bluuebunny/crossref_metadata_2025 huggingface dataset:
Is hydrogen peroxide an EDHF in human radial arteries?
Authors: Hamilton C. A. , McPhaden A. R. , Berg G. , Pathi V. , Dominiczak A. F.
Published: December 2017

In human radial arteries, a nitric oxide/prostanoid-independent mechanism that has the pharmacological characteristics of an EDHF contributes to endothelium-dependent relaxation. H2O2 can act as an EDHF in some vascular beds. We examined the hypothesis that endogenously produced H2O2 mediated the nitric oxide/prostanoid-independent relaxation to carbachol in radial arteries obtained from patients undergoing coronary artery bypass surgery. Superoxide levels, measured by chemiluminescence, were similar in radial and internal mammary arteries, but immunohistochemical staining for Cu/Zn superoxide dismutase (SOD) was lower in endothelium from radial arteries. In organ chamber studies, neither addition of catalase nor addition of SOD to the bathing fluid modified nitric oxide/prostanoid-independent relaxations to carbachol in radial arteries. However, nitric oxide-dependent vasorelaxation was enhanced in the presence of SOD. Thus the nitric oxide/prostanoid-independent relaxation to carbachol is not due to H2O2 and, unlike nitric oxide-mediated vasorelaxation, is not attenuated by superoxide. Blood vessels showing EDHF-mediated relaxations resistant to oxidative stress may provide favorable outcomes in revascularization surgery.
Gender-specific compensation for the lack of NO in the mediation of flow-induced arteriolar dilation
Authors: Wu Yuming , Huang An , Sun Dong , Falck John R. , Koller Akos , Kaley Gabor
Published: December 2017

Flow-induced dilation of gracilis muscle arterioles was examined in both genders of control rats and rats chronically treated with N ω-nitro-l-arginine methyl ester (l-NAME). After l-NAME treatment (4 wk), systolic blood pressure was significantly increased compared with control, whereas the plasma concentration of nitrate/nitrite was significantly reduced. Isolated and pressurized arterioles dilated significantly in response to increases in flow (0–25 μl/min). Flow-induced dilation was comparable in arterioles of control andl-NAME-treated rats but was significantly greater in female than in male rats. l-NAME + indomethacin, which abolished flow-induced dilation in arterioles of male control rats, inhibited the dilation by only ∼75% in female control rats. The residual portion of the response was eliminated by additional administration of miconazole, an inhibitor of cytochrome P-450. Indomethacin did not affect the dilation in femalel-NAME-treated rats but completely inhibited the response in male l-NAME-treated rats. The indomethacin-insensitive, flow-induced dilation in female l-NAME-treated arterioles was abolished by miconazole, 6-(2-proparglyoxyphenyl)hexanoic acid, or charybdotoxin. Thus an augmented release of endothelial prostaglandins accounts for the preserved flow-induced dilation in arterioles of male rats, whereas a metabolite of cytochrome P-450 is responsible for the maintenance of flow-induced dilation in female rats, suggesting important differences in the adaptation of the endothelium of arterioles from male and female rats to the lack of nitric oxide (NO) synthesis.
Shear stress-induced vasodilation in porcine coronary conduit arteries is independent of nitric oxide release
Authors: Dube Sandeep , Canty John M.
Published: December 2017

The present study was performed to determine the importance of nitric oxide in eliciting epicardial coronary artery dilation during sustained increases in shear stress in the absence of pulsatile flow. Isolated first-order porcine epicardial coronary conduit arteries (∼500 μm) were preconstricted (U-46619) and subjected to steady-state changes in flow in vitro. Nonpulsatile flow (shear stress range from 0 to ∼100 dyn/cm2) produced a graded dilation of epicardial arteries. Inhibiting nitric oxide synthase with 10−5 M N ω-nitro-l-arginine methyl ester (l-NAME) blocked bradykinin-induced vasodilation but did not affect the flow-diameter relation or the maximum change in diameter from static conditions (67 ± 10 μm in control vs. 71 ± 8 μm after l-NAME, P = not significant). The addition of indomethacin (10−5 M) had no effect on flow-mediated vasodilation. Depolarizing vascular smooth muscle with KCl (60 mM) or removing the endothelium blocked bradykinin vasodilation and completely abolished flow-mediated responses. The K+channel blocker tetraethylammonium chloride (TEA; 10−4M) attenuated flow-mediated vasodilation (maximum diameter change was 110 ± 18 μm under control conditions vs. 58 ± 10 μm after TEA, P < 0.001). These data indicate that epicardial coronary arteries dilate to steady-state changes in nonpulsatile flow via a mechanism that is independent of nitric oxide production. The ability to completely block this with KCl and attenuate it with TEA supports the hypothesis that epicardial coronary arteries dilate to steady levels of shear stress through hyperpolarization of vascular smooth muscle. This may be secondary to the release of an endothelium-dependent hyperpolarizing factor.
Nitric oxide inhibition abolishes sleep-wake differences in cerebral circulation
Authors: Zoccoli G. , Grant D. A. , Wild J. , Walker A. M.
Published: December 2017

Nitric oxide (NO), being produced by active neurones and also being a cerebral vasodilator, may couple brain activity and blood flow in sleep, particularly during active sleep (AS), which is characterized by widespread neural activation and markedly elevated cerebral blood flow (CBF) compared with quiet wakefulness (QW) and quiet sleep (QS). This study examined CBF and cerebral vascular resistance (CVR) in lambs ( n = 6) during spontaneous sleep-wake cycles before and after infusion of N ω-nitro-l-arginine (l-NNA), an inhibitor of NO synthase. l-NNA infusion produced increases in CVR and decreases in CBF during all sleep-wake stages, with the greatest changes occurring in AS (ΔCVR, 88 ± 19%; ΔCBF −24 ± 8%). The characteristic CVR and CBF differences among AS, QS, and QW disappeared within 1–3 h ofl-NNA infusion, but had reappeared by 24 h despite persisting cerebral vasoconstriction. These experiments show that NO promotes cerebral vasodilatation during sleep as well as wakefulness, particularly during AS. Additionally, NO is the major, although not sole, determinant of the CBF differences that exist between sleep-wake states.
ATP-mediated release of arachidonic acid metabolites from venular endothelium causes arteriolar dilation
Authors: Hammer Leah W. , Ligon Alison L. , Hester Robert L.
Published: December 2017

