bluuebunny/crossref_metadata_2025 huggingface dataset:
Losartan improves baroreflex control of heart rate of coarcted hypertensive rats
Authors: Santos C. M. , Pontieri V. , Leomil Neto M. , Michelini L. C.
Published: December 2017

To assess the role of angiotensin (ANG) II in both the increased heart rate (HR) and the impaired baroreceptor reflex control of HR that characterize the chronic phase of coarctation hypertension (CH), we compared basal HR, mean arterial pressure (MAP), and baroreflex sensitivity of coarcted hypertensive rats treated chronically with losartan, captopril, or vehicle. Baseline HR was recorded daily, and MAP and reflex HR changes and plasma renin activity (PRA) were measured in coarcted and sham-coarcted rats on the 5th day after coarctation. Both captopril (10 mg.kg-1.day-1 po) and losartan (10 mg.kg-1.day-1 po) caused a small nonsignificant reduction of hypertension (132 +/- 5 and 133 +/- 5, respectively, vs. 147 +/- 9 mmHg in vehicle-treated rats), but equally inhibited the late tachycardic phase (-37 +/- 13 and -29 +/- 12 beats/min in captopril- and losartan-treated groups, respectively, vs. +79 +/- 19 beats/min in vehicle treated rats). Similar results were obtained for other groups of coarcted hypertensive rats after suppression of PRA by bilateral nephrectomy. Although hypertensive levels were the same during both treatments, only losartan given orally or intracerebroventricularlly (1.25 micrograms.kg-1.h-1) was effective in improving the reflex bradycardia. The depressed reflex tachycardia was corrected by chronic oral treatment with losartan. The data suggest that the tachycardia occurring in the chronic phase of CH is mediated by blood-borne ANG II and that the normalization of the reflex control of HR by losartan is achieved by blockade of type I receptors of ANG II in central areas accessible to oral or centrally administered losartan but not to oral captopril.
Selective binding of platelet factor 4 to regions of active angiogenesis in vivo
Authors: Hansell P. , Maione T. E. , Borgstrom P.
Published: December 2017

In a previous study we suggested that recombinant human platelet factor 4 (rhPF4) preferentially binds in vivo to regions of active angiogenesis/endothelial cell migration. To test this hypothesis, binding of fluorescently labeled rhPF4 to newly formed vessels was compared with that of the normal skin vasculature, using syngeneic Langerhans islets as inducers of angiogenesis. Islets were implanted in the dorsal skinfold chamber of the hamster, and the binding of rhPF4 was studied using intravital fluorescence microscopy. Intra-arterially injected rhPF4 labeled, with high intensity, the endothelium along newly formed vessels of the islets (1,632 +/- 617 microns labeled vessel length per islet), and only on rare occasions (1 +/- 2 sites per cm2 skinfold) were short (62 +/- 48 microns) intense-labeled sites found in the normal vasculature of the skinfold. Heparin could displace most of the label if injected within 10 min after the rhPF4 injection, but not 30 min after. In conclusion, rhPF4-preferentially binds to regions of active angiogenesis in vivo. On binding, rhPF4 is internalized as judged from a decreasing heparin sensitivity with time after rhPF4 injection. The infrequent rhPF4-labeling sites in the normal skin vasculature most likely represent regions of newly formed cells/migration, i.e., normal endothelial turnover, supporting our previous findings demonstrating that the occurrence of such regions is rare in the normal microvasculature. Furthermore, despite the previously demonstrated short half-life in plasma, systemically injected rhPF4 will target regions of angiogenesis with high affinity, thereby facilitating the antiangiogenic effect of PF4.
Increase of cardiac work is associated with decrease of mitochondrial NADH
Authors: Ashruf J. F. , Coremans J. M. , Bruining H. A. , Ince C.
Published: December 2017

In this study we investigated the effect of work and substrate supply on mitochondrial NADH/NAD+ using epicardial autofluorescence in rat hearts perfused according to Langendorff. To avoid vasoconstrictor effects during high work output, nitroprusside-containing Tyrode solution was used. Photobleaching was avoided by using discontinuous ultraviolet excitation for NADH fluorescence measurements. To increase work, heartbeat rate was raised from 5 to 7 Hz, and concomitantly left ventricular pressure was raised stepwise from 0 to +/- 90 mmHg. During substrate-limited (5.5 mM glucose) perfusions, increase in O2 consumption (3.5 +/- 0.4 mumol.min-1.g-1, mean +/- SE, n = 6) caused by increase of heartbeat rate was associated with a significant decrease of NADH fluorescence (-31 +/- 2.5%, mean +/- SE, n = 6). During perfusions with 10 mM pyruvate increase of O2 consumption (3.6 +/- 0.7 mumol.min-1.g-1, mean +/- SE, n = 6) was associated with significant decrease of NADH fluorescence (-20 +/- 2.6%, mean +/- SE, n = 6). These results suggest that a rise in mitochondrial NADH/NAD+ is not the primary stimulus for increase in respiration and that changes of mitochondrial NADH/NAD+ are secondary to changes in O2 consumption.
Mechanisms of conduction time hysteresis in rabbit atrioventricular node
Authors: Billette J. , Zhao J. , Shrier A.
Published: December 2017

