an accurate reflection of sympathetic activity. Therefore, interventions that enhance cardiac sympathetic drive, e.g., exercise and myocardial ischemia, should elicit increases in the low-frequency power. Furthermore, because an enhanced sympathetic activation has been linked to an increased propensity for malignant arrhythmias, one might also predict a greater low-frequency power in animals that are susceptible to ventricular fibrillation than in resistant animals. To test these hypotheses, a 2-min coronary occlusion was made during the last minute of exercise in 71 dogs with healed myocardial infarctions: 43 had ventricular fibrillation (susceptible) and 28 did not experience arrhythmias (resistant). Exercise or ischemia alone provoked significant heart rate increases in both groups of animals, with the largest increase in the susceptible animals. These heart rate increases were attenuated by β-adrenergic receptor blockade. Despite the sympathetically mediated increases in heart rate, the low-frequency power decreased, rather than increased, in both groups, with the largest decrease again in the susceptible animals: 4.0 ± 0.2 (susceptible) vs. 4.1 ± 0.2 ln ms2 (resistant) in preexercise control and 2.2 ± 0.2 (susceptible) vs. 2.9 ± 0.2 ln ms2 (resistant) at highest exercise level. In a similar manner the parasympathetic antagonist atropine sulfate elicited significant reductions in the low-frequency power. Although sympathetic nerve activity was not directly recorded, these data suggest that the low-frequency component of the heart rate power spectrum probably results from an interaction of the sympathetic and parasympathetic nervous systems and, as such, does not accurately reflect changes in the sympathetic activity.
Influence of glutathione peroxidase on coronary artery responses to alterations in Po2and H2O2
Authors: Mohazzab-H. Kamal M. , Agarwal Ritu , Wolin Michael S.
Published: December 2017

Our previous work suggests that relaxation of endothelium-removed bovine coronary arteries (BCA) to posthypoxic reoxygenation is mediated by NADH oxidase-dependent superoxide anion-derived H2O2and cGMP. The purpose of this study was to investigate if altering BCA GSH peroxidase activity by enhancing its activity with a GSH peroxidase-mimetic (0.1 mM Ebselen) or by inhibiting its activity with an inhibitor of GSH peroxidase [10 mM mercaptosuccinic acid (MS)] causes a selective modulation of responses to exogenously (1 μM–1 mM H2O2) and endogenously generated (reoxygenation and 1–10 mM lactate) H2O2. Ebselen inhibited and MS enhanced all of the responses that are thought to be mediated by H2O2, without having significant effects on relaxation to hypoxia or a nitric oxide donor [1 nM–10 μM S-nitroso- N-acetylpenicillamine (SNAP)]. Thus enhancement of BCA GSH peroxidase activity with Ebselen inhibits relaxation to reoxygenation, lactate, and H2O2, whereas inhibition of GSH peroxidase with MS causes potentiation of responses thought to be mediated by H2O2in BCA. Inactivation of catalase by pretreatment of BCA with 3-amino-1,2,4-triazole (50 mM, 30 min) inhibited relaxation to H2O2and the potentiation by MS. Whereas the actions of these probes are not consistent with a role for oxidation of GSH in the relaxation to H2O2, their effects are potentially a result of modulating the metabolism of H2O2by endogenous catalase, which is thought to mediate the stimulation of the cytosolic or soluble form of guanylate cyclase.
Blood pressure and heart rate in the ovine fetus: ontogenic changes and effects of fetal adrenalectomy
Authors: Unno Nobuya , Wong Chi H. , Jenkins Susan L. , Wentworth Richard A. , Ding Xiu-Ying , Li Cun , Robertson Steven S. , Smotherman William P. , Nathanielsz Peter W.
Published: December 2017

Ontogenic changes in baseline and 24-h rhythms of fetal arterial blood pressure (FABP) and heart rate (FHR) and their regulation by the fetal adrenal were studied in 18 fetal sheep chronically instrumented at 109–114 days gestation (GA). In the long-term study, FABP and FHR were continuously recorded from 120 days GA to spontaneous term labor (>145 days GA) in five animals. Peak times (PT) and amplitudes (Amp) of cosinor analysis were compared at 120–126, 127–133, and 134–140 days GA. Consistent, significant linear increases in FABP and linear decreases in FHR were observed in all fetuses. Significant 24-h rhythms in FABP and FHR were observed during all the time windows. In the adrenalectomy study, to test the hypothesis that fetal cortisol plays a key role in cardiovascular maturation, fetal adrenals were removed in eight animals (ADX); sham fetal adrenalectomy was performed on five animals (Con). Cortisol (4 μg/min) was infused intravenously in four ADX fetuses from day 7postsurgery for 7 days (ADX+F). No significant changes in PT and Amp in FABP and FHR were observed. Plasma cortisol levels remained low in Con and ADX fetuses (<4.9 ng/ml). Cortisol infusion increased fetal plasma cortisol to 22.3 ± 3.2 ng/ml (mean ± SE) on day 13 in ADX+F fetuses. FABP increased in control and ADX+F but not ADX fetuses; FHR decreased in control and ADX but rose in ADX+F fetuses. These results suggest that, in chronically instrumented fetal sheep at late gestation, 1) increases in FABP and decreases in FHR are maintained consistently from 120 to 140 days GA, with distinct 24-h rhythms, the PT and Amp of which remain unchanged, and 2) the physiological increase in FABP is dependent on the fetal adrenal; bilateral removal of the fetal adrenals does not prevent the ability of cortisol to produce a sustained increase in FABP.
Modulation of Ca2+ transient decay by tension and Ca2+removal in hyperthyroid myocardium
Authors: Ishikawa Tetsuya , Kajiwara Hidetoshi , Kurihara Satoshi
Published: December 2017