This study was designed to test the hypothesis that venular administration of ATP resulted in endothelium-dependent dilation of adjacent arterioles through a mechanism involving cyclooxygenase products. Forty-three male golden hamsters were anesthetized with pentobarbital sodium (60 mg/kg ip), and the cremaster muscle was prepared for in vivo microscopy. ATP (100 μM) injected into venules dilated adjacent arterioles from a mean diameter of 51 ± 4 to 76 ± 6 μm ( P < 0.05, n = 6). To remove the source of endothelial-derived relaxing factors, the venules were then perfused with air bubbles to disrupt the endothelium. Resting arteriolar diameter was not altered after disruption of the venular endothelium (51 ± 5 μm), and the responses to venular ATP infusions were significantly attenuated (59 ± 4 μm, P < 0.05). To determine whether the relaxing factor was a cyclooxygenase product, ATP infusion studies were repeated in the absence and presence of indomethacin (28 μM). Under control conditions, ATP (100 μM) infusion into the venule caused an increase in mean arteriolar diameter from 55 ± 4 to 78 ± 3 μm ( P < 0.05, n = 6). In the presence of indomethacin, mean resting arteriolar tone was not significantly altered (49 ± 4 μm), and the response to ATP was significantly attenuated (54 ± 4 μm, P < 0.05, n = 6). These studies show that increases in venular ATP concentrations stimulate the release of cyclooxygenase products, possibly from the venular endothelium, to vasodilate the adjacent arteriole.
Effects of diacetyl monoxime and cytochalasin D on ventricular fibrillation in swine right ventricles
Authors: Lee Moon-Hyoung , Lin Shien-Fong , Ohara Toshihiko , Omichi Chikaya , Okuyama Yuji , Chudin Eugene , Garfinkel Alan , Weiss James N. , Karagueuzian Hrayr S. , Chen Peng-Sheng
Published: December 2017

Whether or not the excitation-contraction (E-C) uncoupler diacetyl monoxime (DAM) and cytochalacin D (Cyto D) alter the ventricular fibrillation (VF) activation patterns is unclear. We recorded single cell action potentials and performed optical mapping in isolated perfused swine right ventricles (RV) at different concentrations of DAM and Cyto D. Increasing the concentration of DAM results in progressively shortened action potential duration (APD) measured to 90% repolarization, reduced the slope of the APD restitition curve, decreased Kolmogorov-Sinai entropy, and reduced the number of VF wave fronts. In all RVs, 15–20 mmol/l DAM converted VF to ventricular tachycardia (VT). The VF could be reinduced after the DAM was washed out. In comparison, Cyto D (10–40 μmol/l) has no effects on APD restitution curve or the dynamics of VF. The effects of DAM on VF are associated with a reduced number of wave fronts and dynamic complexities in VF. These results are compatible with the restitution hypothesis of VF and suggest that DAM may be unsuitable as an E-C uncoupler for optical mapping studies of VF in the swine RVs.
Selective attenuation by adenosine of arrhythmogenic action of isoproterenol on ventricular myocytes
Authors: Song Yejia , Shryock John C. , Knot Harm J. , Belardinelli Luiz
Published: December 2017

We examined whether adenosine equally attenuated the stimulatory effects of isoproterenol on arrhythmic activity and twitch shortening of guinea pig isolated ventricular myocytes. Transmembrane voltages and whole cell currents were recorded with patch electrodes, and cell twitch shortening was measured using a video-motion detector. Isoproterenol increased the action potential duration at 50% repolarization (APD50), L-type Ca2+ current [ I Ca(L)], and cell twitch shortening and induced delayed afterdepolarizations (DAD), transient inward current ( I Ti), and aftercontractions. Adenosine attenuated the arrhythmogenic actions of isoproterenol more than it attenuated the effects of isoproterenol on APD50, I Ca(L), or twitch shortening. Adenosine (0.1–100 μmol/l) decreased the amplitude of DADs by 30 ± 6% to 92 ± 5% but attenuated isoproterenol-induced prolongation of the APD50 by only 14 ± 4% to 59 ± 4% and had no effect on the voltage of action potential plateau. Adenosine (30 μmol/l) inhibited I Ti by 91 ± 4% but decreased isoproterenol-stimulated I Ca(L) by only 30 ± 12%. Isoproterenol-induced aftercontractions were abolished by adenosine (10 μmol/l), whereas the amplitude of twitch shortening was not reduced. The effects of adenosine on twitch shortenings and aftercontractions were mimicked by the A1-adenosine receptor agonist CPA ( N 6-cyclopentyladenosine) and by ryanodine. In conclusion, adenosine antagonized the proarrhythmic effect of β-adrenergic stimulation on ventricular myocytes without reducing cell twitch shortening.
Sympathetic restraint of respiratory sinus arrhythmia: implications for vagal-cardiac tone assessment in humans
Authors: Taylor J. Andrew , Myers Christopher W. , Halliwill John R. , Seidel Henrik , Eckberg Dwain L.
Published: December 2017

