bluuebunny/crossref_metadata_2025 huggingface dataset:
β-Adrenergic stimulation induces transient imbalance between myocardial substrate uptake and metabolism in vivo
Authors: Xu Ya , Lu Li , Zhu Peili , Schwartz Gregory G.
Published: December 2017

At steady state, a balance is expected between net myocardial uptake of the principal exogenous carbon substrates and the rate at which these substrates are metabolized. Such a balance is present when the sum of the oxygen extraction ratios (OERs) for glucose, lactate, and free fatty acids (FFA) is near unity. We have previously observed that systemic administration of the β-adrenergic agonist isoproterenol (Iso) induces a state of excess myocardial substrate uptake relative to the rate of substrate metabolism, reflected by a sum of OERs significantly >1.0. This occurs in conjunction with an Iso-stimulated increase in circulating insulin levels. The goal of the present study was to determine whether this excess substrate uptake depends on the effects of insulin and time. In open-chest anesthetized pigs, myocardial blood flow, substrate uptake, and oxygen consumption were measured at baseline and during systemic administration of Iso (0.08 μg ⋅ kg−1⋅ min−1iv) under the following conditions: group 1 ( n = 10), normal endogenous insulin release; group 2( n = 10), inhibition of endogenous insulin release with somatostatin; group 3 ( n = 7), at 45 and 90 min Iso; group 4( n = 7), at 45 and 90 min Iso, with exogenous insulin given during the latter measurement. In group 1, plasma insulin rose fivefold with Iso while the sum of the OERs for glucose, lactate, and FFA increased from 0.92 ± 0.21 at baseline to 1.57 ± 0.17 with Iso ( P < 0.01). In group 2, somatostatin blunted the increase in insulin with Iso and there was no significant change in the sum of OERs between baseline and Iso. In group 3, the sum of OERs increased from 0.95 ± 0.11 at baseline to 1.69 ± 0.20 at 45 min Iso ( P < 0.01), similar to the response of group 1. However, the state of excess substrate uptake was transient; by 90 min Iso the sum of OERs declined to 0.69 ± 0.21 ( P < 0.05 vs. 45 min Iso). In group 4, excess substrate uptake could not be sustained at 90 min Iso despite administration of exogenous insulin. Systemic β-adrenergic stimulation causes a transient condition of myocardial substrate uptake in excess of metabolism. Increased plasma insulin is necessary to produce this condition, but a high insulin level does not prolong the condition.
NO modulates P-selectin and ICAM-1 mRNA expression and hemodynamic alterations in hepatic I/R
Authors: Liu Peitan , Xu Baohuan , Hock Carl E. , Nagele Robert , Sun Frank F. , Wong Patrick Y-K
Published: December 2017

The anti-inflammatory role of nitric oxide (NO) was studied in a model of hepatic ischemia-reperfusion (I/R) in rats. Male Fischer rats were subjected to 30 min of no-flow ischemia of the left and median lobes of the liver, and animals were examined for a 4-h period of reperfusion. The animals were divided into the following groups: control-vehicle; I/R-vehicle; I/R- N ω-nitro-l-arginine methyl ester (l-NAME, 10 mg/kg iv, 10 min before reperfusion); sham control-l-NAME, and I/R- S-nitroso- N-acetyl-penicillamine (SNAP, 25 μmol/kg iv, 10 min before reperfusion, followed by 20 μmol ⋅ kg−1 ⋅ h−1in 1.0 ml saline infused for 4 h). Results showed that mean arterial blood pressure was significantly increased in the sham control-l-NAME or I/R-l-NAME groups compared with either the I/R-vehicle or I/R-SNAP groups. However, cardiac index (CI) and stroke volume index (SVI) were markedly decreased, and systemic vascular resistance index (SVRI) was dramatically increased. Interestingly, the CI and SVI in rats treated with SNAP were markedly improved over that of the I/R group. Plasma nitrate and nitrite levels were significantly decreased in the I/R-l-NAME group; however, superoxide generation in the ischemic lobes and plasma alanine aminotransferase activity were higher compared with I/R-SNAP rats. Thel-NAME-induced enhancement of hepatic injury in rats with I/R may be due in part to neutrophil infiltration, which was significantly increased compared with animals subjected to I/R or I/R-SNAP. The mechanism ofl-NAME-enhanced neutrophil infiltration may be due to the fact that the ratios of P-selectin and intercellular adhesion molecule 1 (ICAM-1) mRNA to glyceraldehyde-3-phosphate dehydrogenase mRNA extracted from the ischemic lobes of I/R-l-NAME rats were significantly increased when compared with the I/R-SNAP group. These results suggest that 1) endogenous NO reduces the SVRI and permits an increased CI and SVI; 2) exogenous NO further improves CI and SVI; and 3) endogenous, but not exogenous, NO decreases P-selectin and ICAM-1 mRNA expression, thereby reducing polymorphonuclear neutrophil-dependent reperfusion tissue injury.
Mechanism of prejunctional muscarinic receptor-mediated inhibition of neurogenic vasodilation in cerebral arteries
Authors: Liu J. , Lee T. J. F.
Published: December 2017

