bluuebunny/crossref_metadata_2025 huggingface dataset:
Mouse and rat plasma renin concentration and gene expression in (mRen2)27 transgenic rats
Authors: Bohlender Jürgen , Ménard Joel , Edling Oliver , Ganten Detlev , Luft Friedrich C.
Published: December 2017

The (mRen2)27 transgenic rat [TGR(mRen2)27] is said to have low plasma levels of active renin. We used a direct radioimmunoassay (RIA) for mouse submaxillary renin, as well as an indirect enzyme-kinetic assay based on the generation of angiotensin I with modification of the pH optimum, to measure rat and mouse plasma renin activity (PRA), plasma renin concentration (PRC), and plasma prorenin in TGR before and after lisinopril. The relationship between rat PRC and %rat kidney extract was steepest at pH 6.0 and flat at pH 8.5, whereas the relationship between mouse PRC and purified mouse renin was steepest at pH 8.5 and flat at pH 6.0. Mouse PRC was highly correlated with direct RIA measurements ( r = 0.93). PRA before lisinopril was little influenced by pH, whereas the increase with lisinopril was greatest at pH 6.5. PRC before lisinopril was fourfold higher at pH 8.5 compared with that at pH 6.0. Lisinopril increased both PRC values but reversed the pH dependency. Prorenin was fourfold higher at pH 8.5 compared with that at pH 6.0 and decreased slightly with lisinopril. Renal renin concentration was higher at pH 6.0 than at pH 8.5. With lisinopril, renal renin concentration increased at both pH values. Mouse PRC was not changed by lisinopril. Ribonuclease protection assay showed both rat and mouse renin gene expression in the kidney, which increased with lisinopril. Thus TGR have circulating active rat and mouse renin and prorenin. The notion that TGR are a “low renin” model should be revised.
Endogenous calcitonin gene-related peptide modulates tachycardiac but not bradycardiac baroreflex in rats
Authors: Kim Seungbum , Ouchi Yasuyoshi , Sekiguchi Hiromichi , Fujikawa Hideyuki , Shimada Kazuyuki , Yagi Kinji
Published: December 2017

Effects of intracisternally administered human calcitonin gene-related peptide (8-37) [hCGRP-(8—37)], an antagonist, and hCGRP, an agonist of the CGRP receptor in the rat central nervous system, on baroreflex sensitivity (BRS) were studied in conscious male rats. Each rat sequentially received intracisternally injected 0.9% saline and then hCGRP-(8—37) at doses of 1, 2.5, and 5 nmol in a volume of 10 μl at an interval of 15 min. Five minutes after each injection, sodium nitroprusside (SNP, 10 μg/kg) or phenylephrine hydrochloride (PE, 2 μg/kg) was intravenously administered to induce reflex tachycardia or bradycardia, respectively. Intracisternally administered hCGRP-(8—37) increased BRS of the reflex tachycardia induced by SNP in a dose-related manner but did not change the BRS after PE. Intracisternally injected hCGRP significantly decreased the BRS after SNP. The lowering effect of hCGRP on BRS after SNP was inhibited by hCGRP-(8—37) injected before hCGRP. These results suggest that endogenous CGRP in the lower brain stem is selectively involved in the tachycardiac but not the bradycardiac baroreflex and modulates the baroreflex in an inhibitory rather than facilitatory fashion.
Adenosine depletion alters postictal hypoxic cerebral vasodilation in the newborn pig
Authors: DiGeronimo R. J. , Gegg C. A. , Zuckerman S. L.
Published: December 2017

Altered postictal cerebral blood flow dilatory responses may contribute to brain injury following neonatal seizures. We developed an initial series of experiments to characterize the effects of seizure activity on cerebral vascular dilatory responses during the immediate postictal period. Significant attenuation of postictal hypoxic cerebral vasodilation was noted. We hypothesize that this diminished cerebral dilator response to hypoxia involves depletion of adenosine (Ado) activity resulting from seizure ictus. Additional experiments were designed to evaluate whether the altered postictal responses were related to a depletion of Ado stores or a decreased response to Ado in the postictal state. Farm-bred piglets were equipped with closed cranial windows. Responses to hypercapnia (10% CO2), hypoxia (fractional inspired O2 = 0.10), and topical sodium nitroprusside (10−6M) were compared before and after bicuculline-induced seizures (1 mg/kg). Hypoxia-induced cerebral vasodilation was significantly attenuated in the first 90 min postictal (control: 56.5 ± 6%, 10 min postictal: 6.3 ± 2%, 60 min postictal: 21.7 ± 6%, and 90 min postictal: 21.6 ± 5%; P < 0.01), whereas the dilator responses to hypercapnia and topical sodium nitroprusside remained intact. In a separate group of piglets, both a dilating (10−5 M) and a nondilating concentration of Ado (10−11 M) were topically administered postictally to measure their effects on pial vessel dilatory response to hypoxia. Dilation to topical Ado (10−5 M) was not altered postictally compared with control. Ado (10−11 M) restored hypoxia-induced vasodilation to preseizure control values in the immediate postictal period (control: 51.0 ± 8%, postictal: 46.7 ± 8%; P > 0.05). Postictal administration of Ado will restore hypoxia-induced cerebral vasodilation in piglets even when a nondilating concentration is employed. This suggests that depletion of Ado with seizure activity is a mechanism for the loss of postictal cerebral vasodilation to hypoxia, and the role of Ado in hypoxic cerebral vasodilation is permissive.
Gene-targeted mice reveal importance of L-selectin-dependent rolling for neutrophil adhesion
Authors: Jung Unsu , Ramos Carroll L. , Bullard Daniel C. , Ley Klaus
Published: December 2017

