bluuebunny/crossref_metadata_2025 huggingface dataset:
Acute exercise can improve cardioprotection without increasing heat shock protein content
Authors: Taylor Ryan P. , Harris M. Brennan , Starnes Joseph W.
Published: December 2017

The aim of this study was to determine the effects of acute bouts of exercise on myocardial recovery after ischemia and heat shock protein expression. Adult female Sprague-Dawley rats were divided into five groups: 1) 1-day run (1DR; n = 6) and 2) 3-day run (3DR; n = 7), in which rats ran for 100 min at a speed of 20 m/min up a 6° grade for 1 or 3 consecutive days; 3) 1-day cold run (1CR), in which rats ran the same as 1DR but with wet fur at 8°C, which prevented an elevation of core temperature ( n = 8); 4) heat shock sedentary (HS), in which rats had their core temperatures raised to 42°C one time for 15 min ( n = 5); and 5) sedentary control ( n=15). Cardiac function was analyzed 24 h after the last treatment using an isolated, working heart model. Nonpaced hearts were initially perfused under normoxic conditions, then underwent 17 min of global, normothermic (37°C) ischemia, and, finally, were allowed to recover for 30 min under normoxic conditions. The concentration of the 72-kDa heat shock protein (HSP 72) was measured in each left ventricle. Compared with that in the sedentary group, recovery of cardiac output × systolic pressure (CO × SP) was enhanced ( P < 0.05) in all treatment groups when the postischemic value was covaried with the preischemic value. No differences in CO × SP were found ( P > 0.05) between the following groups: 1DR vs. 3DR, 1DR vs. HS, and 1DR vs. 1CR. Heat shock protein concentration was significantly greater ( P < 0.05) than that in the sedentary controls in HS, 1DR, and 3DR groups, but not for 1CR. The concentration of HSP 72 was not significantly correlated with postischemic CO × SP ( R2= 0.197, P > 0.05). We conclude that acute bouts of exercise can produce cardioprotective effects without an elevation of HSP 72.
Regional differences in effects of E-4031 within the sinoatrial node
Authors: Kodama I. , Boyett M. R. , Nikmaram M. R. , Yamamoto M. , Honjo H. , Niwa R.
Published: December 2017

Effects of block of the rapid delayed rectifier K+current ( I K,r) by E-4031 on the electrical activity of small ball-like tissue preparations from different regions of the rabbit sinoatrial node were measured. The effects of partial block of I K,r by 0.1 μM E-4031 varied in different regions of the node. In tissue from the center of the node spontaneous activity was generally abolished, whereas in tissue from the periphery spontaneous activity persisted, although the action potential was prolonged, the maximum diastolic potential was decreased, and the spontaneous activity slowed. After partial block of I K,r, the electrical activity of peripheral tissue was more like that of central tissue under normal conditions. One possible explanation of these findings is that the density of I K,r is greater in the periphery of the node; this would explain the greater resistance of peripheral tissue to I K,r block and help explain why, under normal conditions, the maximum diastolic potential is more negative, the action potential is shorter, and pacemaking is faster in the periphery.
TAFII250, Egr-1, and D-type cyclin expression in mice and neonatal rat cardiomyocytes treated with doxorubicin
Authors: Saadane Nacéra , Alpert Lesley , Chalifour Lorraine E.
Published: December 2017

Differential display identified that gene fragment HA220 homologous to the transcriptional activator factor II 250 (TAFII250) gene, or CCG1, was increased in hypertrophied rodent heart. To determine whether TAFII250 gene expression is modified after cardiac damage, we measured TAFII250 expression in vivo in mouse hearts after injection of the cardiotoxic agent doxorubicin (DXR) and in vitro in DXR-treated isolated rat neonatal cardiomyocytes. In vivo atrial natriuretic factor (ANF), β-myosin heavy chain (β-MHC), Egr-1, and TAFII250 expression increased with dose and time after a single DXR injection, but only ANF and β-MHC expression were increased after multiple injections. After DXR treatment of neonatal cardiomyocytes we found decreased ANF, α-MHC, Egr-1, and TAFII250 expression. Expression of the TAFII250-regulated genes, the D-type cyclins, was increased after a single injection in adult mice and was decreased in DXR-treated cardiomyocytes. Thus expression of Erg-1, TAFII250, and the D-type cyclins is modulated after cardiotoxic damage in adult and neonatal heart.
Mapping propagation of mechanical activation in the paced heart with MRI tagging
Authors: Wyman Bradley T. , Hunter William C. , Prinzen Frits W. , McVeigh Elliot R.
Published: December 2017