Nitric oxide (NO) is a major transmitter in mediating cerebral neurogenic vasodilation in several species. Recent findings have suggested that acetylcholine, which is costored with NO in cerebral perivascular nerves, plays a role in modulating NO release, presumably by acting on muscarinic (M) receptors on nitric oxidergic nerve terminals. The present study was designed using an in vitro tissue bath technique to pharmacologically characterize the presynaptic muscarinic-receptor subtype(s) that mediate modulation of NO release and therefore neurogenic vasodilation and to investigate further the possible mechanisms involved in this presynaptic modulation in porcine basilar arteries. Transmural nerve stimulation (TNS) elicited a frequency-dependent, tetrodotoxin-sensitive relaxation. The relaxation was abolished by nitro-l-arginine (30 μM) and was completely reversed byl-arginine andl-citrulline, but not by their d-enantiomers. Atropine (0.01–1 μM), pirenzepine (an M1-receptor antagonist, 0.01–1 μM), and methoctramine (an M2-receptor antagonist, 0.01–1 μM), but not 4-DAMP (an M3-receptor antagonist) or tropicamide (an M4-receptor antagonist) at concentrations as high as 10 mM, significantly increased the TNS-elicited relaxation. This relaxation, on the other hand, was significantly attenuated by arecaidine but-2-ynyl ester tosylate (an M2-receptor agonist, 0.1 μM) but was not affected by McN-A-343 (an M1-receptor agonist, 1 μM). Double-labeling immunohistochemical study demonstrated that perivascular M2receptor-immunoreactive fibers were completely coincident with NADPH diaphorase fibers. Furthermore, the muscarinic receptor-mediated modulation of TNS-elicited relaxation was completely prevented by ω-conotoxin GVIA (0.1 μM), a specific N-type Ca2+channel inhibitor, but was still observed in the presence of tetraethylammonium (1 mM), 8-bromo-cAMP (0.5 mM), and pertussis toxin. It is concluded that the presynaptic M2receptors on porcine cerebral perivascular nitric oxidergic nerves mediate inhibition of NO release. The inhibition is due primarily to a decreased Ca2+influx through N-type Ca2+channels.
Total arterial inertance as the fourth element of the windkessel model
Authors: Stergiopulos Nikos , Westerhof Berend E. , Westerhof Nico
Published: December 2017

In earlier studies we found that the three-element windkessel, although an almost perfect load for isolated heart studies, does not lead to accurate estimates of total arterial compliance. To overcome this problem, we introduce an inertial term in parallel with the characteristic impedance. In seven dogs we found that ascending aortic pressure could be predicted better from aortic flow by using the four-element windkessel than by using the three-element windkessel: the root-mean-square errors and the Akaike information criterion and Schwarz criterion were smaller for the four-element windkessel. The three-element windkessel overestimated total arterial compliance compared with the values derived from the area and the pulse pressure method ( P = 0.0047, paired t-test), whereas the four-element windkessel compliance estimates were not different ( P = 0.81). The characteristic impedance was underestimated using the three-element windkessel, whereas the four-element windkessel estimation differed marginally from the averaged impedance modulus at high frequencies ( P = 0.0017 and 0.031, respectively). When applied to the human, the four-element windkessel also was more accurate in these same aspects. Using a distributed model of the systemic arterial tree, we found that the inertial term results from the proper summation of all local inertial terms, and we call it total arterial inertance. We conclude that the fourelement windkessel, with all its elements having a hemodynamic meaning, is superior to the three-element windkessel as a lumped-parameter model of the entire systemic tree or as a model for parameter estimation of vascular properties.
Arterial O2 content and tension in regulation of cardiac output and leg blood flow during exercise in humans
Authors: Roach Robert C. , Koskolou Maria D. , Calbet José A. L. , Saltin Bengt
Published: December 2017

A universal O2 sensor presumes that compensation for impaired O2delivery is triggered by low O2tension, but in humans, comparisons of compensatory responses to altered arterial O2 content ([Formula: see text]) or tension ([Formula: see text]) have not been reported. To directly compare cardiac output (Q˙TOT) and leg blood flow (LBF) responses to a range of[Formula: see text] and[Formula: see text], seven healthy young men were studied during two-legged knee extension exercise with control hemoglobin concentration ([Hb] = 144.4 ± 4 g/l) and at least 1 wk later after isovolemic hemodilution ([Hb] = 115 ± 2 g/l). On each study day, subjects exercised twice at 30 W and on to voluntary exhaustion with an[Formula: see text] of 0.21 or 0.11. The interventions resulted in two conditions with matched[Formula: see text] but markedly different [Formula: see text] (hypoxia and anemia) and two conditions with matched[Formula: see text] and different[Formula: see text] (hypoxia and anemia + hypoxia). [Formula: see text] varied from 46 ± 3 Torr in hypoxia to 95 ± 3 Torr (range 37 to >100) in anemia ( P < 0.001), yet LBF at exercise was nearly identical. However, as[Formula: see text] dropped from 190 ± 5 ml/l in control to 132 ± 2 ml/l in anemia + hypoxia ( P < 0.001),Q˙TOT and LBF at 30 W rose to 12.8 ± 0.8 and 7.2 ± 0.3 l/min, respectively, values 23 and 47% above control ( P< 0.01). Thus regulation ofQ˙TOT, LBF, and arterial O2 delivery to contracting intact human skeletal muscle is dependent for signaling primarily on[Formula: see text], not[Formula: see text]. This finding suggests that factors related to [Formula: see text]or [Hb] may play an important role in the regulation of blood flow during exercise in humans.
Influence of chronic ethanol consumption on arterial tone in young and aged rats
Authors: Kähönen Mika , Karjala Kirsi , Hutri-Kähönen Nina , Wu Xiumin , Jaatinen Pia , Riihioja Päivi , Hervonen Antti , Pörsti Ilkka
Published: December 2017