It has not been determined whether L-selectin-mediated rolling can promote leukocyte adhesion in vivo independent of P- and E-selectin. We used intravital microscopy of E- and P-selectin double-mutant mice (E−/P−) stimulated with tumor necrosis factor-α for 6–8 h to investigate the importance of L-selectin-dependent rolling in cremaster muscle venules. Rolling leukocyte flux in E−/P− mice was 9 ± 2 cells/min compared with 77 ± 17 cells/min in wild-type (WT) mice. Pretreatment with the L-selectin monoclonal antibody MEL-14 significantly reduced rolling in both E−/P− (by 89%) and WT mice (by 79%). L-selectin-dependent rolling in E−/P− mice resulted in leukocyte adhesion comparable to that seen in WT mice. MEL-14 pretreatment of E−/P− mice reduced leukocyte adhesion by 50%. The majority (∼80%) of intravascular leukocytes in both WT and E−/P− mice were neutrophils. We conclude that L-selectin can mediate rolling that results in sufficient leukocyte recruitment to account for the robust inflammatory response seen in E−/P− mice at later times.
Vasopressin acts in the area postrema to attenuate the exercise pressor reflex in anesthetized cats
Authors: Stebbins Charles L. , Bonigut Stefani , Liviakis Lea R. , Munch Paul A.
Published: December 2017

Circulating arginine vasopressin (AVP) can enhance baroreflex function via its action in the area postrema (AP). We tested the hypothesis that AVP acts in the AP to enhance baroreflex function during static contraction and, in turn, attenuates the exercise pressor reflex. Thus mean arterial blood pressure ( n = 9) and heart rate (HR) ( n = 9) during 30 s of electrically stimulated hindlimb contraction were compared before and after bilateral microinjections of 200 nl of the AVP V1-receptor antagonist d(CH2)5Tyr(Me)-AVP (V1x) (1 ng/nl) into the AP of the anesthetized cat. This protocol was repeated in three other cats in which sinoaortic denervation (SAD) was performed before any intervention. Injection of V1xinto the AP had no effect on baseline blood pressure or HR. However, pressor and HR responses to static contraction were augmented by 44 ± 10 and 29 ± 9%, respectively. Static contraction also increased plasma AVP from 15.9 ± 2.0 to 25.5 ± 3.4 pg/ml. In the SAD cats, microinjection of V1x had no effect on contraction-induced increases in blood pressure or HR. These results suggest that baroreflex opposition of the reflex cardiovascular response to static contraction is enhanced by the action of AVP in the AP.
Increased expression of eukaryotic initiation factor 4E during growth of neonatal rat cardiocytes in vitro
Authors: Makhlouf Antoine A. , McDermott Paul J.
Published: December 2017

Eukaryotic initiation factor 4E (eIF-4E) is rate limiting for translational initiation. The purpose of this study was to determine whether eIF-4E levels are increased during cardiocyte growth produced by increased load in the form of electrically stimulated contraction. Neonatal rat cardiocytes were cultured on a matrix of aligned type I collagen. The cardiocytes aligned in parallel to the direction of the collagen fibrils and exhibited an elongated, rod-shaped morphology. Cardiocytes were electrically stimulated to contract at 3 Hz (alternating polarity, 5-ms pulse width). Nonstimulated cardiocytes were quiescent and used as controls. Electrically stimulated contraction produced hypertrophic growth as determined by the following criteria: 1) increased protein content, 2) increased RNA content, 3) accelerated rate of protein synthesis, and 4) threefold increase in promoter activity of the atrial natriuretic factor gene. Cardiocyte growth was associated with an increase in eIF-4E mRNA levels that reached 48 ± 9% after 2 days of electrically stimulated contraction. eIF-4E protein levels were increased by more than twofold over the same time period. We conclude that an adaptive increase in eIF-4E is an important mechanism for maintaining translational efficiency during cardiocyte growth.
Electrical interactions between a rabbit atrial cell and a nodal cell model
Authors: Joyner Ronald W. , Kumar Rajiv , Golod David A. , Wilders Ronald , Jongsma Habo J. , Verheijck E. Etienne , Bouman Lennart , Goolsby William N. , Van Ginneken Antoni C. G.
Published: December 2017

Atrial activation involves interactions between cells with automaticity and slow-response action potentials with cells that are intrinsically quiescent with fast-response action potentials. Understanding normal and abnormal atrial activity requires an understanding of this process. We studied interactions of a cell with spontaneous activity, represented by a “real-time” simulation of a model of the rabbit sinoatrial (SA) node cell, simultaneously being electrically coupled via our “coupling clamp” circuit to a real, isolated atrial myocyte with variations in coupling conductance ( Gc) or stimulus frequency. The atrial cells were able to be driven at a regular rate by a single SA node model (SAN model) cell. Critical Gcfor entrainment of the SAN model cell to a nonstimulated atrial cell was 0.55 ± 0.05 nS ( n = 7), and the critical Gcthat allowed entrainment when the atrial cell was directly paced at a basic cycle length of 300 ms was 0.32 ± 0.01 nS ( n = 7). For each atrial cell we found periodic phenomena of synchronization other than 1:1 entrainment when Gcwas between 0.1 and 0.3 nS, below the value required for frequency entrainment, when the atrial cell was directly driven at a basic cycle length of either 300 or 600 ms. In conclusion, the high input resistance of the atrial cells allows successful entrainment of nodal and atrial cells at low values of Gc, but further uncoupling produces arrhythmic interactions.
Discordant S-T alternans contributes to formation of reentry: a possible mechanism of reperfusion arrhythmia
Authors: Tachibana Hidetada , Kubota Isao , Yamaki Michiyasu , Watanabe Tetsu , Tomoike Hitonobu
Published: December 2017

Although a relationship between S-T alternans and life-threatening arrhythmia has been recognized, the mechanism is poorly understood. We examine the role of S-T alternans in the occurrence of ventricular fibrillation (VF) after reperfusion. The left anterior descending coronary artery was occluded for 20 min and then abruptly reperfused in 12 intravenously anesthetized open-chest dogs. Sixty unipolar epicardial electrograms were recorded during the control state, at the end of occlusion, and after reperfusion. The largest magnitude of S-T alternans among 60 leads was defined as the maximum S-T alternans. Isochronal maps of activation time in paced beat and spontaneous ventricular premature contractions (VPC) were analyzed. After reperfusion, VF ensued in six dogs. The maximum S-T alternans augmented progressively with time after reperfusion until VF occurred. In three dogs with VF, when activation of VPC resulted in conduction block and formed reentry, VF ensued. The conduction block was located between sites of discordant S-T alternans (S-T alternans at adjacent leads was out of phase). These data indicate that discordant S-T alternans relates to VF by facilitating the formation of a reentrant circuit.
Chloride ion currents contribute functionally to norepinephrine-induced vascular contraction
Authors: Lamb Fred S. , Barna Thomas J.
Published: December 2017