Clinicians and experimentalists routinely estimate vagal-cardiac nerve traffic from respiratory sinus arrhythmia. However, evidence suggests that sympathetic mechanisms may also modulate respiratory sinus arrhythmia. Our study examined modulation of respiratory sinus arrhythmia by sympathetic outflow. We measured R-R interval spectral power in 10 volunteers that breathed sequentially at 13 frequencies, from 15 to 3 breaths/min, before and after β-adrenergic blockade. We fitted changes of respiratory frequency R-R interval spectral power with a damped oscillator model: frequency-dependent oscillations with a resonant frequency, generated by driving forces and modified by damping influences. β-Adrenergic blockade enhanced respiratory sinus arrhythmia at all frequencies (at some, fourfold). The damped oscillator model fit experimental data well (39 of 40 ramps; r = 0.86 ± 0.02). β-Adrenergic blockade increased respiratory sinus arrhythmia by amplifying respiration-related driving forces ( P < 0.05), without altering resonant frequency or damping influences. Both spectral power data and the damped oscillator model indicate that cardiac sympathetic outflow markedly reduces heart period oscillations at all frequencies. This challenges the notion that respiratory sinus arrhythmia is mediated simply by vagal-cardiac nerve activity. These results have important implications for clinical and experimental estimation of human vagal cardiac tone.
Effect of removal of adventitia on vascular smooth muscle contraction and relaxation
Authors: González M. C. , Arribas S. M. , Molero F. , Fernández-Alfonso M. S.
Published: December 2017

The aim of the present study was to determine whether the adventitia of large arteries modulates vascular function. We developed a method to obtain functional vascular rings devoid of adventitia. Carotid and iliac arteries from 3-mo-old Sprague-Dawley rats were denuded from adventitia after treatment with collagenase followed by gentle peeling. Adventitia removal and integrity of the media was demonstrated by optical and confocal microscopy. Arterial rings with or without adventitia and with or without endothelium were mounted in an organ bath for isometric tension recording. Responses to 75 mM KCl or norepinephrine (0.1 nM–1 μM) were significantly reduced in segments without adventitia. Acetylcholine-induced relaxation (0.1 μM–0.1 mM) was enhanced in arteries without adventitia, whereas sodium nitroprusside-induced responses were not modified. These results demonstrate that the combination of stripping with a previous collagenase treatment allows us to obtain functional rings devoid of adventitia and that this layer plays a role in contractile capacity and in endothelium-modulated responses.
Free radical production in aortic rings from rats fed a fish oil-rich diet
Authors: López Diego , Caballero Catalina , Sánchez Juan , Puig-Parellada Pere , Mitjavila M. Teresa
Published: December 2017

To study the effect of the degree of unsaturation of dietary fatty acids on the production of free radicals and on the vascular smooth muscle tone in rings of the aorta, Sprague-Dawley rats were fed a semipurified diet containing 5% lipids from either corn oil (CO) or menhaden oil (MO) for 8 wk. The MO diet did not change the basal or NADPH-dependent superoxide anion (O[Formula: see text]·) release. There were no significant differences in phenylephrine-induced contractions between the two groups in intact rings. However, these contractions increased in endothelium-intact aortic rings from the MO group after addition of the nitric oxide (·NO) synthase inhibitor N G-nitro-l-arginine and in endothelium-denuded rings, both indicating a greater endothelial basal ·NO production in rats fed with the MO diet. Endothelium-dependent relaxations in response to acetylcholine were more prominent in rings from the MO group. These differences were not due to an increased smooth muscle response to ·NO, because relaxations were the same using an exogenous ·NO donor. Our results indicate that dietary MO did not modify O[Formula: see text]· release by the vessel wall or relaxation due to the cyclooxygenase pathway, but it potentiated endothelial production of ·NO.
Assessment of the time constant of relaxation: insights from simulations and hemodynamic measurements
Authors: De Mey S. , Thomas J. D. , Greenberg N. L. , Vandervoort P. M. , Verdonck P. R.
Published: December 2017

The objective of this study was to use high-fidelity animal data and numerical simulations to gain more insight into the reliability of the estimated relaxation constant derived from left ventricular pressure decays, assuming a monoexponential model with either a fixed zero or free moving pressure asymptote. Comparison of the experimental data with the results of the simulations demonstrated a trade off between the fixed zero and the free moving asymptote approach. The latter method more closely fits the pressure curves and has the advantage of producing an extra coefficient with potential diagnostic information. On the other hand, this method suffers from larger standard errors on the estimated coefficients. The method with fixed zero asymptote produces values of the time constant of isovolumetric relaxation (τ) within a narrow confidence interval. However, if the pressure curve is actually decaying to a nonzero pressure asymptote, this method results in an inferior fit of the pressure curve and a biased estimation of τ.
Endothelin-1 and nitric oxide synthase in short rebound reaction to short exposure to inhaled nitric oxide
Authors: Chen Luni , He Hao , Mondejar Enrique Fernandez , Fredén Filip , Wiklund Peter , Alving Kjell , Hedenstierna Göran
Published: December 2017

On withdrawal of inhalation of nitric oxide (INO) administered after lung injury, pulmonary artery pressure (PAP) and arterial oxygen tension (PaO2) may deteriorate more than before INO (rebound response). In this study, we investigated the possible roles of endothelin (ET)-1 and nitric oxide (NO) synthase (NOS) activity in the short rebound reaction to short-term inhalation of NO. Twenty-six anesthetized mechanically ventilated piglets were given endotoxin infusion. Twelve animals then received INO (30 parts per million) for two 30-min periods. Nine controls were not given NO. Measurements were made of blood gases and hemodynamic parameters, lung tissue ET-1 expression and NOS activity, and plasma ET-1 concentration. INO decreased PAP and increased PaO2, but INO withdrawal caused a short rebound reaction with an increase in PAP. Lung tissue expression and plasma concentration of ET-1 increased during INO, and plasma ET-1 increased further after its withdrawal. Activity of constitutive NOS decreased during INO, whereas that of inducible NOS was unchanged. Upregulation of ET-1 and downregulation of NOS activity may have influenced the short rebound reaction to short-term INO.
Catecholamines stimulate interleukin-6 synthesis in rat cardiac fibroblasts
Authors: Bürger Antje , Benicke Markus , Deten Alexander , Zimmer Heinz-Gerd
Published: December 2017