The aim of this work was to evaluate the effects of long-term ethanol consumption on arterial responses in vitro in young and aged rats. Therefore, Wistar rats (ages 3 and 29 mo, respectively) were allocated to six groups: control-young, sucrose-young, ethanol-young, control-aged, sucrose-aged, and ethanol-aged. The ethanol-fed groups were given 25% ethanol by intragastric gavage three times a day 4 days a week. Responses of mesenteric arterial rings were examined in standard organ chambers after 5 treatment weeks. In norepinephrine-precontracted arterial rings, endothelium-dependent relaxations to acetylcholine, as well as endothelium-independent relaxations to isoproterenol, were attenuated in aged rats when compared with young controls. Relaxation responses to isoproterenol, but not to acetylcholine and nitroprusside, were clearly improved by ethanol treatment in both young and aged rats. The cyclooxygenase inhibitor diclofenac, which reduces the synthesis of dilating and constricting prostanoids, enhanced the relaxation to acetylcholine in all three aged rat groups but was without significant effect in the young rats. In the presence of the nitric oxide synthase inhibitor N G-nitro-l-arginine methyl ester the relaxation to acetylcholine in control and sucrose-fed aged rats was markedly reduced compared with control rats, whereas in the young controls and in both young and aged ethanol-exposed groups, distinct relaxations to higher concentrations of acetylcholine were still present. The endothelium-independent relaxations to cromakalim, a hyperpolarizing vasodilator acting via ATP-sensitive potassium channels, were also markedly augmented by ethanol feeding in both young and aged rats. In conclusion, ethanol consumption in both young and aged rats was associated with markedly improved arterial relaxations to isoproterenol and cromakalim, as well as clearly augmented relaxation to acetylcholine during inhibition of cyclooxygenase and nitric oxide synthase. These findings suggest that especially the potassium channel-related component of arterial relaxation was augmented by long-term ethanol exposure.
Early activation of transcription factor NF-κB during ischemia in perfused rat heart
Authors: Li Chuanfu , Browder William , Kao Race L.
Published: December 2017

The transcription factor nuclear factor κB (NF-κB) regulates multiple immediate-early gene expressions involved in immune and inflammatory responses and cellular defenses. Ischemia-reperfusion induces many immediate-early gene expressions, but little is known about the NF-κB activation in myocardium during ischemia and reperfusion. This study demonstrated that ischemia alone rapidly induced NF-κB activation in the myocardium of isolated working rat hearts. Electrophoretic mobility shift assay showed that NF-κB binding activity significantly increased in the nucleus after 5 min of ischemia and remained elevated for up to 30 min. Western blot analysis suggested that the levels of inhibitory IκBα protein in the cytoplasm became markedly decreased at 4, 5, 7.5, and 10 min of ischemia but were gradually restored following 10 min of ischemia. Reduction of IκBα protein in the cytoplasm by ischemia resulted in NF-κB translocation to the nucleus. Northern blot hybridization showed that IκBα mRNA levels were not significantly elevated during myocardial ischemia. Pyrrolidine dithiocarbamate, an antioxidant, significantly inhibited the loss of IκBα protein from the cytoplasm and prevented NF-κB binding activity in the nucleus. Reperfusion following short periods of ischemia augmented NF-κB binding activity in the nucleus induced by ischemia. The results suggest that early activation of NF-κB induced by ischemia in the myocardium could be a signal mechanism for controlling and regulating immediate-early gene expression during ischemia-reperfusion.
Disparate effects of three types of extracellular acidosis on left ventricular function
Authors: Berger David S. , Fellner Susan K. , Robinson Kimberly A. , Vlasica Katherine , Godoy Ivan E. , Shroff Sanjeev G.
Published: December 2017

Effects of acidosis on muscle contractile function have been studied extensively. However, the relative effects of different types of extracellular acidosis on left ventricular (LV) contractile function, especially the temporal features of contraction, have not been investigated in a single model. We constituted perfusion buffers of identical ionic composition, including Ca2+concentration ([Ca2+]), to mimic physiological control condition (pH 7.40) and three types of acidosis with pH of 7.03: inorganic (IA), respiratory (RA), and lactic (LA). Isolated rabbit hearts ( n = 9) were perfused with acidotic buffers chosen at random, each preceded by the control buffer. Under steady-state conditions, instantaneous LV pressure (Pv) and volume (Vv) were recorded for a range of Vv. The results were as follows. 1) LV passive (end-diastolic) elastance increased with IA and RA. However, this increase may not be a direct effect of acidosis; it can be explained on the basis of myocardial turgor. 2) Although LV inotropic state (peak active Pvand elastance) was depressed by all three acidotic buffers, the magnitude of inotropic depression was significantly less for LA. 3) Temporal features of Pvwere altered differently. Whereas IA and RA reduced time to peak Pv( tmax) and hastened isovolumic relaxation at a common level of LV wall stress, LA significantly increased tmaxand retarded relaxation. These results and a model-based interpretation suggest that cooperative feedback (i.e., force-activation interaction) plays an important role in acidosis-induced changes in LV contractile function. Furthermore, it is proposed that LA-induced responses comprise two components, one due to intracellular acidosis and the other due to pH-independent effects of lactate ions.
Conducted signals within arteriolar networks initiated by bioactive amino acids
Authors: Frame Mary D. S.
Published: December 2017

Our purpose was to determine the specificity of l-arginine (l-Arg)-induced conducted signals for intra- vs. extracellular actions ofl-Arg. Diameter and red blood cell velocities were measured for arterioles [18 ± 1.6 (SE) μm] in the cremaster muscle of pentobarbital sodium-anesthetized (Nembutal, 70 mg/kg) hamsters ( n = 53). Remote (conducted) responses were viewed ∼1,000 μm upstream from the local (micropipette) application. Six amino acids were tested:l-arginine,l-cystine,l-leucine,l-lysine,l-histidine, andl-aspartate (100 μM each). Only l-Arg induced a remote dilation; l-lysine andl-aspartate had no effect, and the others each induced a significant remote constriction. There is a second conducted signal initiated byl-arginine that preconditions the arteriolar network and upregulates a direct response ofl-arginine to dilate the remote site. This was blocked by inhibition ofl-arginine uptake at the local (preconditioning) site (100 μMl-histidine or 1 mM phenformin). Arginine-glycine-aspartate (100 μM)-induced remote dilations (+3.2 ± 0.3 μm) were not mimicked by a peptide control and were prevented by anti- integrin αv monoclonal antibody. Remote dilations were greater in animals with a higher wall shear stress for arginine-glycine-aspartate ( r 2 = 0.92) but not for l-arginine ( r 2 = 0.12). Thusl-arginine initiates separate conducted signals related to system y+ transport, integrins, and baseline flow.
Heart rate and behavior of fur seals: implications for measurement of field energetics
Authors: Boyd I. L. , Bevan R. M. , Woakes A. J. , Butler P. J.
Published: December 2017