We investigated the contribution of sarcoplasmic reticulum (SR) and Na+/Ca2+exchanger in the tension-dependent change in the decay of the Ca2+ transients (CaT) in euthyroid (Eu) and hyperthyroid (Hy) myocardium. Hy was induced by thyroxine treatment to enhance the rate of SR Ca2+ uptake. With the use of the aequorin method, CaT and tension in twitch contraction were simultaneously measured under various conditions (changing muscle length and Ca2+ concentration in solution). In both groups, the decay time of CaT (DT) showed a significant dependence on the developed tension, but the tension dependence of DT in Hy was significantly less than in Eu. In the presence of caffeine (3 mM), the tension dependence of DT in Hy became apparent as in Eu. Inhibition of Na+/Ca2+exchanger by replacing Na+ with Li+ did not affect the dependence in Hy. The normalized extra Ca2+, which is the Ca2+ concentration change in response to a quick length change, in Hy was similar to that in Eu. pCa-tension relations of skinned trabeculae measured at different lengths (1.9 and 2.3 μm) were nearly identical in both groups. These results indicate that the tension-dependent change in the affinity of troponin C for Ca2+works in both Eu and Hy myocardium and that the tension-dependent change in DT is influenced by the Ca2+ uptake rate of SR.
SERCA1a can functionally substitute for SERCA2a in the heart
Authors: Ji Yong , Loukianov Evgeny , Loukianova Tanya , Jones Larry R. , Periasamy Muthu
Published: December 2017

We recently generated a transgenic (TG) mouse model in which the fast-twitch skeletal muscle sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA1a) is overexpressed in the heart. Ectopic overexpression of SERCA1a results in remodeling of the cardiac SR containing 80% SERCA1a and 20% endogenous SERCA2a with an ∼2.5-fold increase in the total amount of SERCA protein (E. Loukianov et al. Circ. Res. 83: 889–897, 1998). We have analyzed the Ca2+transport properties of membranes from SERCA1a TG hearts in comparison to control hearts. Our data show that the maximal velocity of SR Ca2+transport was significantly increased (∼1.9-fold) in TG hearts, whereas the apparent affinity of the SERCA pump for Ca2+was not changed. Addition of phospholamban antibody in the Ca2+uptake assays increased the apparent affinity for Ca2+to the same extent in TG and non-TG (NTG) hearts, suggesting that phospholamban regulates the SERCA1a pump in TG hearts. Analysis of SERCA enzymatic properties in TG hearts revealed that the SERCA pump affinity for ATP, the Hill coefficient, the pH dependence of Ca2+uptake, and the effect of acidic pH on Ca2+transport were similar to those of NTG hearts. Interestingly, the rate constant of phosphoenzyme decay (turnover rate of SERCA enzyme) was also very similar between TG and NTG hearts. Together these findings suggest that 1) the SERCA1a pump can functionally substitute for SERCA2a and is regulated by endogenous phospholamban in the heart and 2) SERCA1a exhibits several enzymatic properties similar to those of SERCA2a when expressed in a cardiac setting.
Surgical procedure affects physiological parameters in rat myocardial ischemia: need for mechanical ventilation
Authors: Horstick Georg , Berg Oliver , Heimann Axel , Darius Harald , Lehr Hans Anton , Bhakdi Sucharit , Kempski Oliver , Meyer Jürgen
Published: December 2017

Several surgical approaches are being used to induce myocardial ischemia in rats. The present study investigated two different operative procedures in spontaneously breathing and mechanically ventilated rats under sham conditions. A snare around the left coronary artery (LCA) was achieved without occlusion. Left lateral thoracotomy was performed in spontaneously breathing and mechanically ventilated rats (tidal volume 8 ml/kg) with a respiratory rate of 90 strokes/min at different levels of O2 supplementation (room air and 30, 40, and 90% O2). All animals were observed for 60 min after thoracotomy. Rats operated with exteriorization of the heart through left lateral thoracotomy while breathing spontaneously developed severe hypoxia and hypercapnia despite an intrathoracic operation time of <1 min. Arterial O2 content decreased from 18.7 ± 0.5 to 3.3 ± 0.9 vol%. Lactate increased from 1.2 ± 0.1 to 5.2 ± 0.3 mmol/l. Significant signs of ischemia were seen in the electrocardiogram up to 60 min. Mechanically ventilated animals exhibited a spectrum ranging from hypoxia (room air) to hyperoxia (90% O2). In order not to jeopardize findings in experimental myocardial ischemia-reperfusion injury models, stable physiological parameters can be achieved in mechanically ventilated rats at an O2application of 30–40% at 90 strokes/min.
Ca2+-independent inhibition of myocardial contraction by coronary effluent of hypoxic rat hearts
Authors: Yang Zhao-Kang , Draper Nick J. , Shah Ajay M.
Published: December 2017