Proinflammatory cytokines have been implicated in the pathophysiology of different heart diseases. Recent evidence suggests that interleukin-6 (IL-6) may play a role in mechanisms leading to cardiac hypertrophy. In addition, catecholamines are known to induce cardiac hypertrophy. In the present study, we examined whether cardiac fibroblasts may be a potential source of IL-6 production in the rat heart and whether catecholamines can modulate the IL-6 synthesis. Only a small amount of IL-6 mRNA was detected in unstimulated rat cardiac fibroblasts. However, a 50-fold increase of IL-6 mRNA was found after stimulation with norepinephrine (NE). Addition of carvedilol, a α- and β-adrenergic receptor antagonist, prevented almost completely the NE-induced synthesis of IL-6 mRNA. Phenylephrine, an α-adrenergic agonist, and isoproterenol, a β-adrenergic agonist, also induced an increase in IL-6. However, the stimulation via β-receptors led to a more pronounced elevation. These data show that NE increases IL-6 expression in rat cardiac fibroblasts and that IL-6 may play an important autocrine/paracrine role in cardiac disease states associated with hypertrophy.
Differential effects of natriuretic peptides and NO on LV function in heart failure and normal dogs
Authors: Hart Chari Y. T. , Hahn Eugenia L. , Meyer Donna M. , Burnett John C. , Redfield Margaret M.
Published: December 2017

β-Adrenergic hyporesponsiveness in congestive heart failure (CHF) is mediated, in part, by nitric oxide (NO). NO and brain natriuretic peptide (BNP) share cGMP as a second messenger. Left ventricular (LV) function and inotropic response to intravenous dobutamine (Dob) were assessed during sequential intracoronary infusion of saline, HS-142-1 (a BNP receptor antagonist), and HS-142-1 + NG-monomethyl-l-arginine (l-NMMA) in anesthetized dogs with CHF due to rapid pacing and in normal dogs during intracoronary infusion of saline, exogenous BNP, and sodium nitroprusside (SNP). In CHF dogs, intracoronary HS-142-1 did not alter the inotropic response to Dob [percent change in first derivative of LV pressure (%ΔdP/d t) 47 ± 4% saline vs. 54 ± 7% HS-142-1, P = not significant]. Addition of intracoronary l-NMMA to HS-142-1 enhanced the response to Dob (%ΔdP/d t 73 ± 8% l-NMMA + HS-142-1, P < 0.05 vs. H142-1). In normal dogs, intracoronary SNP blunted the inotropic response to Dob (%ΔdP/d t 93 ± 6% saline vs. 71 ± 5% SNP, P < 0.05), whereas intracoronary BNP had no effect. In CHF dogs, the time constant of LV pressure decay during isovolumic relaxation increased with intracoronary HS-142-1 (48 ± 4 ms saline vs. 58 ± 5 ms HS-142-1, P < 0.05) and further increased with intracoronary l-NMMA (56 ± 6 ms HS-142-1 vs. 66 ± 7 ms l-NMMA + HS-142-1, P < 0.05). Endogenous BNP and NO preserve diastolic function in CHF, whereas NO but not BNP inhibits β-adrenergic responsiveness.
Lack of role for nitric oxide in cholinergic modulation of myocardial contractility in vivo
Authors: Crystal George J. , Zhou Xiping , Alam Syed , Piotrowski Agnieszka , Hu Guochang
Published: December 2017

Despite intensive investigation, the role of nitric oxide (NO) in cholinergic modulation of myocardial contractility remains unresolved. The left anterior descending coronary artery of 34 anesthetized, open-chest dogs was perfused via an extracorporeal circuit. Segmental shortening (SS) was measured with ultrasonic crystals and coronary blood flow (CBF) was measured with an ultrasonic flow transducer. An intracoronary infusion of ACh (20 μg/min) was performed, with CBF held constant, under baseline and during dobutamine, CaCl2, or amrinone at doses increasing SS by ∼50% (10 μg/min, 15 mg/min, and 300 μg/min ic, respectively). ACh-induced responses during dobutamine were also assessed following treatment with the NO synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME; 300 μg/min ic for 15 min). The effects of sodium nitroprusside (SNP; 80 μg/min ic), an exogenous NO donor, bradykinin (2.5 μg/min ic), a nonmuscarinic releaser of endothelial NO, and bilateral vagal stimulation (before and after l-NAME) were evaluated during dobutamine. ACh had no effect on SS under baseline or during CaCl2, but it decreased SS during dobutamine or amrinone (−23 ± 4% and −30 ± 5%, respectively). Vagal stimulation also reduced SS during dobutamine. l-NAME did not alter the ACh- or vagal-induced decreases in SS during dobutamine. Neither SNP nor bradykinin affected SS during dobutamine. In conclusion, ACh and vagal stimulation have a negative inotropic effect during stimulation of the β-adrenergic receptors that is independent of NO. The persistence of this effect during amrinone suggests that a mechanism downstream from adenylate cyclase is involved.
Protective effect of heat shock protein 72 on contractile function of perfused failing heart
Authors: Tanonaka Kouichi , Furuhama Ken-Ichi , Yoshida Hiroyuki , Kakuta Keiko , Miyamoto Yuki , Toga Wakako , Takeo Satoshi
Published: December 2017