Archival data loggers were used to collect information about depth, swimming speed, and heart rate in 23 free-ranging antarctic fur seals. Deployments averaged 9.6 ± 5.6 days (SD) and totaled 191 days of recording. Heart rate averaged 108.7 ± 17.7 beats/min (SD) but varied from 83 to 145 beats/min among animals. Morphometrics explained most variations in heart rate among animals. These interacted with diving activity and swimming speed to produce a complex relationship between heart rate and activity patterns. Heart rate was also correlated with behavior over time lags of several hours. There was significant ( P < 0.05) variation among animals in the degree of diving bradycardia. On average, heart rate declined from 100–130 beats/min before the dive to 70–100 beats/min during submersion. On the basis of the relationship between heart rate and rate of oxygen consumption, the overall metabolic rate was 5.46 ± 1.61 W/kg (SD). Energy expenditure appears to be allocated to different activities within the metabolic scope of individual animals. This highlights the possibility that some activities can be mutually exclusive of one another.
Myocardial creatine kinase kinetics in hearts with postinfarction left ventricular remodeling
Authors: Murakami Yo , Zhang Jianyi , Eijgelshoven Marcel H. J. , Chen Wei , Carlyle Wenda C. , Zhang Yi , Gong Guangrong , Bache Robert J.
Published: December 2017

This study examined whether alterations in myocardial creatine kinase (CK) kinetics and high-energy phosphate (HEP) levels occur in postinfarction left ventricular remodeling (LVR). Myocardial HEP and CK kinetics were examined in 19 pigs 6 wk after myocardial infarction was produced by left circumflex coronary artery ligation, and the results were compared with those from 9 normal pigs. Blood flow (microspheres), oxygen consumption (MV˙o2), HEP levels [31P magnetic resonance spectroscopy (MRS)], and CK kinetics (31P MRS) were measured in myocardium remote from the infarct under basal conditions and during dobutamine infusion (20 μg ⋅ kg−1⋅ min−1iv). Six of the pigs with LVR had overt congestive heart failure (CHF) at the time of study. Under basal conditions, creatine phosphate (CrP)-to-ATP ratios were lower in all transmural layers of hearts with CHF and in the subendocardium of LVR hearts than in normal hearts ( P < 0.05). Myocardial ATP (biopsy) was significantly decreased in hearts with CHF. The CK forward rate constant was lower ( P < 0.05) in the CHF group (0.21 ± 0.03 s−1) than in LVR (0.38 ± 0.04 s−1) or normal groups (0.41 ± 0.03 s−1); CK forward flux rates in CHF, LVR, and normal groups were 6.4 ± 2.3, 14.3 ± 2.1, and 20.3 ± 2.4 μmol ⋅ g−1⋅ s−1, respectively ( P < 0.05, CHF vs. LVR and LVR vs. normal). Dobutamine caused doubling of the rate-pressure product in the LVR and normal groups, whereas CHF hearts failed to respond to dobutamine. CK flux rates did not change during dobutamine in any group. The ratios of CK flux to ATP synthesis (from MV˙o2) under baseline conditions were 10.9 ± 1.2, 8.03 ± 0.9, and 3.86 ± 0.5 for normal, LVR, and CHF hearts, respectively (each P < 0.05); during dobutamine, this ratio decreased to 3.73 ± 0.5, 2.58 ± 0.4, and 2.78 ± 0.5, respectively ( P = not significant among groups). These data demonstrate that CK flux rates are decreased in hearts with postinfarction LVR, but this change does not limit the response to dobutamine. In hearts with end-stage CHF, the changes in HEP and CK flux are more marked. These changes could contribute to the decreased responsiveness of these hearts to dobutamine.
Regulation of energy consumption in cardiac muscle: analysis of isometric contractions
Authors: Landesberg Amir , Sideman Samuel
Published: December 2017

The well-known linear relationship between oxygen consumption and force-length area or the force-time integral is analyzed here for isometric contractions. The analysis, which is based on a biochemical model that couples calcium kinetics with cross-bridge cycling, indicates that the change in the number of force-generating cross bridges with the change in the sarcomere length depends on the force generated by the cross bridges. This positive-feedback phenomenon is consistent with our reported cooperativity mechanism, whereby the affinity of the troponin for calcium and, hence, cross-bridge recruitment depends on the number of force-generating cross bridges. Moreover, it is demonstrated that a model that does not include a feedback mechanism cannot describe the dependence of energy consumption on the loading conditions. The cooperativity mechanism, which has been shown to determine the force-length relationship and the related Frank-Starling law, is shown here to provide the basis for the regulation of energy consumption in the cardiac muscle.
L- and T-type voltage-gated Ca2+currents in adrenal medulla endothelial cells
Authors: Vinet Raul , Vargas Fernando F.
Published: December 2017

We investigated voltage-dependent Ca2+channels of bovine adrenal medulla endothelial cells with the whole cell version of the patch-clamp technique. Depolarization elicited an inward current that was carried by Ca2+and was composed of a transient (T) current, present in all the cells tested, and a sustained (L) current, present in 65% of them. We separated these currents and measured their individual kinetic and gating properties. The activation threshold for T current was approximately −50 mV, and its maximum amplitude was −49.8 ± 4.8 pA (means ± SE, n = 19) at 0 mV. The time constant was 10.2 ± 1.5 ms ( n= 4) for activation and 18.4 ± 2.8 ms ( n = 4) for inactivation. The L current activated at −40 mV, and it reached a plateau at −20.1 ± 2.3 pA ( n = 6). Its activation time course was a single exponential with an activation time contant of 26.8 ± 2.3 ms ( n = 4). Current-voltage curves, kinetics, gating, response to BAY K 8644, nifedipine, amiloride, and different selectivity for Ba2+and Ca2+indicated that the underlying channels for the observed currents are only of the T- and L-types that resemble those of the endocrine secretory cells.
Adenosine A2a-receptor activation enhances cardiomyocyte shortening via Ca2+-independent and -dependent mechanisms
Authors: Woodiwiss Angela J. , Honeyman Thomas W. , Fenton Richard A. , Dobson James G.
Published: December 2017