The functional origin of atrioventricular nodal hysteresis was studied in isolated rabbit heart preparations. This hysteresis is characterized by asymmetric changes in nodal conduction time (NCT) occurring for symmetric changes in cycle length. The respective contribution of the nodal properties of recovery, facilitation, and fatigue to the beat-to-beat changes in NCT observed during paired symmetric ramps of decreasing and increasing cycle length was determined with specifically design stimulation protocols. Nodal hysteresis was found to be entirely accounted for by variations in the contribution of nodal recovery and fatigue properties observed at corresponding cycle lengths. The study establishes how this contribution varies on a beat-to-beat basis as a result of cycle length history. This holds true for the numerous changes in hysteresis observed in response to changes in the sequence and slope of the ramps. Facilitation clearly affected NCT during these responses but did not contribute to the hysteresis. Moreover, the study demonstrates that there is no inherent change in the characteristics of nodal function with the direction of the ramp that could account for the hysteresis. Thus nodal hysteresis arises from nodal functional properties of recovery and fatigue but does not constitute a distinct independent intrinsic property of the node.
Determination of myoglobin saturation of frozen specimens using a reflecting cryospectrophotometer
Authors: Voter W. A. , Gayeski T. E.
Published: December 2017

This report describes a method and instrumentation for determining myoglobin (Mb) oxygen saturation in skeletal muscle. Canine gracilis is frozen in situ using a liquid N2-cooled copper block. Transverse section surfaces of frozen unstained muscle are observed at -110 degrees C using a microspectrophotometric system. The Mb saturation is determined using epi-illumination and a four-wavelength optical method. A special aperture permits illumination of a 20-microns-square area, and the radius of the catchment volume is estimated to be approximately 60 microns, with the strongest signal arising from the central region. The equibestic wavelengths used were 546.6, 570.5, and 584.1 nm. The method was validated using the nonlinear multicomponent analysis method of Lubbers. End-point (0 and 100% saturation) calibration was set using ischemic and adenosine-treated highly oxygenated muscles, respectively. The effects of hemoglobin (Hb) and metmyoglobin (metMb) signal contamination were evaluated experimentally and by computer-mixing simulations. Mb saturation determinations adjacent to large vessels are to be avoided. MetMb and capillary Hb do not interfere with the determination. The reproducibility of the method is estimated to be +/- 5%.
Response of cerebral blood vessels to an endogenous inhibitor of nitric oxide synthase
Authors: Faraci F. M. , Brian J. E. , Heistad D. D.
Published: December 2017

We examined effects of NG,NG-dimethyl-L-arginine (asymmetric dimethylarginine, ADMA), an endogenous inhibitor of nitric oxide (NO) synthase, on cerebral vascular responses using cranial windows in anesthetized rats and rabbits. Under control conditions in rats, topical application of 10 and 100 microM ADMA constricted the basilar artery by 9 +/- 2 and 19 +/- 1% (SE; P < 0.05, n = 8), respectively, from a baseline diameter of 213 +/- 19 microns. ADMA (10 and 100 microM) produced marked inhibition of vasodilation in response to acetylcholine without inhibiting vasodilatation in response to nitroprusside. ADMA (1-100 microM) inhibited activity of brain NO synthase (measured as the conversion of L-[14C]arginine to L-[14C]citrulline). In cerebrum and cerebellum, 50% inhibition of activity of NO synthase was produced by 2.3 +/- 0.4 and 1.8 +/- 0.1 microM ADMA, respectively. In rabbits, treatment with ADMA (300 microM) decreased baseline diameter of cerebral arterioles (control diameter = 93 +/- 10 microns) by 11 +/- 2% (P < 0.05, n = 10). In response to 1 microM acetylcholine, cerebral arterioles dilated by 36 +/- 6 and 13 +/- 4% (P < 0.05 vs. control) in the absence and presence of ADMA, respectively. Effects of ADMA were prevented by L-arginine. Thus ADMA inhibits activity of brain NO synthase and relaxation of cerebral blood vessels in response to acetylcholine. Because ADMA is produced in relatively high concentrations in brain, it may be an important endogenous modulator of cerebral vascular tone under resting conditions and in response to vasoactive stimuli.
Regional vascular reserve in canine atria and ventricles during rest and exercise
Authors: Bauman R. P. , Rembert J. C. , Greenfield J. C.
Published: December 2017

Vascular reserve, which defines the capacity for further vasodilation in a given physiological or pathological condition, has not been measured in the canine atria. This study defines, in normal dogs, the regional vascular reserve simultaneously measured in the atria (appendage, nonappendage regions) and in the ventricles during rest and two levels of exercise. Blood flow was determined using 11.4 +/- 0.1 microns radiolabeled microspheres. Vascular reserve (percent for each region) is the ratio of vascular conductance during each condition to maximum vascular conductance. Maximum vascular conductance was estimated by infusing adenosine intravenously. For a given physiological condition regional vascular conductance varied two- to threefold. The vascular reserve of each of the regions decreased progressively from rest to mild exercise to moderate exercise. Regional vascular reserve for both atria, the right ventricle, and the epicardial layer of the left ventricle was essentially uniform for a given condition: rest 93 +/- 0.4%, mild exercise 81 +/- 1.2%, and moderate exercise 69 +/- 1.5%. This similarity in vascular reserve implies that for a given physiological condition a common mechanism precisely regulates myocardial perfusion in these cardiac regions as a function of the total vasodilator capacity.
The stable VIP analogue, Ro 24-9981, potentiates bradykinin-induced increases in clearance of macromolecules
Authors: Gao X. P. , Rubinstein I.
Published: December 2017