Norepinephrine (NE) increases Cl− efflux from vascular smooth muscle (VSM) cells. An increase in Cl− conductance produces membrane depolarization. We hypothesized that if Cl− currents are important for agonist-induced depolarization, then interfering with cellular Cl− handling should alter contractility. Isometric contraction of rat aortic rings was studied in a bicarbonate buffer. Substitution of extracellular Cl− with 130 mM methanesulfonate (MS; 8 mM Cl−) did not cause contraction. NE- and serotonin-induced contractions were potentiated in this low-Cl− buffer, whereas responses to K+, BAY K 8644, or NE in the absence of Ca2+ were unaltered. Substitution of Cl− with I− or Br− suppressed responses to NE. Inhibition of Cl−transport with bumetanide (10−5 M) or bicarbonate-free conditions (10 mM HEPES) inhibited NE- but not KCl-induced contraction. The Cl−-channel blockers DIDS (10−3 M), anthracene-9-carboxylic acid (10−3 M), and niflumic acid (10−5 M) all inhibited NE-induced contraction, whereas tamoxifen (10−5 M) did not. Finally, disruption of sarcoplasmic reticular function with cyclopiazonic acid (10−7 M) or ryanodine (10−5 M) prevented the increase in the peak response to NE produced by low-Cl− buffer. We conclude that a Cl− current with a permeability sequence of I−> Br− > Cl− > MS is critical to agonist-induced contraction of VSM.
Cytokine expression increases in nonmyocytes from rats with postinfarction heart failure
Authors: Yue Ping , Massie Barry M. , Simpson Paul C. , Long Carlin S.
Published: December 2017

Growing evidence suggests that cardiac nonmyocyte cells may play an important regulatory role in the response to myocardial overload and injury via altered expression of paracrine products, such as cytokines and growth factors, but information concerning the cell-specific changes in the expression of these substances in heart-failure models is limited. Therefore, cardiac nonmyocytes were isolated from rats 1 day and 1 and 6 wk after left coronary artery ligation with resulting hemodynamic evidence of heart failure and in sham-operated control animals. mRNAs for tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, transforming growth factors (TGF)-β1 and TGF-β3, and type I and type III collagen were measured by Northern analyses. The temporal and quantitative relationships between the expression of these cytokines and collagen and myocyte hypertrophy were determined. mRNA expression of IL-1β was increased by 1.3-fold at 1 day and 1 wk, and expression of TNF-α, IL-1β, IL-6, TGF-β1, and TGF-β3 were increased by 1.4- to 2.1-fold at the 1-wk time point before returning toward baseline at 6 wk. There were significant correlations between the expression of these cytokines and the expression of types I and III collagen, which also peaked at 1 wk. Myocyte hypertrophy was seen first at 6 wk. These observations are consistent with a hypothesis that nonmyocyte cells play a regulatory role in the extracellular matrix changes during postinfarction remodeling and highlight the importance of examining cell-specific changes in gene expression and elucidating the role of cell-to-cell interactions within the myocardium.
Nonlinear interactions of slow and rapid rhythms in sympathetic nerve discharge
Authors: Zhong Sheng , Gebber Gerard L. , Zhou Shi-Yi , Barman Susan M.
Published: December 2017

We used bispectral analysis to characterize the nonlinear interactions of the respiratory-related (RR), cardiac-related (CR), or 10-Hz rhythms in sympathetic nerve discharge (SND) of urethan-anesthetized cats. Bispectral analysis investigates relationships among frequency triples in the same signal (inferior cardiac postganglionic SND) where the third frequency is the sum of the other two due to quadratic nonlinear coupling. Coupling of the RR and CR rhythms leading to the generation of new components (i.e., modulated frequencies) in SND occurred in 84% of the total cases, whereas the incidence was 71% for the RR and 10-Hz rhythms. The occurrence of such nonlinear interactions implies that the RR, CR, and 10-Hz rhythms are carried to common targets by the same postganglionic sympathetic neurons. Furthermore, we suggest that nonlinear interactions leading to the generation of new frequencies in SND may affect end-organ function beyond the level expected in simple cases of linear superposition of the primary rhythms. This suggestion is supported by our observation that strong coupling of the RR and CR rhythms resulted in appreciable power at the modulated frequencies.
Nitric oxide modulates gut ischemia-reperfusion-induced P-selectin expression in murine liver
Authors: Horie Yoshinori , Wolf Robert , Anderson Donald C. , Granger D. Neil
Published: December 2017

Reperfusion of ischemic intestine is associated with P-selectin-dependent adhesion of leukocytes in the liver microcirculation. The objective of this study was to define the contribution of nitric oxide (NO) to the enhanced P-selectin expression and increased leukocyte rolling elicited by gut ischemia-reperfusion (I/R). Leukocyte rolling (monitored by intravital microscopy) in the terminal hepatic venules (THV) and P-selectin expression (measured using the dual-radiolabeled monoclonal antibody technique) were determined in mice after 15 min of superior mesenteric artery occlusion and 30 min of reperfusion. After 30 min of reperfusion, P-selectin expression was significantly increased in the liver, intestine, and lung, with a corresponding increase in the number of rolling leukocytes (in THV). The NO synthase inhibitor NG-monomethyl-l-arginine exaggerated the gut I/R-induced increases in both rolling leukocytes and P-selectin expression (in liver and intestine), responses that were not detected with coadministration ofl-arginine or in P-selectin-deficient mice. The NO donor diethylenetriamine/NO andl-arginine were both effective in attenuating the gut I/R-induced increases in rolling leukocytes (in THV) and P-selectin expression (in liver, intestine, and lung). These findings indicate that NO modulates gut I/R-induced recruitment of rolling leukocytes in THV via an action on P-selectin expression.
Fos response of fetal sheep anterior circumventricular organs to osmotic challenge in late gestation
Authors: McDonald T. J. , Li C. , Nijland M. J. M. , Caston-Balderrama A. , Ross M. G.
Published: December 2017