Endothelial cells release agents that influence cardiac contraction. We recently reported that cultured hypoxic endothelial cells release an unidentified factor(s) that inhibits myocardial contraction. In this study, we investigated the effects of coronary effluent of isolated hypoxic rat hearts on isolated rat ventricular myocyte contraction. Coronary effluent collected during brief moderate hypoxia significantly depressed myocyte twitch shortening and decreased diastolic length, with only minor reduction in intracellular Ca2+transients. These effects were similar to those of hypoxic rat coronary microvascular endothelial cell superfusates and were reversed by reoxygenation of hearts. “Hypoxic” coronary effluent exerted essentially Ca2+-independent effects on myofilament interaction in intact myocytes, as assessed by 1) peak Ca2+-shortening relations, 2) phase-plane analysis of instantaneous Ca2+-cell length relations, and 3) “steady-state” myofilament responses in tetanized, sarcoplasmic reticulum-disabled cells. Thus an unidentified substance(s) that inhibits myocyte shortening predominantly via effects on the myofilaments is reversibly released during acute moderate hypoxia of isolated hearts, presumably from coronary endothelial cells. Release of such an agent may be relevant to the cardiac contractile response to hypoxia.
Exercise-induced expression of angiogenesis-related transcription and growth factors in human skeletal muscle
Authors: Gustafsson Thomas , Puntschart Adrian , Kaijser Lennart , Jansson Eva , Sundberg Carl Johan
Published: December 2017

mRNA expression of vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF-2), and hypoxia-inducible factor (HIF) subunits HIF-1α and HIF-1β in human skeletal muscle was studied during endurance exercise at different degrees of oxygen delivery. Muscle biopsies were taken before and after 45 min of one-legged knee-extension exercise performed under conditions of nonrestricted or restricted blood flow (∼15–20% lower) at the same absolute workload. Exercise increased VEGF mRNA expression by 178% and HIF-1β by 340%, but not HIF-1α and FGF-2. No significant differences between the restricted and nonrestricted groups were observed. The exercise-induced increase in VEGF mRNA was correlated to the exercise changes in HIF-1α and HIF-1β mRNA. The changes in VEGF, HIF-1α, and HIF-1β mRNAs were correlated to the exercise-induced increase in femoral venous plasma lactate concentration. It is concluded that 1) VEGF but not FGF-2 gene expression is upregulated in human skeletal muscle by a single bout of dynamic exercise and that there is a graded response in VEGF mRNA expression related to the metabolic stress and 2) the increase in VEGF mRNA expression correlates to the changes in both HIF-1α and HIF-1β mRNA.
Endothelin antagonists block α1-adrenergic constriction of coronary arterioles
Authors: DeFily David V. , Nishikawa Yasuhiro , Chilian William M.
Published: December 2017

We have previously observed that intracoronary administration of the α1-adrenergic agonist phenylephrine (PE) over a period of minutes induced both an immediate and long-lasting (2 h) vasoconstriction of epicardial coronary arterioles. Because it is unlikely that α1-adrenergic constriction would persist for hours after removal of the agonist, this observation supports the view that another constrictor(s) is released during α1-adrenergic activation and induces the prolonged vasoconstriction. Therefore, we hypothesized that the prolonged microvascular constriction after PE is due to the production of endothelin (ET). We focused on ET not only because this peptide produces potent vasoconstriction but also because its vasoconstrictor action is characterized by a long duration. To test this hypothesis, the diameters of coronary arterioles (<222 μm) in the beating heart of pentobarbital-anesthetized dogs with stroboscopic intravital microscopy were measured during a 15-min intracoronary infusion of PE (1 μg ⋅ kg−1⋅ min−1) and at 15-min intervals for a total of 120 min. All experiments were performed in the presence of β-adrenergic blockade with propranolol. At 120 min, arterioles in the PE group were constricted (−23 ± 9% change in diameter vs. baseline). Pretreatment with the ET-converting enzyme inhibitor phosphoramidon or the ETA-receptor antagonist FR-139317 prevented the PE-induced constriction at 120 min (−1 ± 3 and −6 ± 3%, respectively, P < 0.01 vs. PE). Pretreatment with the selective α1-adrenergic antagonist prazosin (Prz) also prevented the sustained constriction (0 ± 2%, P < 0.01 vs. PE) but Prz given 60 min after PE infusion did not (−13 ± 3%). In the aggregate, these results show that vasoconstriction of epicardial coronary arterioles via α1-adrenergic activation is blocked by an ET antagonist and an inhibitor of its production. From these data, we conclude that α1-adrenergic activation promotes the production and/or release of ET, which produces or facilitates microvascular constriction of epicardial canine coronary arterioles.
Inhibition of NO synthesis or endothelium removal reveals a vasoconstrictor effect of insulin on isolated arterioles
Authors: Schroeder C. Andrew , Chen Ya-Li , Messina Edward J.
Published: December 2017

In this study we tested the hypothesis that insulin may differentially affect isolated arterioles from red (RGM) and white gastrocnemius muscles (WGM) because of their differences in function and metabolic profile. We also determined whether the responses of these arterioles are endothelium dependent and mediated by either prostaglandins or nitric oxide (NO). Arterioles were isolated, pressurized to 85 mmHg, equilibrated in Krebs bicarbonate-buffered solution (pH 7.4) gassed with 10% O2 (5% CO2-85% N2), and studied in a no-flow state. Control diameters for first-order arterioles from RGM averaged 77 ± 8 μm and from WGM averaged 77 ± 5 μm. Cumulative dose-response curves to insulin (10 μU/ml, 100 μU/ml, 1 mU/ml, and 10 mU/ml) were obtained in arterioles before and after endothelium removal or administration of either indomethacin (Indo, 10−5 M) or N G-nitro-l-arginine (l-NNA, 10−4 M). Insulin evoked concentration-dependent increases in control diameter of intact RGM and WGM arterioles of 6–26% and 9–28%, respectively. Indo was without any effect on insulin-induced dilation in RGM and WGM arterioles. Insulin-evoked dilation in both RGM and WGM arterioles was completely inhibited and converted to vasoconstriction by endothelium removal and administration of l-NNA. These results indicate that in endothelium-intact arterioles from RGM and WGM, insulin evokes an endothelium-dependent dilation that is equivalent and mediated by NO. In contrast, in the absence of a functional endothelium, insulin evokes arteriolar constriction. The finding that insulin can constrict arterioles, at physiological concentrations, suggests that insulin may play a more significant role in the regulation of vascular tone and total peripheral resistance than previously appreciated.
Normal pregnancy is associated with enhanced endothelium-dependent flow-mediated vasodilation
Authors: Dørup Inge , Skajaa Kristjar , Sørensen Keld E.
Published: December 2017