The purpose of this study was to determine whether the stable cyclic peptide analogue of human vasoactive intestinal peptide, Ro 24-9981, modulates bradykinin-induced plasma exudation in the oral mucosa and if so, to determine the mechanisms that mediated these responses. Using intravital microscopy, we found that suffusion of Ro 24-9981 had no significant effects on leaky site formation and clearance of fluorescein-isothiocyanate-dextran (mol mass 70 kDa) in the hamster cheek pouch. However, Ro 24-9981 significantly potentiated bradykinin-induced increases in leaky site formation and clearance of fluorescein-isothiocyanate-dextran (P < 0.05). These effects were specific because Ro 24-9981 had no significant effects on adenosine and calcium ionophore A23187-induced increases in leaky site formation and clearance of fluorescein-isothiocyanate-dextran. Furthermore, they were not mediated by cyclooxygenase products of arachidonic acid metabolism because indomethacin was ineffective. NG-nitro-L-arginine methyl ester, a selective inhibitor of nitric oxide synthase, but not NG-nitro-D-arginine methyl ester, significantly attenuated the effects of both bradykinin and Ro 24-9981 with bradykinin (P < 0.05). These responses were restored by L-arginine but not D-arginine. Collectively, these data indicate that bradykinin-induced plasma exudation in the oral mucosa was potentiated by Ro 24-9981 in a specific receptor-mediated fashion. These responses were mediated, in part, by the L-arginine/nitric oxide biosynthetic pathway.
Effects of diabetes on isometric tension as a function of [Ca2+] and pH in rat skinned cardiac myocytes
Authors: Hofmann P. A. , Menon V. , Gannaway K. F.
Published: December 2017

In diabetes a primary myocardial defect occurs that is characterized by decreases in systolic pressure and cardiac output. The present study investigates whether diabetes causes a decreased maximum tension-generating ability, decreased Ca2+ sensitivity of myofilaments, or no change in cardiac myofilament contractile properties at pH 7.0 and 6.6. Hearts from Wistar rats were excised and mechanically disrupted 6-10 wk after injection of streptozotocin. The resulting myocyte-size preparations of skinned myocardium were used to determine the steady-state tension-negative, log molar Ca2+ concentration (pCa) relation. Maximum tension was unchanged, and the pCa of half-maximum tension generation was 0.14 pCa units lower than control for skinned myocytes from diabetic rats at pH 7.0. A significantly lower than normal maximum tension was observed at pH 6.6 for cardiac myocytes from diabetic rats. Increased expression of beta-myosin heavy chain (MHC) occurred in hearts from diabetic rats. Two troponin T (TnT) isoforms in myocardium of adult rats were identified by Western blots. The ratio of the two TnT isoforms were altered in diabetes. Changes in cardiac MHC and TnT expression may contribute to the observed decrease in Ca2+ sensitivity of myofilaments at pH 7.0 and decreased maximum tension-generating ability at pH 6.6 in diabetes.
PKC mediates LPS- and phorbol-induced cardiac cell nitric oxide synthase activity and hypocontractility
Authors: McKenna T. M. , Li S. , Tao S.
Published: December 2017

Lipopolysaccharide (LPS) treatment impairs cardiac myocyte contractility in a nitric oxide synthase (NOS)-dependent manner. The objective of this study was to assess whether protein kinase C (PKC) transduces the LPS signal into an enhanced NOS activity in rat cardiac myocytes. LPS (100 ng/ml) stimulated myocyte PKC activity, inducible NOS (iNOS) expression, and NOS activity in a time- and protein synthesis-dependent fashion. Directly activating PKC with beta-phorbol 12,13-dibutyrate (beta-PDB) also induced myocyte iNOS synthesis and NOS activity and reduced electrically stimulated contractility, while the inactive alpha-PDB was ineffectual. Contractility could be restored to beta-PDB-incubated cells by superfusion with the NOS inhibitor N omega-nitro-L-arginine methyl ester. PKC blockade with sphingosine, chelerythrine, or calphostin-C precluded LPS- and beta-PDB-induced increases in NOS activity and protected contractility. Depletion of PKC by 18 h of incubation with beta-PDB in the presence of chelerythrine also blocked acquisition of enhanced NOS activity and contractile dysfunction when the myocytes were subsequently exposed to LPS. These findings suggest that PKC is a significant intracellular mediator for the effects of LPS on cardiac cell NOS activity and contractile function.
Modulation of coronary flow by left ventricular volume in the presence and absence of vasomotor tone
Authors: Manor D. , Williams S. , Ator R. , Bryant K. , Scheel K. W.
Published: December 2017

This study was undertaken to determine the relationship between left ventricular (LV) volume and coronary flow in the presence and absence of coronary vasomotor tone in arrested dog hearts. We utilized an isolated, blood-perfused, potassium-arrested dog heart preparation with vascular vasomotor tone present (n = 5) or after maximal vasodilation with adenosine (n = 7). LV volume was controlled with a balloon while left and right coronary flows were recorded. Left and right coronary flows were plotted as a function of LV volume, and the degree of interdependency was quantitatively assessed by the slope of the linear regression and the correlation coefficient (r) between coronary flow and LV volume. With vasomotor tone present, both left (slope = 0.01 +/- 0.06 min-1) and right (slope = -0.01 +/- 0.01 min-1) coronary arterial flows were maintained relatively constant over a wide range of LV volumes. After maximal vasodilation, left coronary flow decreased linearly with LV volume loading (slope = -2.51 +/- 0.47 min-1, r2 = 0.96 +/- 0.02), whereas right coronary flow, similar to the response with tone present, did not change relative to control in most cases. We conclude that changes in coronary vasomotor tone may take place with LV volume loading to compensate for the mechanical vascular resistance changes secondary to myocardial stretch.
Electromechanical coupling and the conducted vasomotor response
Authors: Xia J. , Duling B. R.
Published: December 2017