We hypothesized that the anterior circumventricular organs (ACVO) and the supraoptic (SON) and hypothalamic paraventricular nuclei (PVN), among other structures that play a role in sensing extracellular body fluid volume and composition in postnatal animals (as demonstrated by Fos protein production by the immediate-early gene c- fos), would show similar activation in fetal sheep during an osmotic challenge. The brains of 10 fetal sheep [6 treated, 4 controls; 129–131 days of gestational age (dGA) = 0.87 gestation] were immunostained for Fos. Seventy-five minutes before tissue collection the dams were given intravenous 20% mannitol (1 ml ⋅ min−1 ⋅ kg−1for 10 min). Subsequently, the ACVO, SON, and PVN were scored for the amount of neuronal Fos immunostaining. The subfornical organ (SFO; 24.5 ± 9.0 vs. 1.7 ± 1.2), the organum vasculosum of the lamina terminalis (OVLT; 26.8 ± 5.6 vs. 7.0 ± 2.0), the SON (39.8 ± 3.0 vs. 0.15 ± 0.1), and the PVN (59.8 ± 7.9 vs. 0.7 ± 0.7) had increases ( P < 0.05) in the average number of Fos-positive cells per field compared with controls, whereas the median preoptic nucleus did not. Double immunostaining for Fos and arginine vasopressin (AVP) or oxytocin (OT) indicated that AVP- but not OT-immunopositive neurons in SON and PVN respond to osmotic challenge. These results demonstrate that the SFO, OVLT, SON, and PVN are activated by osmotic challenge in fetal sheep at 130 dGA.
Acute hyperglycemia abolishes ischemic preconditioning in vivo
Authors: Kersten Judy R. , Schmeling Todd J. , Orth Karl G. , Pagel Paul S. , Warltier David C.
Published: December 2017

Ischemic preconditioning provides a powerful means to reduce myocardial infarct size in vivo and has been proposed to limit the extent of myocardial infarction in patients. In contrast, hyperglycemia correlates with increases in mortality after acute myocardial infarction. Thus we hypothesized that acute hyperglycemia alters the protection afforded by ischemic preconditioning, and this hypothesis was tested in acutely instrumented dogs subjected to a prolonged (60 min) coronary artery occlusion and 3 h of reperfusion. Ischemic preconditioning was elicited by four 5-min occlusion-reperfusion periods in the presence or absence of an intravenous infusion of 15% dextrose in water to produce acute hyperglycemia (plasma glucose concentration of 300 mg/dl). The dose-dependent effects of hyperglycemia on myocardial infarct size independent of preconditioning stimuli were further evaluated in dogs subjected to increases in plasma glucose concentrations to either 300 or 600 mg/dl. Infarct size (triphenyltetrazolium staining) was 24 ± 2% of the area at risk in control dogs and was significantly ( P < 0.05) decreased by ischemic preconditioning (8 ± 1%). Modest degrees of hyperglycemia (300 mg/dl) had no effect on infarct size (34 ± 4%) but abolished the protective effect of ischemic preconditioning (30 ± 5%). In contrast, profound hyperglycemia (600 mg/dl) increased infarct size (44 ± 6%). Hemodynamics and coronary collateral blood flow (radioactive microspheres) were similar between groups. Thus acute hyperglycemia adversely modulates myocardial injury in response to ischemia in vivo.
Regulation of KCa-channel activity by cyclic ADP-ribose and ADP-ribose in coronary arterial smooth muscle
Authors: Li Pin-Lan , Zou Ai-Ping , Campbell William B.
Published: December 2017

The enzymatic pathway responsible for the production and metabolism of cyclic ADP-ribose (cADP-R) in small bovine coronary arteries was characterized, and the role of cADP-R and ADP-ribose (ADP-R) in the regulation of the activity of large-conductance Ca2+-activated K+(KCa) channels was determined in vascular smooth muscle cells (SMC) prepared from these vessels. We found that cADP-R and ADP-R were produced when the coronary arterial homogenates were incubated with 1 mM β-NAD. The time course of the enzyme reactions showed that the maximal conversion rate (1.37 ± 0.03 nmol ⋅ min−1⋅ mg protein−1) of β-NAD to cADP-R was reached after 3 min of incubation. As incubation time was prolonged, the production of ADP-R was increased to a maximal rate of 3.66 ± 0.03 nmol ⋅ min−1⋅ mg protein−1, whereas cADP-R production decreased. Incubation of the homogenate with cADP-R produced a time-dependent increase in the synthesis of ADP-R. Comparison of coronary arterial microsomes with cytosols shows that the production of both cADP-R and ADP-R in microsomes was significantly greater. In excised inside-out membrane patches of single coronary SMC, the KCachannels were activated when β-NAD, the precursor for both cADP-R and ADP-R, was applied to the internal surface. This effect of β-NAD may be associated with the production of ADP-R, because the KCa-channel activity was increased by ADP-R in a concentration-dependent manner. The open-state probability of the KCachannels increased from a control level of 0.08 ± 0.03 to 0.17 ± 0.05 even at the lowest ADP-R concentration (0.1 μM) studied. However, cADP-R reduced the KCa-channel activity, and the threshold concentration of cADP-R that decreased the average channel activity of the KCachannels was 1 μM. These results provide evidence that cADP-R is produced and metabolized in the coronary arterial smooth muscle and that a cADP-R/ADP-R pathway participates in the control of the KCa-channel activity in vascular SMC.
Proinflammatory cytokines depress cardiac efficiency by a nitric oxide-dependent mechanism
Authors: Panas Donna , Khadour Fadi H. , Szabó Csaba , Schulz Richard
Published: December 2017