The contribution of heat shock protein 72 (HSP72) to the protection of cardiac function was examined in rats with chronic heat failure (CHF) following coronary artery ligation (CAL). The CAL animals revealed functional deterioration without low cardiac output 2 wk after CAL and with low cardiac output 8 wk after CAL, suggesting that CHF had developed by 8 wk after CAL. The hearts isolated from animals 2 and 8 wk after CAL (2-wk CAL heart and 8-wk CAL heart, respectively) were subjected to hyperthermia (at 42°C) for 15 min, followed by 6-h perfusion (hyperthermia/6-h perfusion). The 2-wk CAL heart showed a 19.0 ± 3.9% decline in the rate- pressure product (RPP) after hyperthermia/6-h perfusion, similar to the nonoperated control (19.8 ± 2.9% decline). The production of myocardial HSP72 increased in the 2-wk CAL heart in response to hyperthermia (412.7 ± 29.5% of each prehyperthermia value). The 8-wk CAL heart showed a reduction in the RPP (45.2 ± 4.3% decline) after hyperthermia/6-h perfusion, associated with blunting of the production of HSP72 (68.9 ± 22.6% increase, respectively). The results suggest that functional deterioration of the isolated failing heart may be attributed to a reduction in the production of myocardial HSP72.
Effect of altered flow on the pattern of permeability around rabbit aortic branches
Authors: Staughton Tracey J. , Lever M. John , Weinberg Peter D.
Published: December 2017

Uptake of circulating macromolecules by the aortic wall is greater downstream than upstream of branch sites in immature rabbits, but the opposite pattern is seen at later ages. The mature pattern is nitric oxide dependent; we tested whether it is also flow dependent. Intercostal arteries of anesthetized rabbits were occluded, sham operated, or left alone. Uptake of rhodamine-labeled albumin was assessed by quantitative fluorescence microscopy of the sections through the aorta. In mature animals, uptake was higher upstream than downstream of the control and sham-operated branches, but the pattern was reversed at occluded branches. In young animals, uptake was not significantly different between regions upstream and downstream of control, sham-operated, or occluded branches. The absence of the normal immature pattern may reflect an influence of anesthesia and will assist in the elucidation of mechanisms underlying this pattern. The data for mature animals provide the first direct evidence that flow determines permeability near arterial branches and may account for the inverse spatial correlation between shear stress and disease prevalence at branches of adult human arteries.
Parathyroid hormone-related protein-(1-34) inhibits intrinsic pump activity of isolated murine lymph vessels
Authors: Mizuno Risuke , Ono Nobuyuki , Ohhashi Toshio
Published: December 2017

Parathyroid hormone-related protein (PTHrP) was originally found as a tumor-derived vasoactive factor and has also been known to produce significant relaxation of vascular smooth muscles. Thus effects of PTHrP-(1-34), a PTH receptor-binding domain, on spontaneous lymphatic pump activity was investigated in isolated pressurized lymph vessels of mice. Low concentrations (1 × 10−10 and 3 × 10−10 M) of PTHrP-(1-34) dilated lymph vessels and reduced the frequency of pump activity, whereas high concentrations (1 × 10−9 to 1 × 10−8 M) of PTHrP-(1-34) caused dilation with cessation of the lymphatic pump activity. N ω-nitro-l-arginine methyl ester (l-NAME; 3 × 10−5 M) but not indomethacin (1 × 10−5 M) significantly reduced the PTHrP-(1-34)-induced inhibitory responses of the lymphatic pump activity. In the presence of l-NAME (3 × 10−5 M) and l-arginine (1 × 10−3 M), the l-NAME-induced inhibition in the PTHrP-(1-34)-mediated responses was significantly reduced. Glibenclamide (1 × 10−6 M) significantly suppressed the inhibitory responses of the lymphatic pump activity induced by PTHrP-(1-34) and S-nitroso- N-acetyl-penicillamine. The PTHrP-(1-34)-mediated inhibitory responses were significantly reduced by treatment with PTHrP-(7-34) (1 × 10−7 M). These results suggest that PTHrP-(1-34) inhibits spontaneous pump activity of the isolated lymph vessels via PTH receptors and that production and release of endogenous nitric oxide and activation of ATP-sensitive K+ channels in the lymph vessels contribute to the PTHrP-(1-34)-mediated inhibitory responses of the lymphatic pump activity.
Regional septal dysfunction in a three-dimensional computational model of focal myofiber disarray
Authors: Usyk T. P. , Omens J. H. , McCulloch A. D.
Published: December 2017

MLC2v/ ras transgenic mice display a phenotype characteristic of hypertrophic cardiomyopathy, with septal hypertrophy and focal myocyte disarray. Experimental measurements of septal wall mechanics in ras transgenic mice have previously shown that regions of myocyte disarray have reduced principal systolic shortening, torsional systolic shear, and sarcomere length. To investigate the mechanisms of this regional dysfunction, a three-dimensional prolate spheroidal finite-element model was used to simulate filling and ejection in the hypertrophied mouse left ventricle with septal disarray. Focally disarrayed septal myocardium was modeled by randomly distributed three-dimensional regions of altered material properties based on measured statistical distributions of muscle fiber angular dispersion. Material properties in disarrayed regions were modeled by decreased systolic anisotropy derived from increased fiber angle dispersion and decreased systolic tension development associated with reduced sarcomere lengths. Compared with measurements in ras transgenic mice, the model showed similar heterogeneity of septal systolic strain with the largest reductions in principal shortening and torsional shear in regions of greatest disarray. Average systolic principal shortening on the right ventricular septal surface of the model was −0.114 for normal regions and −0.065 for disarrayed regions; for torsional shear, these values were 0.047 and 0.019, respectively. These model results suggest that regional dysfunction in ras transgenic mice may be explained in part by the observed structural defects, including myofiber dispersion and reduced sarcomere length, which contributed about equally to predicted dysfunction in the disarrayed myocardium.
Diminished α1-adrenergic-mediated contraction and translocation of PKC in senescent rat heart
Authors: Korzick D. H. , Holiman D. A. , Boluyt M. O. , Laughlin M. H. , Lakatta E. G.
Published: December 2017