Conducted vasomotor responses are viewed as one mechanism that functionally integrates the microvasculature. It is hypothesized that the conducted vasomotor response is the result of an electrical current and its passive electrotonic spread along the length of a microvessel. We tested this hypothesis in isolated, unpressurized arterioles from the hamster cheek pouch using conventional intracellular membrane potential recording techniques. The mean resting membrane potential (RMP) was -67 mV. KCl and phenylephrine (PE) pulse-stimulation applied through micropipettes could both induce transient depolarizations and vasoconstrictions at the site of stimulation (local) and at conducted (560 microns) sites. It was noted, however, that the conducted vasomotor response could not be induced until the conducted electrical response exceeded a threshold of -45 mV for a minimum amount of time. The relationship between the amplitude of constriction and the amplitude-time area of depolarization above -45 mV was the same for local and conducted KCl and for conducted PE but was significantly different from that for local PE. Nifedipine greatly reduced the local and conducted mechanical but not electrical responses. Our results indicate that the conducted vasomotor responses are the result of the generation and subsequent conduction of electrical signals along the vessel but that the corresponding mechanical response occurs only when the electrical response exceeds a threshold level.
Filling characteristics of left ventricle in newborn lambs
Authors: Velvis H. , Klopfenstein H. S.
Published: December 2017

An integral component of increased cardiac performance during the immediate newborn period is an increased rate of left ventricular (LV) filling. To determine the factors that facilitate increased LV filling in newborns, we compared filling characteristics in chronically instrumented awake newborn (7 +/- 2 days old) and older lambs (55 +/- 5 days old). The studies were performed 4 +/- 2 days after surgery, during which pressure transducers, dimension crystals, a flow transducer, and vascular occluders were placed. Newborn lambs had an increased cardiac index (247 +/- 40 vs. 127 +/- 48 ml.kg-1.min-1; P< 0.01) due to an increased heart rate (223 +/- 24 vs. 120 +/- 9 beats/min; P < 0.01) despite a similar stroke volume index (1.1 +/- 0.1 vs. 1.1 +/- 0.5 ml/kg; not significant). In newborn lambs, indexed mean LV filling rates were more than twofold higher (10.5 +/- 2.5 vs. 4.6 +/- 1.7 ml.kg-1.s-1; P <0.01), and a much greater percentage of filling occurred in the first 35 ms after mitral valve opening (52 +/- 7 vs. 23 +/- 8%; P < 0.01). In newborn lambs, early diastolic filling was facilitated by more rapid LV relaxation (tau: 17.2 +/- 2.2 vs. 23.3 +/- 1.2 ms; P < 0.01) and a higher left atrial (LA) pressure at the time of mitral valve opening (11.6 +/- 2.4 vs. 7.2 +/- 3.2 mmHg; P < 0.05). LV filling in newborn lambs also occurred at the expense of a higher mean LA pressure (8.4 +/- 2.4 vs. 5.1 +/- 2.6 mmHg; P < 0.05). These findings improve our understanding of LV diastolic function in newborns.
Restoring forces assessed with left atrial pressure clamps
Authors: Bell S. P. , Fabian J. , Higashiyama A. , Chen Z. , Tischler M. D. , Watkins M. W. , LeWinter M. M.
Published: December 2017

A negative pressure (P) in the fully relaxed left ventricle (LV) indicates the presence of restoring forces generated during contraction. To assess restoring forces in the intact LV under physiological filling conditions, a servomotor system was used in anesthetized open-chest dogs (n = 8) to produce nonfilling diastoles by left atrial pressure (LAP) clamping during systole such that LAP was less than left ventricular pressure (LVP) during the subsequent diastole. Steady-state LV end-diastolic pressure (EDP) was varied by volume infusion from 4.0 +/- 1.5 (+/-SD) to 12.8 +/- 2.1 mmHg. The corresponding fully relaxed LVPs increased from -2.1 +/- 1.9 to 1.1 +/- 3.2 mmHg, P < 0.001. LAP clamping increased the rate of LVP fall by 34 +/- 28% (P < 0.001) during 10 ms after the LVP dropped below the level of the LVP-LAP crossover of the preceding normal beat. During clamped beats, two-dimensional echo revealed substantial downward displacement of the mitral valve (MV) leaflets despite the reversed LA-LV gradient and absence of filling. Thus 1) restoring forces are present at low physiological EDP but absent at high physiological EDP; 2) filling retards the rate of fall of LVP; 3) even in the absence of filling, the process of LV relaxation facilitates MV opening.
Reperfusion injury on cardiac myocytes after simulated ischemia
Authors: Vanden Hoek T. L. , Shao Z. , Li C. , Zak R. , Schumacker P. T. , Becker L. B.
Published: December 2017

The extent of cardiac injury incurred during reperfusion as opposed to that occurring during ischemia is unclear. This study tested the hypothesis that simulated ischemia followed by simulated reperfusion causes significant "reperfusion injury" in isolated chick cardiomyocytes. Cells were exposed to hypoxia, hypercarbic acidosis, hyperkalemia, and substrate deprivation for 1 h followed by 3 h of reperfusion. Irreversible cell membrane injury, measured by propidium iodide uptake, increased from 4% of cells at the end of ischemia to 73% after reperfusion; death occurred in only 17% of cells kept ischemic for 4 h. Lactate dehydrogenase release was consistent with these changes. Lengthening ischemia from 30 to 90 min increased cell injury as expected, but of the total cell death, > 90% occurred during reperfusion. "Chemical hypoxia" composed of cyanide (2.5 mM) plus 2-deoxyglucose augmented injury before reperfusion compared with simulated ischemia. Inhibition of oxygen radical generation by use of metal chelator 1,10-phenanthroline reduced cell death from 73% to 40% after reperfusion (P = 0.001). We conclude that simulated reperfusion significantly augments the cellular membrane damage elicited by simulated ischemia in isolated cardiomyocytes devoid of other factors and suggest that reactive oxygen species, perhaps from the mitochondria, participate in this injury.
A KATP channel opener protects cardiomyocytes from Ca2+ waves: a laser confocal microscopy study
Authors: Lopez J. R. , Ghanbari R. A. , Terzic A.
Published: December 2017