Proinflammatory cytokines (interleukin-1β, tumor necrosis factor-α, and interferon-γ; Cytomix) depress myocardial contractile work partially by stimulating expression of inducible nitric oxide (NO) synthase (iNOS). Because NO and peroxynitrite inhibit myocardial O2consumption (MV˙o2), we examined whether this mechanism contributes to reduced cardiac work. In control isolated working rat hearts, cardiac work was stable for 60 min, followed by a decline from 60 to 120 min, without change in MV˙o2. Cardiac efficiency (work/MV˙o2) was therefore reduced from 60 to 120 min. Cytomix shortened the onset (within 20–40 min) and enhanced the depression in cardiac work and efficiency and inhibited MV˙o2after 80 min. Mercaptoethylguanidine (MEG), an iNOS inhibitor and peroxynitrite scavenger, or the glucocorticoid dexamethasone (Dex) abolished the effects of Cytomix. iNOS expression was increased 10-fold by Cytomix and abolished by Dex but not MEG. That cytokine-induced depression in cardiac work precedes the reduction in MV˙o2suggests, at least in the early response, that NO and/or peroxynitrite may not impair heart function by inhibiting mitochondrial respiration but reduce the heart’s ability to utilize ATP for contractile work.
Signal transduction in activation of ischemically sensitive abdominal visceral afferents: role of PKC
Authors: Guo Zhi-Ling , Fu Liang-Wu , Symons J. David , Longhurst John C.
Published: December 2017

Abdominal ischemia reflexly activates the cardiovascular system by stimulating abdominal visceral afferent nerve endings. Whereas many ischemic metabolites responsible for activating these nerves have been identified (e.g., bradykinin), their precise mechanism of action is unclear. Protein kinase C (PKC) is an important part of the signal transduction process underlying the action of metabolites such as bradykinin and is a regulator of neuronal activity. Therefore, we hypothesized that PKC contributes to stimulation of ischemically sensitive abdominal visceral afferents. Single-unit activity was recorded from the right thoracic sympathetic chain of anesthetized cats. Exogenous activation of PKC using phorbol 12,13-dibutyrate (PDBu, 5 μg/kg ia) increased the impulse activity of ischemically sensitve C-fiber afferents from 0.04 ± 0.01 to 0.67 ± 0.23 impulses/s ( n = 11; P < 0.05). The influence of endogenous activation of PKC also was evaluated during 10 min of mesenteric ischemia. Inhibition of PKC using PKC-(19—36) (20 μg/kg iv) reduced ischemia-induced increases in afferent activity from 0.46 ± 0.11 to 0.19 ± 0.08 impulses/s ( n = 7, P < 0.05). Moreover, PKC-(19—36) (20 μg/kg iv) reduced the response of ischemically sensitive C fibers to bradykinin (0.5–1.0 μg/kg ia) from 1.18 ± 0.20 to 0.66 ± 0.14 impulses/s ( n = 13, P < 0.05). These results indicate that PKC contributes to activation of abdominal visceral afferents during ischemia and specifically to part of the bradykinin-induced activation of these afferents.
In vitro release of vascular endothelial growth factor during platelet aggregation
Authors: Maloney James P. , Silliman Christopher C. , Ambruso Daniel R. , Wang Jun , Tuder Rubin M. , Voelkel Norbert F.
Published: December 2017

Platelet aggregation is a cardinal feature of both vascular repair and vascular disease. During aggregation platelets release a variety of vasoactive substances; some of these promote angiogenesis, endothelial permeability, and endothelial growth, actions shared by vascular endothelial growth factor (VEGF). This study was undertaken to investigate the hypothesis that VEGF is released by aggregating platelets. We found that VEGF was secreted during the in vitro aggregation of platelet-rich plasma induced by thrombin, collagen, epinephrine, and ADP (range 23–518 pg VEGF/ml). Furthermore, serum VEGF levels were elevated compared with plasma (230 ± 63 vs. 38 ± 8 pg VEGF/ml), indicative of VEGF release during whole blood coagulation. Lysates of apheresed, leukocyte-poor platelet units contained significant amounts of VEGF (2.4 ± 0.8 pg VEGF/mg protein). VEGF message and protein were also present in a megakaryocytic cell line (Dami cell). These results suggest constitutive roles for platelet VEGF in the repair of intimal vessel injury and in the altered permeability and intimal proliferation seen at sites of platelet aggregation and thrombosis.
Depression of endothelial and smooth muscle cell oxygen consumption by endotoxin
Authors: Motterlini Roberto , Kerger Heinz , Green Colin J. , Winslow Robert M. , Intaglietta Marcos
Published: December 2017

An optical method based on the oxygen-dependent quenching of a phosphorescent probe (palladium-porphyrin) was used to investigate the effect of bacterial endotoxin [lipopolysaccharide (LPS)] on oxygen consumption (V˙o2) by vascular cells. Endothelial (EC) and smooth muscle (SMC) cells from pig aorta were suspended in culture medium in the presence of palladium-porphyrin and transferred to glass capillary tubes that were sealed to create a hypoxic environment. Measured [Formula: see text]changed as a function of time in a highly predictable fashion when cell suspensions were exposed to agents or treatment known to affect cellular metabolism. Both EC and SMC showed a significant decrease inV˙o2as cell density increased, and SMC V˙o2was significantly higher than EC (1.94 ± 0.09 vs. 1.0 ± 0.15 nmol ⋅ min−1⋅ 106cells−1). Exposure to LPS (1 μg/ml) caused a decrease inV˙o2of 46% and 15% for EC and SMC, respectively. Pretreatment of cells with N-acetyl-l-cysteine, a substrate for glutathione synthesis with antioxidant properties, restored V˙o2to normal values after exposure to LPS. These data suggest that endotoxin impairsV˙o2in cells derived from the vascular wall and indicate the importance of EC and SMC respiration in maintaining vascular homeostasis under conditions of sepsis.
Role of G1phase cyclins and cyclin-dependent kinases during cardiomyocyte hypertrophic growth in rats
Authors: Li Jian-Mei , Poolman Robert A. , Brooks Gavin
Published: December 2017