Myocardial reserve function declines with aging due in part to reduced α- and β-adrenergic receptor (AR)-mediated contractile augmentation. Whereas specific age-associated deficits in β-AR signaling have been identified, it is not known which components of the α1-AR signaling cascade, e.g., protein kinase C (PKC) and associated anchoring proteins (receptors for activated C kinase; RACKs), underlie deficits in α1-AR contractile function with aging. We therefore assessed cardiac contraction (dP/d t) in Langendorff perfused hearts isolated from adult (5 mo) and senescent (24 mo) Wistar rats following maximal α1-AR stimulation with phenylephrine (PE), and we measured the subcellular distribution of PKCα and PKCε, and their respective anchoring proteins RACK1 and RACK2 by Western blotting. The maximum dP/d t response to PE (10−5M) was significantly reduced by 41% in 24-mo-old vs. 5-mo-old ( P < 0.01). Inhibitory effects of PKC blockade (chelerythrine; 10 μM) on dP/d t following α1-AR stimulation with PE observed in adult hearts were absent in 24-mo-old hearts ( P < 0.01). In 5-mo-old hearts, PE elicited reductions in soluble PKCα and PKCε levels, while increasing particulate PKCα and PKCε levels to a similar extent. In contrast, soluble PKCα and PKCε levels in 24-mo-old hearts were increased in response to PE; particulate PKCε and PKCα were unchanged or reduced and associated with significant reductions in particulate RACK1 and RACK2. The results indicate, for the first time, that selective translocation of PKCα and PKCε in response to α1-AR stimulation is disrupted in the senescent myocardium. That age-related reductions in particulate RACK1 and RACK2 levels were also observed provide evidence that alterations in PKC-anchoring proteins may contribute to impaired PKC translocation and defective α1-AR contraction in the aged rat heart.
Inotropic response of rabbit ventricular myocytes to endothelin-1: difference from isolated papillary muscles
Authors: Talukder M. A. Hassan , Norota Ikuo , Sakurai Kiyoharu , Endoh Masao
Published: December 2017

Endothelin-1 (ET-1) increased cell shortening and Ca2+ transients over the concentration of 3 × 10−11 M to 10−9 M with EC50 of 8.3 × 10−11 M in rabbit single ventricular myocytes. Thus ET-1 was approximately 60 times more potent in single myocytes than in papillary muscles (EC50 = 5.1 × 10−9 M) of the same species. In single myocytes, ET-1 at 10−8 M elicited an inhibitory response that counteracted the facilitatory response: the concentration-response curve (CRC) for ET-1 was bell shaped. The ETA-receptor antagonist BQ-485 shifted CRC for ET-1 to the right in parallel; however, the facilitatory response to 10−8 M ET-1 was markedly enhanced by BQ-485 and also by the ETB antagonist BQ-788. The ETA/ETB antagonist TAK-044 abolished the ET-1-induced response. These findings indicate that the response to ET-1 of single myocytes is different from that of papillary muscles in concentration dependence, characteristics of the response, and susceptibility to ET-receptor antagonists. Anomalous pharmacological characteristics of ET-1-induced response in rabbit papillary muscles may be due to integrated regulatory mechanisms that may involve also various types of noncardiac cell in ventricular myocardium.
Role of endothelial [Ca2+]iin activation of eNOS in pressurized arterioles by agonists and wall shear stress
Authors: Ungvari Zoltan , Sun Dong , Huang An , Kaley Gabor , Koller Akos
Published: December 2017

In cultured endothelial cells, Ca2+-dependent and -independent activation of nitric oxide (NO) synthesis to agonists and flow/wall shear stress (WSS) has been demonstrated. However, the presence and function of these pathways are less well known in microvessels that can be exposed to a high level of WSS. We hypothesized that the role of changes in endothelial intracellular calcium concentration ([Ca2+]i) is different in agonist- and WSS-induced release of NO. Thus changes in endothelial [Ca2+]iand diameter of intact pressurized (∼100 μm at 80 mmHg) gracilis skeletal muscle arterioles of rats were measured by fluorescent videomicroscopy. Acetylcholine (ACh) and increases in WSS (by increasing intraluminal flow) elicited dilations (maximum 91 ± 2% and 34 ± 4%) that could be inhibited by Nω-nitro-l-arginine methyl ester (l-NAME), a NO synthase blocker. In diameter-clamped arterioles, ACh caused substantial increases in the endothelial calcium fluorescence ratio (ERCa, maximum 43 ± 5%), which was significantly greater than changes in ERCa(maximum ∼10%) to increases in WSS. The Ca2+ionophore A-23187 also substantially increased ERCa(maximum 38 ± 5%) and elicited significant l-NAME-sensitive arteriolar dilations (maximum 45 ± 7%). Intraluminal administration of the tyrosine kinase inhibitor genistein had no effect on dilations induced by ACh or the NO donor sodium nitroprusside, whereas it eliminated WSS-induced dilations. Collectively, our data suggest that, in endothelium of skeletal muscle arterioles, NO synthesis is activated by shear stress without a substantial increase in [Ca2+]i, most likely by activation of tyrosine kinase pathways, whereas NO release by ACh and A-23187 is associated with substantial increases in [Ca2+]i.
Effects of κ-opioid receptor activation on myocardium
Authors: Pyle W. G. , Lester J. W. , Hofmann P. A.
Published: December 2017