Laser confocal microscopy was used to visualize intracellular spatiotemporal Ca2+ patterns in single guinea pig ventricular myocytes loaded with the Ca2+ indicator, fluo 3-acetoxymethyl ester (fluo 3-AM), and exposed to moderately elevated extracellular K+ to induce partial membrane depolarization. Analysis of K(+)-induced intracellular Ca2+ elevation revealed three distinct paradigms: 1) diffuse, nonoscillatory Ca2+ elevation across the myocyte; 2) localized Ca2+ elevation in anatomically restricted areas (Ca2+ sparks); and 3) regenerative frontal propagations of Ca2+ that traversed the length of the cell (Ca2+ waves). The first two patterns were more frequently observed when the extracellular K+ concentration was raised to 8 mM. Ca2+ waves became more common when extracellular K+ concentration was increased to 16 mM, suggesting that a minimum threshold of increase in intracellular Ca2+ is necessary for the organization of Ca2+ waves. The velocity of propagation was typically approximately 60 microns/s with an average frequency of one wave per second crossing at a given point in the cell. Wave propagation resulted in spatial and temporal oscillations in cytosolic and nuclear Ca2+ concentration. Treating cardiac cells with aprikalim, a potassium channel-opening drug, prevented 16 mM K+ (but not 32 mM K+) from inducing an increase in Ca2+ concentration and from generating Ca2+ waves. In cardiomyocytes treated with glyburide, a selective antagonist of ATP-sensitive K+ channels, aprikalim failed to prevent 16 mM K+ from inducing Ca2+ waves. In summary, moderate hyperkalemia induces distinct nonuniform form patterns of intracellular Ca2+ elevation in ventricular cells, which can be prevented by a potassium channel-opening drug through a glyburide-sensitive mechanism.
Length-dependent activation in intact ferret hearts: study of steady-state Ca(2+)-stress-strain interrelations
Authors: Stennett R. , Ogino K. , Morgan J. P. , Burkhoff D.
Published: December 2017

We examined the steady-state stress-strain relationships and the steady-state stress-intracellular calcium concentration ([Ca2+]i) relationship in intact ferret hearts and compared these to previously published analogous relationships in skinned and intact muscle. Langendorff-perfused ferret hearts were treated with ryanodine and tetanized by rapid stimulation to create steady-state conditions. [Ca2+]i was measured concurrently by macroinjected aequorin. Over a range of volumes corresponding to strains between 1.0 and 0.75, steady-state stress decreased by 33% when saturating levels of perfusate calcium were used, indicating the degree to which physical factors contribute to the Frank-Starling relationship. The steady-state stress-[Ca2+]i relationship was sigmoidal with a mean Hill coefficient (nH) of 4.91 +/- 0.29 at a strain of 1.0, and the [Ca2+]i required for half-maximal activation (K1/2) was 0.41 +/- 0.03 microM. K1/2 increased and nH decreased with decreasing strains. These results are similar to those observed in intact muscle but differ quantitatively from results obtained in isolated, skinned preparations. Based on these results, we suggest that whole heart function can be related to average sarcomere function without the need for complex models of ventricular structure.
Local 24-h hyperglycemia does not affect endothelium-dependent or -independent vasoreactivity in humans
Authors: Houben A. J. , Schaper N. C. , de Haan C. H. , Huvers F. C. , Slaaf D. W. , de Leeuw P. W. , Nieuwenhuijzen Kruseman C.
Published: December 2017

Hyperglycemia induces regional hemodynamic changes, as suggested by animal studies. These hemodynamic changes may play an initiating role in the pathogenesis of diabetic microangiopathy. The aim of the present study was to evaluate the effects of acute local hyperglycemia for 24 h on basal human forearm muscle and skin blood flow and endothelium-dependent and -independent vasoreactivity. Local hyperglycemia (approximately 15 mM) was induced by infusion of 5% glucose into the brachial artery of the nondominant arm. In control experiments, the same individual amount of glucose was infused intravenously in the dominant arm to correct for possible systemic effects of the infused glucose. Vasoreactivity of the forearm vasculature was evaluated by local infusion of acetylcholine (ACh), sodium nitroprusside (SNP), NG-monomethyl-L-arginine (L-NMMA), and norepinephrine (NE) into the brachial artery. Regional hemodynamic measurements were performed at baseline and after 6, 12, and 24 h of local hyperglycemia. Median (with interquartile range) basal forearm (muscle) blood flow (FBF) was not influenced by the 24-h local hyperglycemia [infused-to-contralateral arm FBF ratio for glucose 1.32 (1.16–1.64) vs. control 1.54 (1.34–1.69)]. Skin microcirculatory blood flow (laser Doppler flowmetry, LDF) was not influenced by the 24-h local hyperglycemia [LDF ratio for glucose 1.00 (0.62–1.56) vs control 0.80 (0.58–1.14)]. In addition, the vasoreactivity of both muscle and skin (not shown) vasculature to ACh [percent change in FBF ratio for glucose 167% (81–263) vs. control 148% (94–211)], SNP [for glucose 486% (178–586) vs. control 293% (196–454)], L-NMMA [for glucose -36% (-56 to -22) vs. control -41% (-51 to -24)], and NE [for glucose -48% (-72 to -41) vs. control -66% (-79 to -33)] was also not affected by the local hyperglycemia. Thus, in contrast to animal studies, our results suggest that a moderate-to-severe hyperglycemia does not affect the regulation of basal blood flow or endothelium-dependent or -independent vasoreactivity in humans.
Sympathovagal interplay in the control of overall blood pressure variability in unanesthetized rats
Authors: Ferrari A. U. , Franzelli C. , Daffonchio A. , Perlini S. , Dirienzo M.
Published: December 2017