Adenosine A2areceptor (A2aR) stimulation enhances the shortening of ventricular myocytes. Whether the A2aR-mediated increase in myocyte contractility is associated with alterations in the amplitude of intracellular Ca2+transients was investigated in isolated, contracting rat ventricular myocytes using the Ca2+-sensitive fluorescent dye fura 2-AM. In the presence of intact inhibitory G protein pathways, 10−4M 2- p-(2-carboxyethyl)phenethyl-amino-5′- N-ethylcarboxamidoadenosine (CGS-21680), an A2aR agonist, insignificantly increased Ca2+transients by 8 ± 5%, whereas myocyte shortening increased by 54 ± 1%. In contrast, 2 × 10−7M isoproterenol, a β-adrenergic receptor agonist, increased Ca2+transients by 104 ± 15% and increased myocyte shortening by 61 ± 6%. When A2aR were stimulated in myocytes that had the antiadrenergic actions of adenosine (Ado) abolished by either treatment with pertussis toxin (PTx) or the presence of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), an adenosine A1-receptor antagonist, the maximum increases in Ca2+transients were similarly nominal (with PTx: 10−4M CGS-21680, 14 ± 6% and 10−4M Ado, 15 ± 4%; without PTx: 10−5M Ado + 2 × 10−7M DPCPX, 19 ± 1%). These results indicate that compared with β-adrenergic stimulation, which markedly increases myocyte Ca2+transients and shortening, A2aR-mediated increases in myocyte shortening are accompanied by only modest increases in Ca2+transients. These observations suggest that the A2aR-induced contractile effects are mediated predominantly by Ca2+-independent inotropic mechanisms.
PKC-dependent activation of p44/p42 MAPKs during myocardial ischemia-reperfusion in conscious rabbits
Authors: Ping Peipei , Zhang Jun , Cao Xinan , Li Richard C. X. , Kong Deying , Tang Xian-Liang , Qiu Yumin , Manchikalapudi Srinivas , Auchampach John A. , Black Richard G. , Bolli Roberto
Published: December 2017

Using conscious rabbits, we examined the effect of ischemic preconditioning (PC) on p44 and p42 mitogen-activated protein kinases (MAPKs). We found that both isoforms contribute significantly to total MAPK activity in the heart (in-gel kinase assay: p44, 59 ± 1%; p42, 41 ± 1%). Ischemic PC (6 cycles of 4-min occlusion/4-min reperfusion) elicited a pronounced increase in total cellular MAPK activity (+89%). This increase, which occurred exclusively in the nuclear fraction, was contributed by both isoforms (in-gel kinase assay: p44, +97%; p42, +210%) and was accompanied by migration of the two proteins from the cytosolic to the nuclear compartment. In control rabbits, MAPK kinase (MEK)1 and MEK2, direct activators of p44 and p42 MAPKs, were located almost exclusively in the cytosolic fraction. Ischemic PC induced a marked increase in cytosolic MEK activity (+164%), whereas nuclear MEK activity did not change, indicating that MEK-induced activation of MAPKs occurred in the cytosolic compartment. Activation of MAPKs after ischemic PC was completely blocked by the protein kinase C (PKC) inhibitor chelerythrine. Selective overexpression of PKC-ε in adult rabbit cardiomyocytes induced activation of both p44 and p42 MAPKs and reduced lactate dehydrogenase release during simulated ischemia-reperfusion, which was abolished by the MEK inhibitor PD-98059. The results demonstrate that 1) ischemic PC induces a rapid activation of p44 and p42 MAPKs in hearts of conscious rabbits; 2) the mechanism of this phenomenon involves activation of p44 and p42 MAPKs in the cytosol and their subsequent translocation to the nucleus; and 3) it occurs via a PKC-mediated signaling pathway. The in vitro data implicate PKC-ε as the specific isoform responsible for PKC-induced MAPK activation and suggest that p44/p42 MAPKs contribute to PKC-ε-mediated protection against simulated ischemia. The results are compatible with the hypothesis that p44 and p42 MAPKs may play a role in myocardial adaptations to ischemic stress.
L-type Ca2+current in guinea pig ventricular myocytes treated with modulators of tyrosine phosphorylation
Authors: Ogura Toshitsugu , Shuba Lesya M. , McDonald Terence F.
Published: December 2017

Guinea pig ventricular myocytes in whole cell configuration were treated with tyrosine kinase (TK) inhibitors [genistein (Gst), tyrphostin A23 (T23), and tyrphostin A25 (T25)] and with inactive analogs [daidzein, genistin, and tyrphostin A1 (T1)] to measure effects on L-type Ca2+current ( ICa,L). Gst inhibited ICa,L(IC50= 47 μM) without affecting its time course or shifting the ICa,L-voltage relationship. At the highest concentration of isoflavone tested (200 μM), ICa,Lwas inhibited by 66 ± 7% (Gst), 22 ± 2% (daidzein), and 1 ± 3% (genistin). Inhibition of ICa,Lby the active tyrphostins was significantly larger than inhibition by T1; at 200 μM the inhibitions were 72 ± 6% (T23), 71 ± 6% (T25), and 27 ± 6% (T1). The phosphotyrosine phosphatase inhibitor orthovanadate (1 mM) had a small stimulatory effect (6 ± 2%) on basal ICa,Land blocked the inhibition of ICa,Lby TK inhibitors. The data suggest a role for the TK-phosphotyrosine phosphatase system in the regulation of cardiac Ca2+channels.
Contamination of lymph from the major prenodal cardiac lymphatic in dogs
Authors: Geissler Hans J. , Davis Karen L. , Laine Glen A. , Brennan Michael L. , Mehlhorn Uwe , Allen Steven J.
Published: December 2017