Normal pregnancy is characterized by reduced systemic vascular resistance, which may be mediated by nitric oxide (NO). We compared endothelial vasomotor function in 71 normal pregnant women (13 in first, 29 in middle, and 29 in last trimester) to 37 healthy age-matched controls. With external ultrasound, brachial artery diameter was measured at rest, during reactive hyperemia [with increased flow causing endothelium-dependent dilation (FMD)], and after sublingual nitroglycerin (causing endothelium-independent dilation). Compared with controls, resting flow and brachial artery diameter were significantly higher during the middle and last trimesters. Reactive hyperemia was reduced in all pregnant groups. FMD increased from the first trimester (by 26%), reaching the highest value in the last trimester (to 47% above nonpregnant values). FMD was significantly correlated to pregnancy status (nonpregnant or pregnant) and to vessel size. Nitroglycerin-induced dilation was similar in pregnant and nonpregnant women. A longitudinal study of eight women evaluated in the first, middle, and last trimesters confirmed an increase in FMD throughout pregnancy. The study supports the idea that basal and stimulated NO activity is enhanced in normal pregnancy and may contribute to the decrease in peripheral resistance.
Gender differences in coronary artery diameter reflect changes in both endothelial Ca2+and ecNOS activity
Authors: Knot Harm J. , Lounsbury Karen M. , Brayden Joseph E. , Nelson Mark T.
Published: December 2017

Elevation of nitric oxide (NO) release from the vascular endothelium may contribute to some of the gender-associated differences in coronary artery function. The mechanisms by which gender affects NO release from the endothelium of coronary arteries are not known. In this study, endothelial function was examined in pressurized coronary arteries from female and male rats. Diameter and endothelial cell intracellular Ca2+concentration ([Ca2+]i) in intact arteries, as well as enzymatic activity of endothelial constitutive nitric oxide synthase (ecNOS) in arterial lysates, was measured. Elevation of intravascular pressure to 60 mmHg constricted coronary arteries from female animals less than coronary arteries from male animals (18% and 31% constriction, respectively). The increased arterial diameter of coronary arteries from females was associated with elevated endothelial [Ca2+]i(female 174 nM, male 90 nM; P < 0.001). Elevation of Ca2+activated ecNOS with a similar slope and half-activation constant (∼160 nM) for both female and male coronary arteries. However, at [Ca2+] > 100 nM, ecNOS activity was significantly higher in coronary arteries from female rats compared with their male equivalents ( P < 0.01). Maximal activity for ecNOS at saturating Ca2+(300 nM) was 37% higher in coronary arteries from female animals compared with male animals ( P < 0.05). Thus elevated [Ca2+]iin the endothelium of female coronary arteries alone is predicted to increase the production of NO (by nearly 2-fold). This gender difference combined with increased ecNOS activity at a given [Ca2+] in females indicates that tonic NO production should be nearly threefold greater in female coronary arteries compared with male coronary arteries. We conclude that, in the regulation of endothelial Ca2+and ecNOS, gender differences contribute significantly to the overall decrease in myogenic tone observed in coronary arteries of females.
Cortical NOS inhibition raises the lower limit of cerebral blood flow-arterial pressure autoregulation
Authors: Jones Stephen C. , Radinsky Carol R. , Furlan Anthony J. , Chyatte Douglas , Perez-Trepichio Alejandro D.
Published: December 2017

The maintenance of constant cerebral blood flow (CBF) as arterial blood pressure is reduced, commonly referred to as CBF-pressure autoregulation, is typically characterized by a plateau until the vasodilatory capacity is exhausted at the lower limit, after which flow falls linearly with pressure. We investigated the effect of cortical, as opposed to systemic, nitric oxide synthase (NOS) inhibition on the lower limit of CBF-pressure autoregulation. Forty-four Sprague-Dawley rats were anesthetized with halothane and N2O in O2. With a closed cranial window placed the previous day in a ventilated and physiologically stable preparation, we determined the CBF using laser-Doppler flowmetry. Animals with low reactivity to inhaled CO2 and suffused ADP or ACh were excluded. Five arterial pressures from 100 to 40 mmHg were obtained with controlled hemorrhagic hypotension under cortical suffusion with artificial cerebrospinal fluid (aCSF) and then again after suffusion for 35 ( n = 5) and 105 min ( n = 10) with aCSF, 10−3 M N ω-nitro-l-arginine (l-NNA; n = 12), or 10−3 M N ω-nitro-d-arginine (d-NNA; n = 5). An additional group ( n = 7) was studied after a 105-min suffusion of l-NNA followed by a single blood withdrawal procedure. The lower limit of autoregulation was identified visually by four blinded reviewers as a change in the slope of the five-point plot of CBF vs. mean arterial blood pressure. The lower limit of 90 ± 4.3 mmHg after 105 min of 1 mMl-NNA suffusion was increased compared with the value in the time-control group of 75 ± 5.3 mmHg ( P < 0.01; ANOVA) and the initial value of 67 ± 3.7 mmHg ( P < 0.001). The lower limit of 84 ± 5.9 mmHg in seven animals with 105 min of suffusion of 1 mM l-NNA without previous blood withdrawal was significantly increased ( P < 0.01) in comparison with 70 ± 1.9 mmHg from those with just aCSF suffusion ( n = 37). No changes in lower limit for the other agents or conditions, including 105 or 35 min of aCSF or 35 min of l-NNA suffusion, were detected. The lack of effect on the lower limit withd-NNA suffusion suggests an enzymatic mechanism, and the lengthyl-NNA exposure of 105 min, but not 35 min, suggests inhibition of a diffusionally distant NOS source that mediates autoregulation. Thus cortical suffusion ofl-NNA raises the lower limit of autoregulation, strongly suggesting that nitric oxide is at least one of the vasodilators active during hypotension as arterial pressure is reduced from normal.
Oxygen-wasting effect of inotropy  in the “virtual work model”
Authors: Korvald Christian , Elvenes Odd P. , Ytrebø Lars M. , Sørlie Dag G. , Myrmel Truls
Published: December 2017