The temporal evolution of three-dimensional (3-D) strain maps derived from magnetic resonance imaging (MRI) tagging were used to noninvasively evaluate mechanical activation in the left ventricle (LV) while seven canine hearts were paced in situ from three different sites: the base of the LV free wall (LVb), the right ventricular apex (RVa), and the right atrium (RA). Strain maps plotted against time showed the evolution of shortening over the entire LV midwall and were used to generate mechanical activation maps showing the onset of circumferential shortening. RA pacing showed rapid synchronous shortening; LVb pacing showed a wave front of mechanical activation propagating slowly and steadily from the pacing site, whereas RVa pacing showed regions of rapid and slower propagation. The mechanical (M) activation times correlated linearly with the electrical (E) activation (M = 1.06E + 8.4 ms, R = 0.95). The time for 90% activation of the LV was 63.1 ± 24.3 ms for RA pacing, 130.2 ± 9.8 ms for LVb pacing, and 121.3 ± 17.9 ms for RVa pacing. The velocity of mechanical activation was calculated for LVb and RVa pacing and was similar to values reported for electrical conduction in myocardium. The propagation of mechanical activation for RVa pacing showed regional variations, whereas LVb pacing did not.
5-HT2B-receptor antagonist LY-272015 is antihypertensive in DOCA-salt-hypertensive rats
Authors: Watts Stephanie W. , Fink Gregory D.
Published: December 2017

We previously demonstrated a change in the receptors mediating 5-hydroxytryptamine (5-HT)-induced contraction in arteries of deoxycorticosterone acetate (DOCA)-salt-hypertensive rats. Specifically, contraction to 5-HT is mediated primarily by 5-HT2A receptors in arteries from normotensive sham rats and by both 5-HT2A and 5-HT2B receptors in arteries from hypertensive rats. We hypothesized that the 5-HT2B receptor may play a role in maintaining the high blood pressure of DOCA-salt-hypertensive rats, and herein we provide data connecting in vitro and in vivo findings. The endothelium-denuded isolated superior mesenteric artery of DOCA-salt rats displayed a marked increase in maximum contraction to the newly available 5-HT2B-receptor agonist BW-723C86 compared with that of arteries from sham rats, confirming that the 5-HT2B receptor plays a greater role in 5-HT-induced contraction in arteries from DOCA-salt rats. In chronically instrumented rats, the 5-HT2B-receptor antagonist LY-272015 (0.3, 1.0, and 3.0 mg/kg iv at 30-min intervals) was given cumulatively 1 time/wk during 4 wk of continued DOCA-salt treatment. LY-272015 did not reduce blood pressure of the sham-treated rats at any time or dose. However, LY-272015 (1.0 and 3.0 mg/kg) significantly reduced mean blood pressure in a subgroup of week 3 (−20 mmHg) and week 4 DOCA-salt (−40 mmHg) rats that had extremely high blood pressure (mean arterial blood pressure ∼200 mmHg). Blockade of 5-HT2Breceptors by in vivo administration of LY-272015 (3.0 mg/kg) was verified by observing reduced 5-HT-induced contraction in rat stomach fundus, the tissue from which the 5-HT2B receptor was originally cloned. These data support the novel hypothesis that 5-HT2B-receptor expression is induced during the development of DOCA-salt hypertension and contributes to the maintenance of severe blood pressure elevations.
Effects of hindlimb suspension on cytosolic Ca2+ and [3H]ryanodine binding in cardiac myocytes
Authors: Halet Guillaume , Viard Patricia , Morel Jean-Luc , Mironneau Jean , Mironneau Chantal
Published: December 2017

Effects of a 14-day hindlimb suspension were examined on [3H]ryanodine binding to rat ventricular microsomes and on cytosolic Ca2+ concentration ([Ca2+]i) and voltage-dependent Ca2+channels in isolated ventricular myocytes. In suspended rats, the amplitude of the twitch [Ca2+]itransient was increased without significant modifications of the basal [Ca2+]iand sarcoplasmic reticulum content. Because cell capacitance, L-type Ca2+-current density, and Ca2+-channel gating were not significantly modified after suspension, the increase in [Ca2+]iwas expected to reside in a change in ryanodine receptors. Scatchard analysis of [3H]ryanodine binding revealed that suspension enhanced binding by increasing the affinity of the receptors for [3H]ryanodine without affecting the maximal binding capacity. Both Ca2+-release channel activity and [3H]ryanodine binding are modulated by Ca2+. However, the Ca2+ sensitivity of [3H]ryanodine binding remained unchanged after suspension. Taken together, these results suggest that the increase in twitch [Ca2+]itransients after suspension may result from a change in the intrinsic properties of the ryanodine receptors but not from a change in the expression level of these receptors.
Altered kinetics of contraction of mouse atrial myocytes expressing ventricular myosin regulatory light chain
Authors: Buck Scott H. , Konyn Patrick J. , Palermo Joseph , Robbins Jeffrey , Moss Richard L.
Published: December 2017