The role of sympathetic and parasympathetic influences in the control of overall blood pressure variability was studied in chronically instrumented, freely behaving Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) subjected to sympathectomy by 6-hydroxydopamine (100 micrograms/kg ip) twice in 1 wk (effectiveness verified by abolition of pressor and tachycardic response to tyramine, 150 mg/kg i.v.) and/or to cholinergic blockade by atropine (0.7 mg/kg i.v.). Overall heart rate and blood pressure variabilities were measured as variation coefficients computed beat to beat on 90-min blood pressure recordings. As compared with the vehicle-treated controls, sympathectomized rats had much larger blood pressure variability (WKY, +61%, SHR, +86%, both P < 0.01). Cholinergic blockade superimposed to sympathectomy caused heart rate variability to markedly fall and the already augmented blood pressure variability to further rise 47% in WKY and 28% in SHR (both P < 0.01). Prolonged observation of the animals revealed the systematic occurrence of rapid blood pressure falls occurring at the onset of locomotor activity, accounting for a substantial fraction of the sympathectomy-related increase in blood pressure variability. It is concluded that 1) under undisturbed daily life conditions, sympathetic influences oppose blood pressure variations, presumably by adjusting their vasoconstrictor influences to compensate for the metabolic vasodilation occurring in functionally active tissues; 2) when sympathetic vascular control is lost, vagally mediated heart rate variations oppose the rise in blood pressure variability, possibly via rapid changes in cardiac output that partly offset the fluctuations in total peripheral resistance; and 3) chronic hypertension fails to alter these cardiovascular regulatory mechanisms.
Noninvasive indexes of cardiac systolic and diastolic function in hyperthyroid and senescent mouse
Authors: Taffet G. E. , Hartley C. J. , Wen X. , Pham T. , Michael L. H. , Entman M. L.
Published: December 2017

The mouse is a common model for transgenic manipulation, however, their small size has made hemodynamic study difficult. A noninvasive 10-MHz pulsed Doppler probe was used to measure aortic and mitral flow velocities in anesthetized, intact mice to study the effects of aging and hypethyroidism (induced by thyroxine) one systolic and diastolic cardiac function. In 10 hyperthyroid mice peak aortic velocity (PAV, an index of systolic function) was 34% higher than in 10 control mice (108 +/- 2 vs. 80 +/- 3 cm/s, P < 0.05). The ratio of early to late mitral filling velocity (E/A ratio, an index of diastolic function) was 47% higher (5.6 +/- 0.8 vs. 3.8 +/- 0.2, P < 0.05) in the hyperthyroid mice. In six old (30 mo) mice PAV was similar to eight young (4 mo) mice (73 +/- 3 vs. 75 +/- 3 cm/s), but the E/A ratio was 59% lower (1.8 +/- 0.3 vs. 4.4 +/- 0.4, P < 0.05). Despite a wide range of observed heart rates, the systolic and diastolic parameters of the groups were clearly separated. We conclude that cardiac systolic and diastolic function in mice, measured by pulsed Doppler ultrasound, are similar to larger species both in magnitude and in their response to hyperthyroidism and aging.
Regional and functional factors determining induction and maintenance of atrial fibrillation in dogs
Authors: Wang J. , Liu L. , Feng J. , Nattel S.
Published: December 2017

The present study was designed to determine the factors governing the ability of premature beats at various atrial sites to initiate atrial fibrillation (AF) and the determinants of the duration of AF in dogs at 1-10 Hz. The site of atrial extrasystoles determined their ability to induce AF. Regional differences in AF inducibility were due to differences in local refractoriness. Premature beats initiated AF by blocking in regions of greater refractoriness, causing macroreentrant activation with subsequent disorganization producing fibrillation. The atrial refractory period and wavelength during rapid 1:1 atrial pacing were weak predictors of AF duration (r = 0.24 and 0.23, respectively), which depended strongly on variability in regional refractoriness measured by the standard deviation in local refractory periods (r = 0.80, P < 0.001) and on the heterogeneity of activation during AF (r = 0.74, P < 0.001). Thus, premature beats cause AF by initiating a single macroreentrant cycle that degenerates into multiple wavefronts, regional refractoriness is the primary determinant of AF induction by premature beats, and variability in refractoriness may be an important determinant of the ability of AF to sustain itself.
Proarrhythmic and antiarrhythmic actions of ion channel blockers on arrhythmias in the heart: model study
Authors: Chay T. R.
Published: December 2017