κ-Opioid receptor stimulation of the heart transiently increases twitch amplitude and decreases Ca2+-dependent actomyosin Mg2+-ATPase activity through an undetermined mechanism. One purpose of the present study was to determine if the increase in twitch amplitude is due to changes in myofilament Ca2+sensitivity. We also wanted to determine if κ-opioid receptor activation alters maximum actin-myosin ATPase activity and Ca2+sensitivity of tension in a way consistent with protein kinase A or protein kinase C (PKC) action. Rat hearts were treated with U50,488H (a κ-opioid receptor agonist), phenylephrine plus propranolol (α-adrenergic receptor stimulation), isoproterenol (a β-adrenergic receptor agonist), or phorbol 12-myristate 13-acetate (PMA, receptor independent activator of PKC) or were untreated (control), and myofibrils were isolated. U50,488H, phenylephrine plus propranolol, and PMA all decreased maximum Ca2+-dependent actomyosin Mg2+-ATPase activity, whereas isoproterenol treatment increased maximum Ca2+-dependent actomyosin Mg2+- ATPase activity. Untreated myofibrils exposed to exogenous PKC-ε, but not PKC-δ, decreased maximum actomyosin Mg2+-ATPase activity. Langendorff-perfused hearts treated with U50,488H, phenylephrine plus propranolol, or isoproterenol had significantly higher ventricular ATP levels compared with control hearts. PKC inhibitors abolished the effects of U50,488H on Ca2+-dependent actomyosin Mg2+-ATPase activity and myocardial ATP levels. U50,488H and PMA treatment of isolated ventricular myocytes increased Ca2+sensitivity of isometric tension compared with control myocytes at pH 7.0. The U50,488H-dependent increase in Ca2+sensitivity of tension was retained at pH 6.6. Together, these findings are consistent with the hypotheses that 1) the positive inotropy associated with κ-opioid receptor activation may be due in part to a PKC-mediated increase in myofilament Ca2+-sensitivity of tension and 2) the κ-opioid receptor-PKC pathway is a modulator of myocardial energy status through reduction of actomyosin ATP consumption.
Alterations of Ca2+mobilizing properties in migrating endothelial cells
Authors: Kimura Chiwaka , Oike Masahiro , Koyama Tetsuya , Ito Yushi
Published: December 2017

Endothelial migration is one of the major events of pathological neovascularization. We compared the characteristics of Ca2+mobilization in nonconfluent, confluent, and migrating endothelial cells. Migration of endothelial cells was induced by wounding the confluent cell monolayer. The basal intracellular Ca2+concentration was lower in migrating cells and higher in confluent cells than in nonconfluent cells. Thapsigargin (TG)-induced Ca2+leak and TG-evoked Ca2+entry were accelerated in migrating cells, whereas the latter was suppressed in confluent cells. The ATP-induced Ca2+transient was also much larger in migrating cells than in confluent cells. These alterations were also observed in a cell as an intracellular polarization, i.e., the leading edge showed an acceleration of TG-evoked Ca2+entry and an augmentation of the ATP-induced Ca2+transient. Endothelial migration was significantly suppressed by TG or cyclopiazonic acid. These observations suggest that the alterations of Ca2+store site-related Ca2+mobilizations, i.e., Ca2+sequestration, release, and TG-evoked Ca2+entry, may be involved in the cellular mechanisms of endothelial migration.
Mechanism of uterine vascular refractoriness to endothelin-1 in pregnant sheep
Authors: McElvy Sherrie , Greenberg Suzanne G. , Mershon John L. , Yang Da Seng , Magill Catherine , Clark Kenneth E.
Published: December 2017

Endothelin-1 (ET-1) is a potent vasoconstrictor and produces marked pressor responses when given systemically. Studies in sheep have demonstrated that during pregnancy the uterine vasculature is refractory to exogenously administered ET-1. We hypothesize that this pregnancy-dependent refractoriness is due to an upregulation of local uterine metabolism of ET-1 and/or ETBreceptors and/or downregulation of local uterine ETAreceptors. To investigate these possibilities, 21 nonpregnant and 17 pregnant sheep were used. Dose-response curves to intravenous infusion of ET-1 and phenylephrine were generated for pregnant and nonpregnant sheep. ET-1 infused systemically demonstrated vasoconstriction in the systemic and renal vasculature of pregnant and nonpregnant animals and vasoconstriction in the uterine vasculature of nonpregnant animals. The pregnant animals showed no uterine vascular response to ET-1. In contrast, phenylephrine showed vasoconstriction in the systemic, renal, and uterine circulations in both pregnant and nonpregnant sheep. After experimentation, the animals were euthanized, and tissues were harvested for Western blot and activity analysis of neutral endopeptidase (NEP) or RT-PCR analysis of endothelin-converting enzyme (ECE) and ETA and ETB receptors. The content and activity of NEP in the uterine and renal vasculature of pregnant and nonpregnant animals were similar. RT-PCR demonstrated the presence of ECE in the uterine vasculature of pregnant and nonpregnant sheep. ETA receptor mRNA was significantly reduced in pregnant compared with nonpregnant sheep, whereas ETB receptor mRNA remained unchanged. We conclude that the uterine vascular refractoriness seen in the pregnant sheep is due to a downregulation of ETA receptors.
Right ventricular oxygen supply/demand balance in exercising dogs
Authors: Hart Bradley J. , Bian Xiaoming , Gwirtz Patricia A. , Setty Srinath , Downey H. Fred
Published: December 2017