Cannulation of the canine major prenodal cardiac lymphatic (MPCL) is the most common approach for the investigation of myocardial lymphatic function. However, the assumption that the MPCL drains pure cardiac lymph has been questioned. We studied variations of MPCL anatomy and investigated whether noncardiac lymph is drained by this lymphatic. After dye was injected into the lungs and left ventricular myocardium in 21 dogs, dissection of the cardiac lymphatic system yielded 3 anatomic variations. In variations 1 and 2 (81% of dogs), a mixture of cardiac and pulmonary lymph was drained via the MPCL. In variation 3 (19% of dogs) no connection was found between MPCL and pulmonary lymphatics. In variations 1 and 2, alteration of tidal volume resulted in significant changes of lymph flow rate. The pulmonary contribution to MPCL lymph flow was estimated as 34% in variation 2. We conclude that MPCL lymph may contain not only cardiac lymph but also significant pulmonary contamination. This finding should be considered in the interpretation of lymph data from cannulation of the canine MPCL.
Activation of visceral afferents by bradykinin and ischemia: independent roles of PKC and prostaglandins
Authors: Guo Zhi-Ling , Symons J. David , Longhurst John C.
Published: December 2017

We have shown that the cyclooxygenase (COX) and protein kinase C (PKC) systems both contribute to afferent activation in response to bradykinin (BK) and abdominal ischemia. Because the contribution from PKC to C fiber activation may depend, in part, on prostaglandin production, we hypothesized that an intact COX system is required for PKC-induced activation of ischemically sensitive abdominal visceral afferents by BK and abdominal ischemia. Single-unit activity of abdominal visceral C fibers was recorded from the right thoracic sympathetic chain of anesthetized cats. Three repeated injections of BK (1–2 μg/kg ia) produced similar increases in afferent activity from the baseline of 1.32 ± 0.24, 1.37 ± 0.32, and 1.41 ± 0.24 impulses/s ( n = 5). In another group of animals ( n = 5), the second and third BK injections were performed after COX inhibition (indomethacin; 5 mg/kg iv) and then combined COX + PKC inhibition [PKC-(19—36), 20 μg/kg iv], respectively. Inhibition of COX reduced ( P < 0.05) the afferent response to BK (0.59 ± 0.12 impulses/s) compared with the unblocked condition (1.14 ± 0.27 impulses/s), whereas combined COX + PKC inhibition further attenuated the increase from baseline (0.18 ± 0.09 impulses/s; P < 0.05). Similar results were obtained in a third group of cats when the antagonists were administered in reverse order ( n = 7). In a fourth group of cats ( n = 9) that were pretreated with indomethacin, ischemia increased afferent activity (0.78 ± 0.17 impulses/s). However, neural activity was attenuated (0.51 ± 0.14 impulses/s; P < 0.05) during a second bout of ischemia in the presence of indomethacin + PKC-(19—36). These results suggest that the contribution from PKC to the activation of ischemically sensitive C fibers, particularly by BK, does not require an intact cyclooxygenase system.
Mechanical activity in heart regulates translation of α-myosin heavy chain mRNA but not its localization
Authors: Nikcevic Gordana , Heidkamp Maria C. , Perhonen Merja , Russell Brenda
Published: December 2017

Mechanical inactivity depresses protein expression in cardiac muscle tissue and results in atrophy. We explore the mechanical transduction mechanism in spontaneously beating neonatal rat cardiomyocytes expressing the α-myosin heavy chain (α-MyHC) isoform by interfering with cross-bridge function [2,3-butanedione monoxime (BDM), 7.5 mM] without affecting cell calcium. The polysome content and α-MyHC mRNA levels in fractions from a sucrose gradient were analyzed. BDM treatment blocked translation at initiation (162 ± 12% in the nonpolysomal RNA fraction and 43 ± 6% in the polysomal fraction, relative to control as 100%; P < 0.05). There was an increase in α-MyHC mRNA from the nonpolysomal fraction (120.5 ± 7.7%; P < 0.05 compared with control) with no significant change in the heavy polysomes. In situ hybridization of α-MyHC mRNA was used to estimate message abundance as a function of the distance from the nucleus. The mRNA was dispersed through the cytoplasm in spontaneously beating cells as well as in BDM-treated cells (no significant difference). We conclude that direct inhibition of contractile machinery, but not calcium, regulates initiation of α-MyHC mRNA translation. However, calcium, not pure mechanical signals, appears to be important for message localization.
Systemic and microcirculatory effects of autologous whole blood resuscitation in severe hemorrhagic shock
Authors: Kerger Heinz , Waschke Klaus F. , Ackern Klaus V. , Tsai Amy G. , Intaglietta Marcos
Published: December 2017

Systemic and microcirculatory effects of autologous whole blood resuscitation after 4-h hemorrhagic shock with a mean arterial pressure (MAP) level of 40 mmHg were investigated in 63 conscious Syrian golden hamsters. Microcirculation of skeletal skin muscle and subcutaneous connective tissue was visualized in a dorsal skinfold. Shed blood was retransfused within 30 min after 4 h. Animals were grouped into survivors in good (SG) and poor condition (SP) and nonsurvivors (NS) according to 24-h outcome after resuscitation and studied before shock, during shock (60, 120, and 240 min), and 30 min and 24 h after resuscitation. Microvascular and interstitial[Formula: see text] values were determined by phosphorescence decay. Shock caused a significant increase of arterial[Formula: see text] and decrease of[Formula: see text], pH, and base excess. In the microcirculation, there was a significant decrease in blood flow (Q˙B), functional capillary density (FCD; capillaries with red blood cell flow), and interstitial [Formula: see text][1.8 ± 0.8 mmHg (SG), 1.3 ± 1.3 mmHg (SP), and 0.9 ± 1.1 mmHg (NS) vs. 23.0 ± 6.1 mmHg at control]. Blood resuscitation caused immediate MAP recompensation in all animals, whereas metabolic acidosis, hyperventilation, and a significant interstitial [Formula: see text] decrease (40–60% of control) persisted. In NS (44.4% of the animals), systemic and microcirculatory alterations were significantly more severe both in shock and after resuscitation than in survivors. Whereas in SG (31.8% of the animals) there was only a slight (15–30%) but still significant impairment of microscopic tissue perfusion (Q˙B, FCD) and oxygenation at 24 h, SP (23.8% of the animals) showed severe metabolic acidosis and substantial decreases (≥50%) of FCD and interstitial[Formula: see text]. FCD, interstitial[Formula: see text], and metabolic state were the main determinants of shock outcome.
Myogenic reactivity of rat epineurial arterioles: potential role in local vasoregulatory events
Authors: Wang Hong Xin , Davis Michael J. , Rajanayagam M. A. Sharmini , Potocnik Simon J. , Hill Michael A.
Published: December 2017