In the “virtual work model,” left ventricular total mechanical energy (TME) is linearly related to myocardial oxygen consumption (MV˙o2). This relationship (MV˙o2-TME) is supposedly independent of inotropic stimulation, vascular loading, and heart rate variations. We reexamined the effect of inotropic stimulation (dopamine) on the metabolic to mechanical energy transfer in nine open-chest anesthetized pigs. Left ventricular mechanical energy was calculated using TME (mean ejection pressure × end-diastolic volume + stroke work), TMEW(end-diastolic volume reduced by unstressed ventricular volume), and the pressure-volume area (PVA). A highly linear relationship between MV˙o2and mechanical energy was found for all three indexes during control and dopamine runs ( r = 0.87–0.99). The slopes were unaltered by dopamine. y-Axis intercepts were (control vs. dopamine) as follows (in J ⋅ beat−1⋅ 100 mg−1; means ± SD): TME, 0.36 ± 0.12 vs. 0.61 ± 0.30 ( P< 0.02); TMEW, 0.43 ± 0.16 vs. 0.72 ± 0.32 ( P < 0.02); and PVA, 0.34 ± 0.13 vs. 0.60 ± 0.30 ( P < 0.02). We conclude that the virtual work model is dependent on inotropic stimulation and that new insight into myocardial chemomechanical coupling is not added by this concept.
Impaired aerobic capacity in hypercholesterolemic mice: partial reversal by exercise training
Authors: Niebauer Josef , Maxwell Andrew J. , Lin Patrick S. , Tsao Philip S. , Kosek Jon , Bernstein Daniel , Cooke John P.
Published: December 2017

The present study assessed whether impaired aerobic capacity previously observed in hypercholesterolemic mice is reversible by exercise training. Seventy-two 8-wk-old female C57BL/6J wild-type (+, n = 42) and apolipoprotein E-deficient (−, n = 30) mice were assigned to the following eight interventions: normal chow, sedentary (E+, n = 17; E−, n = 8) or exercised ([Formula: see text], n= 13; [Formula: see text], n = 7) and high-fat chow, sedentary ([Formula: see text], n = 6;[Formula: see text], n = 8) or exercised ([Formula: see text], n = 6;[Formula: see text], n = 7). Mice were trained on a treadmill 2 × 1 h/day, 6 days/wk, for 4 wk. Cholesterol levels correlated inversely with maximum oxygen uptake ( r = −0.35; P < 0.02), which was blunted in all hypercholesterolemic sedentary groups (all P < 0.05). Maximum oxygen uptake improved in all training groups but failed to match[Formula: see text] (all P< 0.05). Vascular reactivity and nitric oxide (NO) synthesis correlated with anaerobic threshold ( r = 0.36; P < 0.025) and maximal distance run ( r = 0.59; P < 0.007). We conclude that genetically induced hypercholesterolemia impairs aerobic capacity. This adverse impact of hypercholesterolemia on aerobic capacity may be related to its impairment of vascular NO synthesis and/or vascular smooth muscle sensitivity to nitrovasodilators. Aerobic capacity is improved to the same degree by exercise training in normal and genetically hypercholesterolemic mice, although there remains a persistent difference between these groups after training.
Role of adenosine in local metabolic coronary vasodilation
Authors: Yada Toyotaka , Richmond Keith Neu , van Bibber Richard , Kroll Keith , Feigl Eric O.
Published: December 2017

Adenosine has been postulated to mediate the increase in coronary blood flow when myocardial oxygen consumption is increased. The aim of this study was to evaluate the role of adenosine when myocardial oxygen consumption was augmented by cardiac paired-pulse stimulation without the use of catecholamines. In 10 anesthetized closed-chest dogs, coronary blood flow was measured in the left circumflex coronary artery, and myocardial oxygen consumption was calculated using the arteriovenous oxygen difference. Cardiac interstitial adenosine concentration was estimated from coronary venous and arterial plasma adenosine measurements using a previously described multicompartmental, axially distributed mathematical model. Paired stimulation increased heart rate from 55 to 120 beats/min, increased myocardial oxygen consumption 104%, and increased coronary blood flow 92%, but the estimated interstitial adenosine concentration remained below the threshold for coronary vasodilation. After adenosine-receptor blockade with 8-phenyltheophylline (8-PT), coronary blood flow and myocardial oxygen consumption were not significantly different from control values. Paired-pulse pacing during adenosine-receptor blockade resulted in increases in myocardial oxygen consumption and coronary blood flow similar to the response before 8-PT. Coronary venous and estimated interstitial adenosine concentration did not increase to overcome the adenosine blockade by 8-PT. These results demonstrate that adenosine is not required for the local metabolic control of coronary blood flow during pacing-induced increases in myocardial oxygen consumption.
Changes in intracellular Na+and pH in rat heart during ischemia: role of Na+/H+exchanger
Authors: Park Choon-Ok , Xiao Xiao-Hui , Allen David G.
Published: December 2017