Cell cycle regulatory molecules are implicated in cardiomyocyte hypertrophy. We have investigated protein expression of cyclins A, D1–3, and E and cyclin-dependent kinases (CDKs) 2, 4, 5, and 6 in left ventricular (LV) tissues during the development of LV hypertrophy in rats following aortic constriction (AC). Compared with their expression in sham-operated controls (SH), expression of cyclins D2 and D3 and of CDK4 and CDK6 increased significantly from day 3 to day 21 after AC concomitant with increased LV mass. However, no significant difference was observed for CDK2 or CDK5. Cyclins A, D1, and E were undetectable. In vitro kinase activities of CDK4 and CDK6 increased ∼70% from day 7 to day 14 in AC myocytes compared with SH myocytes ( P< 0.03). Fluorescence-activated cell sorter analysis revealed a G0/G1to G2/M phase progression in AC myocyte nuclei (22.0 ± 1.1% in G2/M) by day 7 postoperation compared with progression in SH myocyte nuclei (14.0 ± 0.8% in G2/M; P < 0.01). Thus an upregulation of certain cell cycle regulators is associated with cardiomyocyte hypertrophy.
Role of AT1and AT2receptors in regulation of MAPKs and MKP-1 by ANG II in adult cardiac myocytes
Authors: Fischer Thomas A. , Singh Krishna , O’Hara Donald S. , Kaye David M. , Kelly Ralph A.
Published: December 2017

ANG II has been implicated in the hypertrophic response in ventricular myocytes by acting at the angiotensin type 1 (AT1) receptor. However, the role of the angiotensin type 2 (AT2) receptor in the adult heart is not as clearly understood. In adult rat ventricular myocytes (ARVM) and cardiac microvascular endothelial cells (CMEC), we examined the role of ANG II signaling, via AT1and AT2receptors, on the activation of the extracellular signal-regulated protein kinases (ERKs) and on the expression of the mitogen-activated protein kinase (MAPK) phosphatase MKP-1. ANG II caused no detectable increase in ERK activity or in c- fos mRNA abundance in ARVM but increased ERK activity within 5 min in CMEC and increased c- fos mRNA levels. However, in the presence of the selective phosphoprotein phosphatase (PP-2A/PP-1) inhibitor okadaic acid (OA), a sustained increase in ERK activity, as well as in c- junNH2-terminal protein kinase activity, in ARVM was observed. ANG II increased MKP-1 mRNA levels within 15 min in ARVM and CMEC. In contrast to the response in endothelial cells, however, ANG II activation of MKP-1 in ARVM was mediated by AT2-receptor activation. Thus there is constitutive as well as inducible suppression of ERKs and c- junNH2-terminal protein kinases by MKP and PP-2A/PP-1 in the adult cardiac myocyte phenotype.
Reflex vascular responses in the anesthetized dog to large rapid changes in carotid sinus pressure
Authors: Doe C. P. A. , Self D. A. , Drinkhill M. J. , McMahon N. , Myers D. S. , Hainsworth R.
Published: December 2017

This study examined reflex vascular responses to large rapid increases and decreases in carotid sinus pressure to determine whether delayed or inappropriate vascular responses might be obtained that, if they occurred in people, could lead to hypotension during exposure to rapidly alternating gravitational forces. In chloralose-anesthetized open-chest dogs, a perfusion circuit controlled carotid sinus and thoracic aortic pressures and blood flows to both the vascularly isolated abdominal circulation and a hindlimb (perfusion pressure changes denoted resistance). When carotid pressure was increased and decreased over the range of 60–180 mmHg, the resulting reflex vasodilatation occurred significantly more rapidly than the vasoconstriction ( P < 0.001). In the abdominal vascular bed, time constants for vasodilatation and vasoconstriction were 4.2 ± 0.5 and 7.5 ± 1.0 s, respectively. Decreases in carotid pressure in pulses of 10-s duration or less failed to elicit maximal vasoconstriction, whereas increases in carotid pressure lasting as little as 5 s did elicit maximal vasodilatation. “Square-wave” alternations in carotid pressure with periods of 10 s or less (5 s high, 5 s low) resulted in attenuation of the vasoconstriction, and at a 4-s period, both vascular beds remained almost maximally vasodilated throughout. The failure of vascular resistance to follow carotid pressure changes was not due to a failure of the response of sympathetic efferent activity, since the time constants for the reduction and increase in discharge were much shorter at 0.56 ± 0.13 and 0.43 ± 0.10 s, respectively. These results indicate that rapid changes in carotid pressure could result in inappropriate vasodilatation and hypotension and might, in some circumstances, such as in pilots flying high-performance aircraft, predispose to syncope.
31P NMR studies of creatine kinase flux in M-creatine kinase-deficient mouse heart
Authors: Van Dorsten Ferdi A. , Nederhoff Marcel G. J. , Nicolay Klaas , Van Echteld Cees J. A.
Published: December 2017

Hearts of wild-type and cytosolic muscle creatine kinase (M-CK)-knockout mice were perfused with Krebs-Henseleit buffer containing 10 mM glucose and 5 mM pyruvate and studied during pacing at 400 and 600 beats/min and during K+arrest. Phosphocreatine (PCr) and ATP concentrations in M-CK-deficient hearts were not significantly different from those in wild-type hearts. With the use of31P NMR saturation transfer, the flux mediated predominantly by mitochondrial creatine kinase (Mi-CK) was clearly detected in M-CK-deficient hearts. Mi-CK flux was 4.8 ± 0.6 and 4.5 ± 0.6 mM/s during pacing at 400 and 600 beats/min, respectively, and was 3.5 ± 0.4 mM/s during cardiac arrest. In control hearts total CK flux was 7.8 ± 1.1 and 6.6 ± 1.3 mM/s during pacing at 400 and 600 beats/min, respectively, and decreased to 3.8 ± 0.5 mM/s during arrest. It is suggested that the relative contribution of Mi-CK to the total NMR-measured CK flux in the wild-type heart is higher than that of the homodimeric M-CK isoform (MM-CK).
Amino-terminal proBNP in ovine plasma: evidence for enhanced secretion in response to cardiac overload
Authors: Pemberton C. J. , Yandle T. G. , Rademaker M. T. , Charles C. J. , Aitken G. D. , Espiner E. A.
Published: December 2017