To investigate the role of myosin regulatory light chain isoforms as a determinant of the kinetics of cardiac contraction, unloaded shortening velocity was determined by the slack-test method in skinned wild-type murine atrial cells and transgenic cells expressing ventricular regulatory light chain (MLC2v). Transgenic mice were generated using a 4.5-kb fragment of the murine α-myosin heavy chain promoter to drive high levels of MLC2v expression in the atrium. Velocity of unloaded shortening was determined at 15°C in maximally activating Ca2+solution (pCa 4.5) containing (in mmol/l) 7 EGTA, 1 free Mg2+, 4 MgATP, 14.5 creatine phosphate, and 20 imidazole (ionic strength 180 mmol/l, pH 7.0). Compared with the wild type ( n = 10), the unloaded shortening velocity of MLC2v-expressing transgenic murine atrial cells ( n = 10) was significantly greater (3.88 ± 1.19 vs. 2.51 ± 1.08 muscle lengths/s, P < 0.05). These results provide evidence that myosin light chain 2 regulates cross-bridge cycling rate. The faster rate of cycling in the presence of MLC2v suggests that the MLC2v isoform may contribute to the greater power-generating capabilities of the ventricle compared with the atrium.
Sympathovagal balance: how should we measure it?
Authors: Goldberger Jeffrey J.
Published: December 2017

There are complex interactions between the sympathetic and parasympathetic nervous system inputs to the sinus node. The concept of “sympathovagal balance” reflects the autonomic state resulting from the sympathetic and parasympathetic influences. Despite widespread usage of a variety of heart rate (HR) variability parameters as indexes of sympathovagal balance, no index has been validated as a measure of sympathovagal balance. This study evaluated the utility of HR, HR variability, and a new parameter termed the vagal-sympathetic effect (VSE) as indexes of sympathovagal balance. The ideal parameter had to satisfy the following criteria: 1) the index should vary similarly among subjects in response to different autonomic conditions; 2) the variability in the index among subjects exposed to the same autonomic conditions should be small; and 3) the response of the index to various autonomic conditions should reflect the underlying changes in physiological state and have a meaningful interpretation. Volunteers [8 men, 6 women; mean age 28.5 ± 4.8 (SD) yr] were evaluated for the effects of sympathetic and parasympathetic stimulation and blockade on HR and HR variability. VSE was defined as the ratio of the R-R interval to the intrinsic R-R interval. VSE and R-R interval consistently changed in the expected directions with parasympathetic and sympathetic stimulation and blockade. A general linearized model was used to evaluate the response of each parameter. VSE and R-R interval had r 2 values of 0.847 and 0.852, respectively. Natural logarithm of the low-frequency power had an r 2value of 0.781 with lower r 2 values for all the other HR variability parameters. The coefficient of variation was also lowest for each condition tested for the VSE and the R-R interval. VSE and R-R interval best satisfy the criteria for the ideal index of sympathovagal balance. Because it is impractical under most conditions to measure the VSE as the index of sympathovagal balance, the most suitable index is the R-R interval.
Effect of Mg2+on stress, myosin phosphorylation, and ATPase activity in detergent-skinned swine carotid media
Authors: Su Xiaoling , Pott Jan Willem R. , Moreland Robert S.
Published: December 2017

Smooth muscle contraction has a relatively high requirement for free magnesium (Mg2+). In this study we examined the effect of Mg2+concentration ([Mg2+]) on Ca2+-dependent stress development and stress maintenance, myosin ATPase activity, and myosin light chain (MLC) phosphorylation levels in Triton X-100 detergent-skinned fibers of the swine carotid media. Increasing [Mg2+] in a stepwise fashion from 0.1 to 6 mM 1) decreased the magnitude and Ca2+sensitivity of stress development but augmented the amount of stress maintained without proportional MLC phosphorylation, 2) produced a greater decrease in the Ca2+sensitivity of MLC phosphorylation than that of stress development, and 3) decreased myosin ATPase activity. These findings demonstrate that Mg2+differentially modulates the MLC phosphorylation-dependent development of stress and the MLC phosphorylation-independent maintenance of stress. We suggest that increases in [Mg2+] enhance stress maintenance by increasing [MgADP], thus increasing the number of cross bridges in a force-generating state, and by a direct effect on the pathway responsible for Ca2+-dependent, MLC phosphorylation-independent contractions.
Myocardial ischemia-reperfusion injury is exacerbated in absence of endothelial cell nitric oxide synthase
Authors: Jones Steven P. , Girod Wesley G. , Palazzo Anthony J. , Granger D. Neil , Grisham Matthew B. , Jourd’Heuil David , Huang Paul L. , Lefer David J.
Published: December 2017