The role of the Na+/H+exchanger in rat hearts during ischemia and reperfusion was investigated by measurements of intracellular Na+concentration ([Na+]i) and intracellular and extracellular pH. Under our standard conditions (2-Hz stimulation), 10 min of ischemia caused no significant rise in [Na+]ibut an acidosis of 1.0 pH unit, suggesting that the Na+/H+exchanger was inactive during ischemia. This was confirmed by showing that the Na+/H+exchange inhibitor methylisobutyl amiloride (MIA) had no effect on [Na+]ior on intracellular pH during ischemia. However, there was a short-lived increase in [Na+]iof 8.2 ± 0.6 mM on reperfusion, which was reduced by MIA, showing that the Na+/H+exchanger became active on reperfusion. To investigate the role of metabolic changes, we measured [Na+]iduring anoxia. The [Na+]idid not change during 10 min of anoxia, but there was a small, transient rise of [Na+]ion reoxygenation, which was inhibited by MIA. In addition, we show that the Na+/H+exchanger, tested by sodium lactate exposure, was inhibited during anoxia. These results show that the Na+/H+exchanger is inhibited during ischemia and anoxia, probably by an intracellular metabolic mechanism. The exchanger activates rapidly on reperfusion and can cause a rapid rise in [Na+]i.
Mechanisms of desensitization to a PDE inhibitor (milrinone) in conscious dogs with heart failure
Authors: Sato Naoki , Asai Kuniya , Okumura Satoshi , Takagi Gen , Shannon Richard P. , Fujita-Yamaguchi Yoko , Ishikawa Yoshihiro , Vatner Stephen F. , Vatner Dorothy E.
Published: December 2017

The goal of this study was to determine the extent to which the effects of milrinone were desensitized in heart failure (HF) and to determine the mechanisms, i.e., whether these effects could be ascribed to changes in cAMP or phosphodiesterase (PDE) activity in HF. Accordingly, we examined the effects of milrinone in seven conscious dogs before and after HF was induced by rapid ventricular pacing at 240 beats/min. The dogs were chronically instrumented for measurements of left ventricular (LV) pressure and first derivative of LV pressure (dP/d t), arterial pressure, LV internal diameter, and wall thickness. Milrinone (10 μg ⋅ kg−1 ⋅ min−1iv) increased LV dP/d t by 1,854 ± 157 from 2,701 ± 105 mmHg/s ( P < 0.05) before HF. After HF the increase in LV dP/d t in response to milrinone was attenuated significantly ( P < 0.05); it increased by 615 ± 67 from 1,550 ± 107 mmHg/s, indicating marked desensitization. In the presence of ganglionic blockade the increases in LV dP/d t (+445 ± 65 mmHg/s) in response to milrinone were markedly less ( P < 0.01), and milrinone increased LV dP/d t even less in HF (+240 ± 65 mmHg/s). cAMP and PDE activity were measured in endocardial and epicardial layers in normal and failing myocardium. cAMP was decreased significantly ( P < 0.05) in LV endocardium (−26%) but not significantly in LV epicardium (−14%). PDE activity was also decreased significantly ( P < 0.05) in LV endocardium (−18%) but not in LV epicardium (−4%). Thus significant desensitization to milrinone was observed in conscious dogs with HF. The major effect was autonomically mediated. The biochemical mechanism appears to be due in part to the modest reductions in PDE activity in failing myocardium, which, in turn, may be a compensatory mechanism to maintain cAMP levels in HF. Reductions in cAMP and PDE levels were restricted to the subendocardium, suggesting that the increased wall stress and reduced coronary reserve play a role in mediating these changes.
Effect of 17β-estradiol in hypercholesterolemic rabbits with severe endothelial dysfunction
Authors: Nascimento Carlos Antonio Do , Kauser Katalin , Rubanyi Gabor M.
Published: December 2017

17β-Estradiol prevents early vascular lesion development and may also affect advanced atherosclerosis. To test the antiatherosclerotic effect of estrogen under conditions that resemble more advanced human atherosclerosis with severe endothelial dysfunction, we have investigated the effect of 17β-estradiol in hypercholesterolemic rabbits treated with the nitric oxide synthase inhibitor N ω-nitro-l-arginine methyl ester (l-NAME). Chronicl-NAME administration attenuated endothelial nitric oxide (EDNO)-mediated vascular responses leading to significantly accelerated atherosclerotic plaque development. 17β-Estradiol treatment alone inhibited aortic lesion formation with concurrent increase in EDNO-mediated responses. The beneficial effect of estrogen persisted in thel-NAME-treated rabbits, suggesting that the antiatherogenic action of 17β-estradiol involves NO-independent mechanisms as well. Serum cholesterol levels were not altered by any of the treatments. 17β-Estradiol treatment significantly increased EDNO production under these conditions as well. The reduction in plaque size by 17β-estradiol was always accompanied by increased EDNO production, suggesting a strong association between these two events. The results demonstrate that estrogen treatment may exert protection against atherosclerosis even in patients with severe endothelial dysfunction.
Systemic arterial compliance is reduced in young patients with IDDM
Authors: Berry Karen L. , Skyrme-Jones R. Andrew P. , Cameron James D. , O’Brien Richard C. , Meredith Ian T.
Published: December 2017