We have recently identified a novel amino-terminal fragment of pro-brain natriuretic peptide (NT-proBNP) in the circulation of humans, the concentration of which increases progressively as the left ventricle fails. To clarify the origins of NT-proBNP in experimental animals, we have developed an RIA for NT-proBNP based on residues 52–71 of ovine proBNP-(1—103) and used it to study cardiac processing, secretion, and metabolism of BNP in sheep with cardiac overload induced by coronary artery ligation (CAL) or rapid left ventricular pacing (rLVP). The concentration of NT-proBNP in left atrial plasma extracts drawn from normal control sheep was threefold that of mature BNP. Size-exclusion and reverse-phase HPLC analyses of plasma extracts coupled to RIA revealed a single peak of immunoreactive (ir) NT-proBNP [∼8,000 relative molecular weight ( Mr)], quite distinct from a single peak of ir-mature BNP (∼3,000 Mr). In contrast, ovine cardiac tissue contained only a single immunoreactive peak of high-molecular-weight BNP (∼11,000 Mr), consistent in size with proBNP-(1—103). Sampling from the cardiac coronary sinus in normal control sheep ( n = 5) and sheep with CAL ( n = 5) revealed that the molar ratio of NT-proBNP to mature BNP was similar. There was a significant gradient of both mature and NT-proBNP across the heart in normal sheep, whereas after CAL the gradient was significant for mature BNP only. In both forms of cardiac overload (CAL and rLVP), left atrial plasma levels of NT-proBNP were significantly increased above normal levels, in contrast with mature BNP levels, which were raised only in the rLVP group of animals. Blockade of natriuretic peptide metabolism in sheep with heart failure (induced by rLVP) raised mature BNP levels threefold but did not affect levels of NT-proBNP. In conclusion, these studies show that NT-proBNP is formed from proBNP stores during secretion and, compared with mature BNP, accumulates in plasma because metabolism of NT-proBNP appears to differ from that of mature BNP. Although its function, if any, remains unclear, plasma NT-proBNP may prove to be a sensitive marker of cardiac overload and/or decompensation.
Dissociation between regional dysfunction and β-adrenergic receptor signaling in heart failure
Authors: Anzai Toshihisa , Lai N. Chin , Gao Meihua , Hammond H. Kirk
Published: December 2017

We have previously shown that left ventricular (LV) pacing-induced heart failure is associated with preserved wall thickening in the interventricular septum (IVS) compared with the posterolateral wall (PLW). The current study focuses on the relationship between regional myocardial function and altered β-adrenergic receptor (β-AR) signaling. We studied 15 pigs: 6 controls and 9 paced from the left ventricle (225 beats/min, 26 ± 3 days). Heart failure was documented by decreased LV fractional shortening ( P < 0.0001) and increased left atrial pressure ( P < 0.0001). In heart failure, despite marked differences in basal regional function (percent wall thickening: IVS, 33 ± 10% vs. PLW, 13 ± 7%; P = 0.0003), there were no differences between the two regions in β-AR responsiveness, measured by regional wall thickening in response to dobutamine infusion and any measurement of adrenergic signaling. Adenylyl cyclase activity, β-AR number, and β-AR/Gscoupling were markedly reduced in failing LV without regional differences. In animals with heart failure, LV G protein receptor kinase (GRK) isoform 2 content was unchanged and GRK5, the other major GRK isoform, was increased more than threefold (IVS, 0.51 ± 0.20 vs. 0.12 ± 0.12 arbitrary densitometric units, P = 0.01; PLW, 0.47 ± 0.15 vs. 0.13 ± 0.09 arbitrary densitometric units, P = 0.03), but again, there were no regional differences. These data indicate that systemic rather than regional factors govern LV adrenergic signaling and that regional adrenergic signaling abnormalities poorly predict wall thickening in the same regions.
Ecto-5′-nucleotidase is not required for ischemic preconditioning in rabbit myocardium in situ
Authors: Miki Takayuki , Miura Tetsuji , Bünger Rolf , Suzuki Katsuo , Sakamoto Jun , Shimamoto Kazuaki
Published: December 2017

This study tested the hypothesis that cardiac ecto-5′-nucleotidase (ecto-5′-NT) activity during ischemic preconditioning (PC) contributes to augmented tolerance against ischemia, thereby reducing infarct size in the rabbit heart in situ. The effects of α,β-methylene-adenosine diphosphate (AOPCP), a selective inhibitor of ecto-5′-NT, on cardiovascular responses to AMP were measured to establish in vivo activities of the enzyme and its inhibitor. Left atrial infusion of AOPCP (0.75 mg ⋅ kg−1⋅ min−1) raised AOPCP plasma levels to 138 μM; under these conditions negative chronotropic and inotropic effects of AMP were blocked, demonstrating essentially full inhibition of ecto-5′-NT in the heart in situ. This AOPCP-blocked heart in situ model was used to examine the proposed contribution of ecto-5′-NT in ischemic PC. Myocardial infarction caused by 30-min ischemia was followed by 3-h reperfusion. Infarct size (IS) was measured and expressed as a percentage of the size of the area at risk (%IS/AR). In untreated controls, %IS/AR was 38.1 ± 3.8%; PC (5-min ischemia, 5-min reperfusion) markedly reduced %IS/AR to 10.0 ± 2.0%. Essentially identical IS reductions by PC were observed in AOPCP-blocked animals (%IS/AR = 13.8 ± 2.2 and 13.3 ± 1.8% in rabbits receiving AOPCP at 0.75 and 1.50 mg ⋅ kg−1⋅ min−1, respectively); here plasma AOPCP levels were established before and during PC but not during the subsequent prolonged ischemia. As expected, AOPCP also did not affect %IS/AR in non-PC controls (%IS/AR = 35.5 ± 3.7%). In contrast but as predicted, adenosine-receptor blockade by 8-phenyltheophylline (10 mg/kg iv) substantially attenuated IS reduction by PC in both AOPCP-blocked and control hearts (%IS/AR = 25.2 ± 4.3 and 21.8 ± 2.2%, respectively; P < 0.05 vs. PC alone). The results demonstrate that cardiac ecto-5′-NT is not required for ischemic PC against infarction in the rabbit.
Angiotensin II-induced hypertrophy of adult rat cardiomyocytes is blocked by nitric oxide
Authors: Ritchie Rebecca H. , Schiebinger Rick J. , Lapointe Margot C. , Marsh James D.
Published: December 2017