Local control of neural blood flow is considered to reside in innervation of epineurial and endoneurial arterioles rather than in intrinsic autoregulatory mechanisms. With the use of an isolated vessel preparation and an in vivo approach, the present studies examined intrinsic vasomotor responsiveness of epineurial arterioles. Segments of epineurial arterioles, cannulated on glass micropipettes (40 μm) and pressurized in the absence of intraluminal flow, showed sustained pressure-dependent (30–90 mmHg) vasoconstriction and acute myogenic reactivity. Myogenic tone was unaffected by phentolamine (10−6M). Removal of extracellular Ca2+resulted in loss of spontaneous tone and passive behavior. Concentration-response curves for norepinephrine (10−9–3 × 10−6M) and relaxation to both acetylcholine (10−8–10−5M) and adenosine (10−8–10−4M) were obtained. Acetylcholine dilator responses were inhibited by NG-nitro-l-arginine methyl ester. Epineurial blood flow was measured in vivo using a laser-Doppler flow probe. Blood flow declined over a 2-h period after surgery, and during this time preparations developed responsiveness to the dilator acetylcholine. Phentolamine blocked vasoconstrictor responses to exogenous norepinephrine but only partially reversed the in vivo baseline tone. The time-dependent decline in epineurial blood flow was observed despite the presence of tetrodotoxin (1 μM), further confirming that tone was predominantly caused by myogenic rather than neurogenic mechanisms. It is concluded that because epineurial arterioles exhibit intrinsic myogenic reactivity, they have the potential to participate in local regulation of neural hemodynamics independently of their own innervation.
Adenosine A3-receptor stimulation attenuates postischemic dysfunction through KATP channels
Authors: Thourani Vinod H. , Nakamura Masanori , Ronson Russell S. , Jordan James E. , Zhao Zhi-Qing , Levy Jerrold H. , Szlam Fania , Guyton Robert A. , Vinten-Johansen Jakob
Published: December 2017

We tested the hypothesis that selective adenosine A3-receptor stimulation reduces postischemic contractile dysfunction through activation of ATP-sensitive potassium (KATP) channels. Isolated, buffer-perfused rat hearts ( n = 8/group) were not drug pretreated (control) or were pretreated with adenosine (20 μM), 2-chloro- N 6-(3-iodobenzyl)-adenosine-5′- N-methyluronamide (Cl-IB-MECA; A3 agonist, 100 nM), Cl-IB-MECA + 8-(3-noradamantyl)-1,3-dipropylxanthine (KW-3902; A1 antagonist, 5 μM), Cl-IB-MECA + glibenclamide (Glib; KATP-channel blocker, 0.3 μM), or Glib alone for 12 min before 30 min of global normothermic ischemia followed by 2 h of reperfusion. After 2 h of reperfusion, left ventricular developed pressure (LVDP, %baseline) in control hearts was depressed to 34 ± 2%. In hearts pretreated with Cl-IB-MECA, there was a statistically significant increase in LVDP (50 ± 6%), which was reversed with coadministration of Glib (37 ± 1%). Control hearts also showed similar decreases in left ventricular peak positive rate of change in pressure (dP/d t). Therefore, the A3 agonist significantly attenuated postischemic cardiodynamic injury compared with the control, which was reversed by Glib. Cumulative creatine kinase (CK in U/min) activity was most pronounced in the control group (10.4 ± 0.6) and was significantly decreased by Cl-IB-MECA (7.5 ± 0.4), which was reversed by coadministration of Glib (9.4 ± 0.2). Coronary flow was increased during adenosine infusion (160% of baseline) but not during Cl-IB-MECA infusion. Effects of Cl-IB-MECA were not reversed by the specific A1 antagonist KW-3902. We conclude that cardioprotection afforded by A3-receptor stimulation may be mediated in part by KATP channels. Cl-IB-MECA may be an effective pretreatment agent that attenuates postischemic cardiodynamic dysfunction and CK release without the vasodilator liability of other adenosine agonists.
Transmural metabolic heterogeneity at high cardiac work states
Authors: Gong Guangrong , Uğurbil Kâmil , Zhang Jianyi
Published: December 2017

This study compared the transmural distribution of high-energy phosphate (HEP) depletion during oxidative stress induced by pacing- and dobutamine-induced tachycardia in myocardium perfused by a flow-limiting coronary stenosis. Myocardial blood flow (MBF) was measured with radioactive microspheres. Creatine phosphate (CrP), ATP, and Pi were measured with transmurally localized 31P NMR spectroscopy. In normal dogs a hydraulic occluder was used to produce a left anterior descending coronary artery stenosis, which maintained constant flow measured with a Doppler probe. Tachycardia was induced by rapid pacing (200 beats/min, n = 11) or by dobutamine infusion (20 μg ⋅ kg−1 ⋅ min−1 iv, n = 13) to produce a similar heart rate. In the presence of stenosis, pacing and dobutamine caused similar reductions of subendocardial (Endo)-to-subepicardial (Epi) MBF ratios (0.66 ± 0.06 vs. 0.63 ± 0.08, respectively). Stenosis plus pacing caused a decrease of the CrP-to-ATP ratio (CrP/ATP) in Endo from 2.00 ± 0.07 to 1.65 ± 0.08 ( P < 0.05) with no significant change in Epi. Stenosis plus dobutamine caused HEP changes across the left ventricular wall, which were most marked in the outer myocardial layer (Epi CrP/ATP decreased from 2.33 ± 0.11 to 1.67 ± 0.12; Endo CrP/ATP decreased from 1.99 ± 0.09 to 1.64 ± 0.12). Thus HEP changes during oxidative stress that are produced by pacing parallel the pattern of hypoperfusion and are most severe in the subendocardium. In contrast, in response to inotropic stimulation, the transmural metabolic changes did not correspond to the pattern of the hypoperfusion.
Ultrastructural assessment of myocardial necrosis occurring during ischemia and 3-h reperfusion in the dog
Authors: Becker Lewis C. , Jeremy Richmond W. , Schaper Jutta , Schaper Wolfgang
Published: December 2017