Arterial elastic properties are altered with increasing age and in various disease states, including non-insulin-dependent diabetes mellitus (NIDDM). Whether young patients with insulin-dependent diabetes mellitus (IDDM) have reduced arterial compliance before developing endothelial dysfunction or overt micro- and macrovascular disease is unclear. Systemic arterial compliance and endothelium-dependent, flow-mediated vasodilation (FMD) was assessed in 25 individuals with uncomplicated IDDM (23 ± 4 yr, 14 females and 11 males) and compared with 30 age-matched controls (15 females and 15 males). Arterial compliance was determined via simultaneous measurements of aortic blood flow and carotid arterial pressure. The relationship between arterial compliance and endothelial function (assessed by brachial artery FMD) was also examined. Arterial compliance was 29% lower in IDDM subjects compared with control subjects (0.46 ± 0.05 vs. 0.65 ± 0.07 arbitrary compliance units, P < 0.05). Blood pressure, lipid levels, and daily energy expenditure (a measure of physical activity levels) were not different between groups. Compliance in the IDDM group was not related to the integrity of endothelial vasodilator function, disease duration, or degree of glycemic control. Arterial compliance is reduced in young patients with IDDM before the development of overt micro- or macrovascular disease. Early assessment of arterial compliance may be useful in predicting the development of diabetic vascular complications.
Cardioprotective effects of KB-R7943: a novel inhibitor of the reverse mode of Na+/Ca2+exchanger
Authors: Ladilov Y. , Haffner S. , Balser-Schäfer C. , Maxeiner H. , Piper H. M.
Published: December 2017

The novel inhibitor of the reverse mode of the Na+/Ca2+exchanger (NCE) KB-R7943 (KB) was tested in isolated rat cardiomyocytes exposed to 80 min of simulated ischemia [substrate-free anoxia, extracellular pH (pHo) of 6.4] and 15 min of reoxygenation (pHo7.4). At pHo6.4, 20 μmol/l KB was required for complete inhibition of the reverse mode of NCE. Treatment with 20 μmol/l KB only during anoxia did not influence the onset of rigor contracture and intracellular pH (pHi) (monitored with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein) but significantly reduced the cytosolic accumulation of Ca2+(monitored with fura 2) and Na+(monitored with sodium-binding benzofuran isophthalate). During reoxygenation, cardiomyocytes developed hypercontracture. This was significantly reduced by anoxic KB treatment. To investigate this protection against reoxygenation-induced injury in the whole heart, we exposed Langendorff-perfused rat hearts to 110 min of anoxia (pHo6.4) and 50 min of reoxygenation (pHo7.4). Application of 20 μmol/l KB during anoxia significantly reduced the reoxygenation-induced enzyme release. We conclude that KB offers significant protection of cardiomyocytes against Ca2+and Na+overload during anoxia and hypercontracture or enzyme release on reoxygenation.
End-systolic myocardial stiffness is a load-independent index of contractility in stage 24 chick embryonic heart
Authors: Tobita Kimimasa , Keller Bradley B.
Published: December 2017

Cardiac morphogenesis and function are interrelated during cardiovascular development. We evaluated the effects of acute alteration of loading condition to chick embryonic ventricular contractility using end-systolic myocardial stiffness based on the incremental elastic modulus concept. End-systolic stress-strain relations including geometric factor and end-systolic myocardial stiffness were determined from the simultaneous measurement of ventricular pressure and chamber dimension in the following four groups of stage 24 White Leghorn chick embryos: volume infusion ( n = 9), conotruncal occlusion ( n = 9), calcium suffusion ( n = 10), and verapamil suffusion ( n = 8). The end-systolic stress-strain relationship was linear in each embryo. There was no correlation between end-systolic myocardial stiffness and end-systolic stress. End-systolic myocardial stiffness increased with calcium suffusion ( P < 0.05 vs. volume infusion). The geometric factor increased after verapamil suffusion ( P < 0.05). End-systolic myocardial stiffness normalized by geometric factor was not changed by alteration of preload or afterload, increased after calcium suffusion, and decreased after verapamil administration ( P < 0.05). These results suggest that normalized end-systolic myocardial stiffness is a load-independent index of ventricular contractility in the developing embryonic chick ventricle.
PDGF-A expression correlates with blood pressure and remodeling in 1K1C hypertensive rat arteries
Authors: Dobrian Anca , Wade Suzanne S. , Prewitt Russell L.
Published: December 2017