Myocardial ischemia and reperfusion (MI/R) initiates a cascade of polymorphonuclear neutrophil (PMN)-mediated injury, the magnitude of which may be influenced by the bioavailability of nitric oxide (NO). We investigated the role of endothelial cell nitric oxide synthase (ecNOS) in MI/R injury by subjecting wild-type and ecNOS-deficient (−/−) mice to 20 min of coronary artery occlusion and 120 min of reperfusion. Myocardial infarct size represented 20.9 ± 2.9% of the ischemic zone in wild-type mice, whereas the ecNOS −/− mice had significantly ( P < 0.01) larger infarcts measuring 46.0 ± 3.8% of the ischemic zone. Because P-selectin is thought to be involved with the pathogenesis of neutrophil-mediated I/R injury, we assessed the effects of MI/R on P-selectin expression in the myocardium of wild-type and ecNOS −/− mice. P-selectin expression measured with a radiolabeled monoclonal antibody (MAb) technique after MI/R in wild-type mice was 0.037 ± 0.009 μg MAb/g tissue, whereas ecNOS −/− coronary vasculature was characterized by significantly ( P < 0.05) higher P-selectin expression (0.080 ± 0.013 μg MAb/g tissue). Histological examination of the postischemic myocardium revealed significantly ( P < 0.01) more neutrophils in the ecNOS −/− (29.5 ± 2.5 PMN/field) compared with wild-type (5.0 ± 0.9 PMN/field) mice. A similar trend in infarct size and neutrophil accumulation was observed when wild-type and ecNOS −/− mice were subjected to 30 min of ischemia and 120 min of reperfusion. These novel in vivo findings demonstrate a cardioprotective role for ecNOS-derived NO in the ischemic-reperfused mouse heart.
Dynamics of tissue oxygenation in isolated rabbit heart as measured with near-infrared spectroscopy
Authors: de Groot Bas , Zuurbier Coert J. , van Beek Johannes H. G. M.
Published: December 2017

We investigated the role of myoglobin (Mb) in supplying O2to mitochondria during transitions in cardiac workload. Isovolumic rabbit hearts ( n = 7) were perfused retrogradely with hemoglobin-free Tyrode solution at 37°C. Coronary venous O2tension was measured polarographically, and tissue oxygenation was measured with two-wavelength near-infrared spectroscopy (NIRS), both at a time resolution of ∼2 s. During transitions to anoxia, 68 ± 2% (SE) of the NIRS signal was due to Mb and the rest to cytochrome oxidase. For heart rate steps from 120 to 190 or 220 beats/min, the NIRS signal decreased significantly by 6.9 ± 1.3 or 11.1 ± 2.1% of the full scale, respectively, with response times of 11.0 ± 0.8 or 9.1 ± 0.5 s, respectively. The response time of end-capillary O2concentration ([O2]), estimated from the venous [O2], was 8.6 ± 0.8 s for 190 beats/min ( P< 0.05 vs. NIRS time) or 8.5 ± 0.9 s for 220 beats/min ( P > 0.05). The mean response times of mitochondrial O2consumption (V˙o2) were 3.7 ± 0.7 and 3.6 ± 0.6 s, respectively. The deoxygenation of oxymyoglobin (MbO2) accounted for only 12–13% of the total decrease in tissue O2, with the rest being physically dissolved O2. During 11% reductions in perfusion flow at 220 beats/min, Mb was 1.5 ± 0.4% deoxygenated ( P < 0.05), despite the high venous [Formula: see text] of 377 ± 17 mmHg, indicating metabolism-perfusion mismatch. We conclude that the contribution of MbO2to the increase of V˙o2during heart rate steps in saline-perfused hearts was small and slow compared with that of physically dissolved O2.
Ischemia-reperfusion induced microvascular responses in LDL-receptor −/− mice
Authors: Mori Naoharu , Horie Yoshinori , Gerritsen Mary E. , Granger D. Neil
Published: December 2017