To determine whether myocardial necrosis may occur during postischemic reperfusion, electron microscopy was used to identify morphological features of irreversible injury in myocardial samples taken from anesthetized dogs with 90-min ischemia and 0-, 5-, 90-, or 180-min reperfusion. In samples without detectable collateral blood flow, necrosis was almost complete, whether or not the myocardium was reperfused. In samples with collateral flow, necrosis was more frequent after 180-min reperfusion than in the absence of reperfusion, despite similar collateral flows in the two groups. Excess of necrosis after 180-min reperfusion was evident in endocardium (ischemia only: 4 of 13, 180-min reflow: 14 of 20; P = 0.03) and midwall (ischemia only: 9 of 25, 180-min reflow: 29 of 45; P = 0.02). Multiple logistic regression with variables of collateral flow and transmural position was used to determine risk of irreversible injury in 111 samples from ischemic myocardium without reperfusion (model predictive accuracy = 75%, P < 0.00001) and to predict risk of necrosis in myocardium reperfused for 180 min. Of 65 samples from endocardium and midwall with detectable collateral flow, the model predicted necrosis in 23 samples but necrosis was observed in 43 samples ( P < 0.01). Reperfusion duration was a determinant of frequency of irreversible injury. Multiple logistic regression for 186 samples from myocardium reperfused for 5, 90, or 180 min showed that reperfusion duration was an independent predictor of irreversible injury ( P = 0.0003) when collateral flow and transmural location were accounted for. These findings are consistent with the occurrence of necrosis during reperfusion in myocardium exposed to substantial, prolonged ischemia but with sufficient residual perfusion to avoid necrosis during the period of flow impairment.
ANG II and baroreflex function in rabbits with CHF and lesions of the area postrema
Authors: Liu Jun-Li , Murakami Hiroshi , Sanderford Max , Bishop Vernon S. , Zucker Irving H.
Published: December 2017

Blockade of the angiotensin II (ANG II) type 1 receptor (AT1) has been shown to restore baroreflex sensitivity in rats and rabbits with experimental chronic heart failure (CHF). Because the modulation of baroreflex function in response to ANG II is mediated in part by AT1 receptors located in the area postrema, we hypothesized that lesions of the area postrema would prevent the enhancement in baroreflex function in response to AT1-receptor blockade in rabbits with pacing-induced CHF. Experiments were carried out on 24 male New Zealand White rabbits that were divided into sham ( n = 12) and lesioned ( n = 12) groups further divided into normal and CHF subgroups ( n = 6 each). All rabbits were identically instrumented to measure cardiac external dimensions, central venous pressure, arterial pressure, heart rate (HR), and renal sympathetic nerve activity (RSNA). After 3–4 wk of pacing, baroreflex sensitivity (infusions of phenylephrine and nitroprusside) was evaluated before and after intravenous administration of the AT1-receptor antagonist L-158,809. Maximum baroreflex sensitivity in nonpaced rabbits was 5.4 ± 0.7 beats ⋅ min−1 ⋅ mmHg−1and 5.2 ± 0.5% of maximum/mmHg for HR and RSNA curves, respectively, and was not altered by L-158,809 in either intact or lesioned rabbits. In contrast, L-158,809 enhanced baroreflex sensitivity in intact rabbits with CHF (HR from 1.6 ± 0.3 to 4.1 ± 0.7 beats ⋅ min−1 ⋅ mmHg−1, P < 0.001; RSNA from 2.3 ± 0.2 to 4.9 ± 0.4% of maximum/mmHg, P < 0.001). However, in CHF rabbits with area postrema lesions, L-158,809 failed to enhance baroreflex sensitivity. Interestingly, area postrema lesions did not normalize the baroreflex in CHF rabbits. From these data we conclude that the area postrema mediates the normalization of baroreflex sensitivity after AT1 blockade in rabbits with CHF but does not modify resting baroreflex function.
Enhanced ETA-receptor-mediated inhibition of Kvchannels in hypoxic hypertensive rat pulmonary artery myocytes
Authors: Li Kai-Xun , Fouty Brian , McMurtry Ivan F. , Rodman David M.
Published: December 2017

Endothelin (ET)-1 has been implicated as a critical mediator in the pathogenesis of hypoxic pulmonary hypertension. We questioned whether, during exposure to chronic hypobaric hypoxia, rat pulmonary artery smooth muscle cells (PASMC) became sensitized to ET-1. Two effects of ET-1, inhibition of voltage-gated K+(Kv) channels and release of intracellular Ca2+, were studied using whole cell patch clamp and single cell indo 1 fluorescence, respectively. In both normotensive and chronically hypoxic-hypertensive PASMC, ET-1 caused concentration-dependent inhibition of voltage-gated K+current [ IK(v)], with maximum inhibition of 12–18% seen at a concentration of 0.1–1 nM. Although the chronically hypoxic-hypertensive PASMC was no more susceptible to ET-1-mediated IK(v)inhibition, a switch in coupling between ET-1 and IK(v)from ETBto ETAreceptors occurred. This switch in receptor coupling, combined with reduced IK(v)density and increased ET-1 production in the hypoxic rat lung, may help explain the ability of ETA-receptor blockers to attenuate the development of hypoxic pulmonary hypertension in vivo.