We previously demonstrated remodeling of large and small arteries in angiotensin II-treated rats, paralleled by an increased expression of platelet-derived growth factor (PDGF)-A chain mRNA in large arteries. Both remodeling and PDGF-A expression were associated with elevation of blood pressure rather than a direct effect of angiotensin II. To further delineate the role of PDGF-A and elevated blood pressure, we assessed the level of PDGF-A and -B mRNA and protein in the wall of large as well as small arteries in the one-kidney, one-clip (1K1C) hypertensive rat, a non-renin-dependent model of hypertension. Fourteen days after renal artery stenosis, the thoracic aorta and both femoral arteries were collected from 1K1C rats ( n = 8) and uninephrectomized controls ( n = 8) and immediately processed for morphological measurement, immunohistochemistry, RT-PCR, and Western blotting. Systolic blood pressure was significantly elevated in hypertensive rats (202 ± 26 mmHg) compared with control rats (122 ± 7.9 mmHg) and was accompanied by arterial hypertrophy in both aorta and femoral arteries. The mRNA for PDGF-A chain was increased threefold in the thoracic aorta ( P < 0.05) of 1K1C rats, whereas the message for PDGF-B was not significantly changed in hypertensive versus control animals. A higher staining of the intima-media was observed by using an anti-PDGF-A chain polyclonal antibody on paraffin-embedded sections. Western blot results indicated an ∼2-fold increase in PDGF-A protein in aortic and femoral wall of the 1K1C rats. The results showed that both the mRNA and protein for PDGF-A chain are increased and well correlated with the blood pressure and wall area, suggesting a direct effect of elevated pressure on PDGF synthesis, which, in turn, may affect the onset and progression of vascular hypertrophy.
Microvascular endothelial cells remodel cultured adult cardiomyocytes and increase their survival
Authors: Kubin Thomas , Ando Hiroshi , Scholz Dimitri , Bramlage Peter , Kostin Sawa , van Veen Antonius , Heling Annette , Hein Stefan , Fischer Silvia , Breier Albert , Schaper Jutta , Schaper Wolfgang
Published: December 2017

We investigated the paracrine effect of cardiac microvascular endothelial cells (MVEC) on cultured adult rat cardiomyocytes (ARC). ARC were exposed for 8 days to serum-free medium (CM) conditioned by MVEC. Controls were grown in FCS or FCS-free medium. Protein synthesis of CM-stimulated ARC increased twofold versus 5% FCS-stimulated cells until day 8. Seventy-nine percent of CM-treated myocytes survived, whereas only twenty-four percent of FCS-free ARC retained viability. The phenotype of myocytes exposed to CM was different from control. Analysis by confocal laser microscopy of CM-stimulated myocytes showed actin staining throughout the whole cell body up to the peripheral extensions, with concomitant appearance of myomesin in a cross-striated pattern. The reexpression of fetal α-smooth muscle actin determined immunohistochemically and by Western blot increased from day 6 in CM-treated cells, whereas ARC grown in up to 20% serum were negative. These effects could not be mimicked by any of the other cardioactive substances tested here, indicating a novel trophic factor in CM.
Parasympathetic modulation of sinoatrial node pacemaker activity in rabbit heart: a unifying model
Authors: Demir Semahat S. , Clark John W. , Giles Wayne R.
Published: December 2017

We have extended our compartmental model [ Am. J. Physiol. 266 ( Cell Physiol. 35): C832–C852, 1994] of the single rabbit sinoatrial node (SAN) cell so that it can simulate cellular responses to bath applications of ACh and isoprenaline as well as the effects of neuronally released ACh. The model employs three different types of muscarinic receptors to explain the variety of responses observed in mammalian cardiac pacemaking cells subjected to vagal stimulation. The response of greatest interest is the ACh-sensitive change in cycle length that is not accompanied by a change in action potential duration or repolarization or hyperpolarization of the maximum diastolic potential. In this case, an ACh-sensitive K+ current is not involved. Membrane hyperpolarization occurs in response to much higher levels of vagal stimulation, and this response is also mimicked by the model. Here, an ACh-sensitive K+ current is involved. The well-known phase-resetting response of the SAN cell to single and periodically applied vagal bursts of impulses is also simulated in the presence and absence of the β-agonist isoprenaline. Finally, the responses of the SAN cell to longer continuous trains of periodic vagal stimulation are simulated, and this can result in the complete cessation of pacemaking. Therefore, this model is 1) applicable over the full range of intensity and pattern of vagal input and 2) can offer biophysically based explanations for many of the phenomena associated with the autonomic control of cardiac pacemaking.
ANG II- and TxA2-induced mesenteric vasoconstriction in rats is mediated by separate cell signaling pathways
Authors: Bauer Johannes , Dau Cécile , Cavarape Alessandro , Schaefer Franz , Ehmke Heimo , Parekh Niranjan
Published: December 2017

Studies in vitro have demonstrated that vasoconstrictor agents increase intracellular Ca2+and activate protein kinase C (PKC) to elevate vascular tone. The aim of the present study was to determine the importance of these signaling pathways for angiotensin II (ANG II) and thromboxane A2(TxA2) in regulating mesenteric blood flow (MBF) in vivo. In anesthetized rats increasing doses of ANG II or the TxA2agonist U-46619 were administered into the superior mesenteric artery to reduce MBF. Intra-arterial infusion of inhibitors served to examine the contribution of different pathways: 8-(diethylamino)octyl 3,4,5-trimethoxybenoate hydrochloride (TMB-8) to inhibit intracellular Ca2+release, nifedipine to block transmembrane Ca2+influx through the L-type Ca2+channel, and staurosporine to inhibit PKC. Each of the inhibitors attenuated ANG II-induced reductions in MBF, and all dose-response curves were shifted to the right to an approximately threefold higher ANG II dose. Combinations of the inhibitors revealed that their effects were additive; together they abolished the vasoconstrictor action of ANG II completely. In contrast, the dose-response curve for U-46619 was not affected by any of the inhibitors infused either separately or together. The results demonstrate that a rise in intracellular Ca2+and activation of PKC are major mediators of the vasoconstrictor effect of ANG II in mesenteric circulation, but they play a subordinate role, if any, for the effects of TxA2. Because TxA2plays a major role only under pathological conditions, the uncontrolled vasoconstriction appears to be associated with the recruitment of novel signal transduction pathways.