We explain why 1) some class I and IV antiarrhythmia drugs could exert proarrhythmic action, 2) some class III drugs are effective in controlling reentrant arrhythmias, and 3) cycle length (CL) oscillation is involved in the termination or initiation of reentry. To explain these phenomena, we employ the following three means: bifurcation analysis, simulation, and model construction. Antiarrhythmia drugs are modeled by varying maximal conductances of Na+, Ca2+, and time-dependent delayed rectifying and time-independent inward rectifying K+ channels in the Beeler-Reuter model, where the model cells are arranged in a ring. Bifurcation analysis predicts that there is a critical ring size (CRS) at which infinite ring behavior suddenly breaks down. Channel blockers can affect CRS in different manners: Na+ and Ca2+ blockers shorten CRS, whereas delayed rectifying K+ channel blockers and the inward K+ channel blockers lengthen CRS. This differential explains why some antiarrhythmia drugs are proarrhythmic (i.e., shorten CRS) whereas others are antiarrhythmic (i.e., lengthen CRS). Simulation is then used to investigate how the drugs affect reentrant rhythms in the neighborhood of the CRS. We find that, in this region, CL, conduction velocity, and action potential duration become oscillatory. As ring size shrinks, the pattern of the oscillation becomes more complex. When the ring shrinks to a certain size, reentry can no longer be sustained, and it terminates after a few oscillatory cycles. To explain the basic mechanism involved in CL oscillation, we then construct a minimal model that contains a low-threshold fast inward current and a high-threshold slow inward current. With this model, we show that the two inward currents, with vastly different activation and inactivation kinetics, cause CL oscillations. Our results thus give theoretical explanations for the experimental finding of Frame's group in canine atrial tricuspid ring in vitro that class IC drugs can bring about stable reentry from nonsustained transient reentry, whereas class III drugs transform stable reentry to complex oscillations in CL. Our results also support the result of Frame's group, in that, in "adjustable" tricuspid rings, CL oscillation becomes more complex and its period becomes shorter as an excitable gap is shortened.
Angiotensin II formation in dog heart is mediated by different pathways in vivo and in vitro
Authors: Balcells E. , Meng Q. C. , Hageman G. R. , Palmer R. W. , Durand J. N. , Dell'Italia L. J.
Published: December 2017

Angiotensin-converting enzyme (ACE) inhibitors (I) have beneficial effects that are presumably mediated by decreased angiotensin II (ANG II) production. However, in vitro assays in human heart extracts have demonstrated that > 75% of ANG II-forming enzyme activity was not inhibited by captopril (Cap) and therefore did not appear to be related to ACE but was inhibited by chymostatin, suggesting that it was predominantly chymase-like activity. Previous work in our laboratory has demonstrated a similar relative contribution of ACE and chymase-like activity toward ANG II formation in vitro in dog heart tissue extracts. Accordingly, we compared Cap-inhibitable ANG II formation in vitro in heart tissue of five adult mongrel dogs to the in vivo Cap-inhibitable, ANG II-forming activity across the myocardial bed in four openchest, adult mongrel dogs. In vitro studies demonstrated that only 6 +/- 2% of ANG II formation was inhibited by Cap from heart tissue extracts of the left ventricular midwall. In in vivo studies, ANG I (0.5 nmol/min) followed by ANG I plus the ACE inhibitor Cap (0.1 mumol/min) was infused into the left anterior descending artery, and ANG II was assayed in the proximal aorta and coronary sinus. The arterial-venous (A-V) difference of ANG II across the myocardial circulation increased significantly during ANG I infusion (-13.4 +/- 23.5 to 142.8 +/- 71.4 pg/ml; P < 0.03). Subsequent coinfusion of Cap with ANG I significantly decreased the myocardial A-V difference of ANG II by 60 +/- 18% (P < 0.05). Thus, in contrast to the in vitro situation, ANG II formation in vivo is inhibited significantly by Cap in the normal dog heart. This comparison of in vivo and in vitro conversion of ANG I to ANG II by ACE and chymase-like activity suggests that in vitro assays may underestimate the functional contribution of ACE to intracardiac ANG II formation.
Angiotensin II type 1 receptor-mediated activation of Ras in cultured rat vascular smooth muscle cells
Authors: Okuda M. , Kawahara Y. , Yokoyama M.
Published: December 2017

Angiotensin II (ANG II), a potent growth-promoting factor of vascular smooth muscle cells (VSMC), induces activation of mitogen-activated protein (MAP) kinases and subsequent expression of the c-fos protooncogene in VSMC. However, it remains obscure whether ANG II induces activation of the ras protooncogene product (Ras), and if it does, whether Ras is involved in signaling from the ANG II receptor to the MAP kinase pathway in VSMC. In cultured VSMC, ANG II activated Ras comparably to epidermal growth factor. ANG II-induced Ras activation was detectable within 1 min and maximal at 2–5 min. The ANG II type 1 (AT1) receptor antagonist, CV-11974, completely inhibited this reaction. Pertussis toxin treatment of VSMC inhibited ANG II-induced Ras activation by approximately 70% but had no effect on ANG II-induced MAP kinase activation and c-fos expression. These results indicate that ANG II activates Ras via AT1 receptors, which are predominantly linked to a G protein of the Gi subfamily in VSMC1 and suggest that Ras activation may not be a prerequisite for ANG II-induced MAP kinase activation and c-fos expression in this cell type.
Hydrogen peroxide induces leukocyte rolling: modulation by endogenous antioxidant mechanisms including NO
Authors: Johnston B. , Kanwar S. , Kubes P.
Published: December 2017