The aim of the present study was to test the hypothesis that bradykinin-stimulated release of nitric oxide (NO) and/or prostacyclin from endothelium blocks myocyte hypertrophy in vitro. Angiotensin II increased [3H]phenylalanine incorporation by 21 ± 2% in myocytes cocultured with endothelial cells; this was abolished by bradykinin in the presence of endothelial cells. Bradykinin increased cytosolic concentrations of cGMP by 29 ± 4% in myocytes cocultured with endothelial cells. This was abolished by inhibition of NO synthase and by a cyclooxygenase inhibitor. Angiotensin II also increased [3H]phenylalanine incorporation by 28 ± 3% in myocytes cultured in the absence of endothelial cells. This effect of angiotensin II in monoculture was abolished by donors of NO but not by bradykinin. Neither the stable analog of prostacyclin (iloprost) nor the prostacyclin second messanger analog 8-bromo-cAMP (8-BrcAMP) blocked the effect of angiotensin II. Furthermore, 8-BrcAMP and iloprost individually increased [3H]phenylalanine incorporation. The antihypertrophic effects of bradykinin are critically dependent on endothelium-derived NO.
Downregulation of ventricular contractile function during early ischemia is flow but not pressure dependent
Authors: He Miao-Xiang , Downey H. Fred
Published: December 2017

The mechanism responsible for the abrupt fall in myocardial contractile function following coronary artery obstruction is unknown. The “vascular collapse theory” hypothesizes that the fall in coronary perfusion pressure after coronary artery obstruction is responsible for contractile failure during early ischemia. To test the role of vascular collapse in downregulating myocardial contractile force at the onset of ischemia, coronary flow of isolated rat hearts was abruptly decreased by 50, 70, 85, and 100% of baseline, and subsequent changes in coronary perfusion pressure and ventricular function were recorded at 0.5-s intervals. At 1.5 s after flow reductions ranging from 50 to 100%, decreases in contractile function did not differ, although perfusion pressure varied significantly from 45 ± 1 to 20 ± 2 mmHg. When function fell to 50% of baseline, perfusion pressures ranged from 35 ± 0.5 to 2.5 ± 1 mmHg for flow reductions ranging from 50 to 100%. Identical contractile function at widely differing coronary perfusion pressures is incompatible with the vascular collapse theory.
TNF-α-induced endothelium-independent vasodilation: a role for phospholipase A2-dependent ceramide signaling
Authors: Johns Douglas G. , Webb R. Clinton
Published: December 2017

Ceramide is a novel second messenger generated by hydrolysis of membrane sphingomyelin by a neutral sphingomyelinase (nSMase). Cytokines such as tumor necrosis factor-α (TNF-α) have been shown to increase intracellular ceramide through phospholipase A2(PLA2)-dependent activation of nSMase. TNF-α has been shown to cause endothelium-independent relaxation in isolated blood vessels. We have previously shown that exogenously applied sphingomyelinase and ceramide cause endothelium-independent vasodilation in rat thoracic aortas (D. G. Johns, H. Osborn, and R. C. Webb. Biochem. Biophys. Res. Commun. 237: 95–97, 1997). In the present study, we tested the hypothesis that ceramide mediates TNF-α-induced vasodilation. In phenylephrine-contracted rat thoracic aortic rings (no endothelium), TNF-α caused concentration-dependent relaxation in the presence of cyclooxygenase and lipoxygenase inhibitors. The phospholipase A2antagonist 7,7-dimethyl-(5 Z,8 Z)-eicosadienoic acid (DEDA; 50 μM) and the nonselective PLA2antagonist quinacrine (30 μM) inhibited TNF-α-induced relaxation. In cultured rat aortic vascular smooth muscle cells, TNF-α (10−7g/ml) increased intracellular ceramide 1.5-fold over basal level (0.08 nmol/mg protein), which was blocked by the PLA2antagonist DEDA (50 μM). We conclude that PLA2activation and increased ceramide generation play a role in mediating TNF-α-induced endothelium-independent vasodilation.
Non-NMDA and NMDA receptors transmit area postrema input to aortic baroreceptor neurons in NTS
Authors: Chen Chao-Yin , Bonham Ann C.
Published: December 2017

We sought to determine whether glutamate acting at both N-methyl-d-aspartate (NMDA) and non-NMDA receptors transmits area postrema (AP) excitatory inputs to nucleus tractus solitarii (NTS) neurons in the aortic baroreceptor or vagal afferent pathways in vivo. In α-chloralose-anesthetized rabbits, we recorded extracellular NTS neuronal responses to low-frequency aortic depressor nerve (ADN), vagus nerve, and AP stimulation and to iontophoresis of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and NMDA during control, iontophoresis of 2,3-dihdroxy-6-nitro-7-sulfamoylbenzo( f)quinoxaline (NBQX),dl-2-amino-5-phosphonovaleric acid (AP5), or both, and recovery conditions. In neurons receiving AP and ADN inputs, NBQX attenuated AP- and ADN-evoked responses by 46 ( P = 0.0206) and 49% ( P = 0.0042). AP5 attenuated AP- and ADN-evoked responses by 39 ( P = 0.0270) and 40% ( P = 0.0157). NBQX + AP5 attenuated AP- and ADN-evoked responses by 74 ( P = 0.0040) and 75% ( P = 0.0028). In neurons receiving AP and vagal inputs, AP transmission was attenuated by 58, 60, and 98%; vagal transmission was attenuated by 62, 35, and 83% during NBQX, AP5, and both antagonists, respectively. These data suggest that both non-NMDA and NMDA receptors transmit AP input to NTS neurons in aortic baroreceptor or vagal afferent pathways.