This is the first investigation of right ventricular (RV) myocardial oxygen supply/demand balance in a conscious animal. A novel technique developed in our laboratory was used to collect right coronary (RC) venous blood samples from seven instrumented, conscious dogs at rest and during graded treadmill exercise. Contributions of the RV oxygen extraction reserve and the RC flow reserve to exercise-induced increases in RV oxygen demand were measured. Strenuous exercise caused a 269% increase in RV oxygen consumption. Expanded arteriovenous oxygen content difference (A-VΔO2) provided 58% of this increase in oxygen demand, and increased RC blood flow (RCBF) provided 42%. At less strenuous exercise, expanded A-VΔO2provided 60–80% of the required oxygen, and increases in RCBF were small and driven by increased aortic pressure. RC resistance fell only at strenuous exercise after the extraction reserve had been mobilized. Thus RC resistance was unaffected by large decreases in RC venous Po2until an apparent threshold at 20 mmHg was reached. Comparisons of RV findings with published left ventricular data from exercising dogs demonstrated that increased O2demand of the left ventricle is met primarily by increasing coronary flow, whereas increased O2extraction makes a greater contribution to RV O2supply.
Hemodynamic effects elicited by microinjection of glutamatergic agonists into NTS of conscious rats
Authors: Rodrigues Dias Ana Carolina , Talman William T. , Colombari Eduardo
Published: December 2017

In this study, we characterized the arterial pressure, heart rate, and regional vascular conductance responses elicited by unilateral microinjection of ionotropic glutamatergic agonists N-methyl-d-aspartic acid (NMDA and non-NMDA) into the nucleus of tractus solitarius (NTS) of conscious rats. Microinjections of NMDA and S-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) caused changes in mean arterial pressure (MAP). Lower doses elicited decreases in MAP, whereas higher doses elicited biphasic responses (decreases followed by increases). Both agonists induced bradycardia and elicited dose-dependent vasoconstriction in the renal, mesenteric, and hindquarter beds. AMPA elicited delayed vasodilation in the hindquarter bed but NMDA did not. Bradycardia and initial hypotension produced by each agonist were abolished by systemic administration of the muscarinic antagonist methylatropine. However, methylatropine did not affect either the vasoconstriction or the vasodilatation. The contrasting hemodynamic effects produced by NMDA and AMPA could be caused by activation of differential subsets of NTS neurons. Preferential activation of one subset could produce the NMDA-related responses, whereas activation of another subset would elicit AMPA-related responses.
KVα1 channels in murine arterioles: differential cellular expression and regulation of diameter
Authors: Cheong A. , Dedman A. M. , Xu S. Z. , Beech D. J.
Published: December 2017

The primary objectives of this study were to reveal cell-specific expression patterns and functions of voltage-gated K+channel (KVα1) subunits in precapillary arterioles of the murine cerebral circulation. KVα1 were detected using peptide-specific antibodies in immunofluorescence and Western blotting assays. KV1.2 was localized almost exclusively to endothelial cells, whereas KV1.5 was discretely localized to the nerves and nerve terminals that innervate the arterioles. KV1.5 also localized specifically to arteriolar nerves in human pial membrane. KV1.5 was notable for its absence from smooth muscle cells. KV1.3, KV1.4, and KV1.6 were localized to endothelial and smooth muscle cells, although KV1.4 had a low expression level. KV1.1 was not expressed. Therefore, we show that different cell types of pial arterioles have distinct physiological expression profiles of KVα1, conferring the possibility of differential modulation by extracellular and second messengers. Furthermore, we show recombinant agitoxin-2 and margatoxin are potent vasoconstrictors, suggesting that KVα1 subunits have a major function in determining arteriolar resistance to blood flow.
Preserved contractile function despite atrophic remodeling in unloaded rat hearts
Authors: Welsh Denise C. , Dipla Konstantina , McNulty Patrick H. , Mu Anbin , Ojamaa Kaie M. , Klein Irwin , Houser Steven R. , Margulies Kenneth B.
Published: December 2017

The present study was designed to determine whether myocardial atrophy is necessarily associated with changes in cardiac contractility. Myocardial unloading of normal hearts was produced via heterotopic transplantation in rats. Contractions of isolated myocytes (1.2 mM Ca2+; 37°C) were assessed during field stimulation (0.5, 1.0, and 2.0 Hz), and papillary muscle contractions were assessed during direct stimulation (2.0 mM Ca2+; 37°C; 0.5 Hz). Hemodynamic unloading was associated with a 41% decrease in median myocyte volume and proportional decreases in myocyte length and width. Nevertheless, atrophic myocytes had normal fractional shortening, time to peak contraction, and relaxation times. Despite decreases in absolute maximal force generation (Fmax), there were no differences in Fmax/ area in papillary muscles isolated from unloaded transplanted hearts. Therefore, atrophic remodeling after unloading is associated with intact contractile function in isolated myocytes and papillary muscles when contractile indexes are normalized to account for reductions in cell length and cross-sectional area, respectively. Nevertheless, in the absence of compensatory increases in contractile function, reductions in myocardial mass will lead to impaired overall work capacity.
Role of smooth muscle cells on endothelial cell cytosolic free calcium in porcine coronary arteries
Authors: Budel Stéphane , Schuster Alexander , Stergiopoulos Nikos , Meister Jean-Jacques , Bény Jean-Louis
Published: December 2017

We tested the hypothesis that the cytosolic free calcium concentration in endothelial cells is under the influence of the smooth muscle cells in the coronary circulation. In the left descending branch of porcine coronary arteries, cytosolic free calcium concentration ([Ca2+]i) was estimated by determining the fluorescence ratio of two calcium probes, fluo 4 and fura red, in smooth muscle and endothelial cells using confocal microscopy. Acetylcholine and potassium, which act directly on smooth muscle cells to increase [Ca2+]i, were found to indirectly elevate [Ca2+]i in endothelial cells; in primary cultures of endothelial cells, neither stimulus affected [Ca2+]i, yet substance P increased the fluorescence ratio twofold. In response to acetylcholine and potassium, isometric tension developed by arterial strips with intact endothelium was attenuated by up to 22% ( P < 0.05) compared with strips without endothelium. These findings suggest that stimuli that increase smooth muscle [Ca2+]i can indirectly influence endothelial cell function in porcine coronary arteries. Such a pathway for negative feedback can moderate vasoconstriction and diminish the potential for vasospasm in the coronary circulation.