In this study, intravital microscopy was used to examine the mechanisms that regulate H2O2-induced leukocyte rolling within rat mesenteric venules in vivo. H2O2 elicited leukocyte rolling within a narrow response window between 10 and 500 microM H2O2. Continuous superfusion with 100 microM H2O2 induced a large but transient increase in the flux of rolling leukocytes, whereas a short 5-min pulse elicited a sustained increase in rolling flux. Both treatments caused increases in leukocyte adhesion. H2O2-induced increases in leukocyte flux and adhesion could be prevented with an anti-P-selectin antibody. Inhibition of endogenous catalase (aminotriazole), glutathione (diethyl maleate), or nitric oxide (NG-nitro-L-arginine methyl ester) shifted the effective concentration of H2O2; continuous superfusion with 10 microM H2O2 now elicited large and sustained increases in leukocyte rolling flux, whereas 100 microM H2O2 elicited less than optimal responses. Dual antioxidant inhibition further reduced the effective H2O2 concentration to 1 microM H2O2. A nitric oxide donor prevented the increased rolling flux induced by 100 microM H2O2. These findings suggest that endogenous antioxidants are important regulators of H2O2-induced, P-selectin-dependent leukocyte rolling in vivo.
Modulation of endothelium-derived nitric oxide in canine femoral veins
Authors: Miller V. M. , Barber D. A.
Published: December 2017

Experiments were designed to determine whether nitric oxide was the mediator of increased endothelium-dependent relaxations in veins proximal to an arteriovenous fistula. A fistula was prepared between femoral arteries and veins in dogs. After 6 wk, veins proximal to the fistula were removed, cut into rings, and suspended for the measurement of isometric force in organ chambers. In some rings the endothelium was removed deliberately. NG-monomethyl-L-arginine (L-NMMA) caused contraction in three of six fistula-operated veins with and without endothelium. In rings contracted submaximally with prostaglandin F2 alpha, acetylcholine and the alpha 2-adrenergic agonist UK-14,304 cause e tylcholine and the alpha 2-adrenergic agonist UK-14,304 caused endothelium-dependent, concentration-dependent relaxations that were greater in fistula compared with sham-operated veins. These relaxations were reduced by L-NMMA. Calcium ionophore A23187 caused comparable endothelium-dependent relaxations in fistula- and sham-operated veins that were unaffected by L-NMMA. There were no differences in either calcium-dependent or -independent activity of nitric oxide synthase isolated from fistula- and sham-operated veins. Positive staining for nitric oxide synthase was present in both the endothelium and media of fistula-operated veins. These results indicate that nitric oxide mediates increased endothelium-dependent relaxations to acetylcholine and alpha 2-adrenergic agonists in fistula-operated veins. Therefore, chronic increases in blood flow and oxygen tension modify selectively receptor-coupled production of nitric oxide in endothelium and smooth muscle of veins.
Central V1 AVP receptors are involved in cardiovascular adaptation to hypovolemia in WKY but not in SHR
Authors: Budzikowski A. S. , Paczwa P. , Szczepanska-Sadowska E.
Published: December 2017

The present study was designed to determine the role of centrally released arginine vasopressin (AVP) in cardiovascular adaptation to hypotensive hypovolemia in conscious normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Three groups of experiments were performed on WKY and SHR chronically implanted with lateral cerebral ventricle (LCV) cannulas and with femoral artery catheters. Mean arterial pressure (MAP) and heart rate (HR) were monitored before and after arterial bleeding (1.3% body weight) performed during LCV infusion 1) artificial cerebrospinal fluid (control), 2) V1 AVP-receptor antagonists inverted question mark[d(Et2)Tyr(Me)]DAVP, 5 ng/min inverted question mark, and 3) V2 AVP-receptor antagonists inverted question mark[d(CH2)5-D-Ile2, Ile4, AlaNH2]AVP, 5 ng/min inverted question mark. In control experiments hemorrhage caused similar significant decreases of MAP in both strains and bradycardia in WKY. Blockade of central V1 AVP receptors abolished hemorrhagic bradycardia and significantly reduced hypotension in WKY, with no effect on HR and MAP responses to hypovolemia in SHR. Neither in WKY nor in SHR were the cardiovascular responses to hemorrhage altered by blockade of central V2 receptors. The results suggest that the central V1 AVP system plays a significant role in eliciting hypovolemic bradycardia and hypotension in WKY and that this function is significantly impaired in SHR.
Repeated cocaine administration reduces bradykinin-induced dilation of pial arterioles
Authors: Copeland J. R. , Willoughby K. A. , Police R. J. , Ellis E. F.
Published: December 2017

Using the acute cranial window technique in rabbits under surgical anesthesia, we tested the vasoactivity of acetylcholine (ACh, 10(-8)-10(-5) M), bradykinin (BK, 10(-8)-10(-5) M), and asphyxia (10% O2, 9% CO2, balance N2) after subchronic pretreatment with cocaine. After repeated administration of cocaine (20 mg.kg-1.day-1 sc x 7 days), the BK-induced dilation of pial arterioles was reduced by 51%. Previous work showed that BK produces dilation of pial arterioles by a cyclooxygenase-dependent oxygen radical-mediated mechanism and that in rabbits the BK-induced dilation is dependent on both vascular and nonvascular cyclooxygenase. Selective blockade of vascular cyclooxygenase, in addition to cocaine treatment, did not produce any greater inhibition of the BK-induced dilation. The dilation in response to ACh and asphyxia was unaltered by cocaine. Levels of cerebrospinal fluid prostaglandins suggest cocaine pretreatment may inhibit cerebral vascular prostaglandin production. Together, cerebrospinal fluid prostaglandin and vasoreactivity data indicate cocaine pretreatment selectively inhibits the vascular cyclooxygenase-dependent mechanism mediating the BK-induced dilation. This decreased response to BK in cocaine-treated rabbits may result from decreased oxygen radical production concomitant with decreased vascular prostaglandin production. Alternatively, oxygen radical scavenging may be increased after cocaine treatment. We speculate that cocaine-induced alterations in cerebrovascular function and metabolism may be related to the increased incidence of stroke reported to occur in human cocaine users.