The objective of this study was to determine whether the microvascular responses to ischemia and reperfusion (I/R) are altered in an animal model of atherosclerosis, the low-density lipoprotein-receptor knockout (LDLr −/−) mouse. Intravital video microscopy was used to monitor venular wall shear rate, leukocytes rolling velocity, the number of rolling, adherent and emigrated leukocytes, and albumin leakage in cremasteric postcapillary venules of wild-type (B6129) and LDLr −/− mice exposed to 60 min of ischemia and 60 min of reperfusion. The postcapillary venules of LDLr −/− mice exhibited two- to threefold larger increments in the number of adherent leukocytes and a more profound albumin leakage response to I/R than venules in wild-type mice. The exaggerated inflammatory responses noted in LDLr −/− mice placed on a normal diet were not exacerbated by a high-cholesterol diet. Treatment of LDLr −/− mice with either a platelet-activating factor (PAF) receptor antagonist (WEB-2086) or a monoclonal antibody (YN-1) against the endothelial cell adhesion molecule, intercellular adhesion molecule 1 (ICAM-1), markedly attenuated the I/R-induced leukocyte adherence and albumin leakage. These findings indicate that atherogenic mice are more vulnerable to the deleterious microvascular effects of I/R and that PAF-mediated, ICAM-1-dependent leukocyte adhesion contributes to this exaggerated response to I/R.
Cellular and molecular remodeling in a heart failure model treated with the β-blocker carteolol
Authors: Gwathmey Judith K. , Kim Catherine S. , Hajjar Roger J. , Khan Farid , DiSalvo Thomas G. , Matsumori Akira , Bristow Michael R.
Published: December 2017

Broad-breasted white turkey poults fed furazolidone developed dilated cardiomyopathy (DCM) characterized by ventricular dilatation, decreased ejection fraction, β1-receptor density, sarcoplasmic reticulum (SR) Ca2+-ATPase, myofibrillar ATPase activity, and reduced metabolism markers. We investigated the effects of carteolol, a β-adrenergic blocking agent, by administrating two different dosages (0.01 and 10.0 mg/kg) twice a day for 4 wk to control and DCM turkey poults. At completion of the study there was 59% mortality in the nontreated DCM group, 55% mortality in the group treated with the low dose of carteolol, and 22% mortality in the group treated with the high dose of carteolol. Both treated groups showed a significant decrease in left ventricle size and significant restoration of ejection fraction and left ventricular peak systolic pressure. Carteolol treatment increased β-adrenergic receptor density, and the high carteolol dose restored SR Ca2+-ATPase and myofibrillar ATPase activities, along with creatine kinase, lactate dehydrogenase, aspartate transaminase, and ATP synthase activities, to normal. These results show that β-blockade with carteolol improves survival, reverses contractile abnormalities, and induces cellular remodeling in this model of heart failure.
Changes in coronary endothelial cell Ca2+concentration during shear stress- and agonist-induced vasodilation
Authors: Muller Judy M. , Davis Michael J. , Kuo Lih , Chilian William M.
Published: December 2017

Increases in intraluminal shear stress are thought to cause vasodilation of coronary arterioles by activation of Ca2+-dependent endothelial nitric oxide synthase followed by release of nitric oxide. We tested the hypothesis that endothelium-dependent vasodilation of isolated coronary arterioles to shear stress and agonists is necessarily preceded by an increase in endothelial cell Ca2+concentration ([Ca2+]i). After selective loading of endothelium in isolated rabbit coronary arterioles with fura 2, simultaneous changes in diameter and [Ca2+]iwere recorded. Vasodilations recorded in response to ACh, substance P, or shear stress were accompanied by significant increases in endothelial cell [Ca2+]i. Vasodilations to shear stress were accompanied by smaller changes in endothelial cell [Ca2+]ithan equivalent dilations evoked by substance P or ACh. To test the role for Ca2+as an activator of endothelial nitric oxide synthase, the endothelium was treated with the Ca2+chelator 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid. 1,2-Bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid eliminated significant changes in endothelial cell [Ca2+]iand inhibited dilations to ACh and substance P but did not significantly affect shear stress-induced vasodilation. The data indicate that endothelium-dependent vasodilation of coronary arterioles in response to agonists and shear stress is mediated in part through a rise in endothelial cell [Ca2+]ibut that a substantial component of the shear stress-induced response occurs through a Ca2+-insensitive pathway.
An α-cardiac myosin heavy chain gene mutation impairs contraction and relaxation function of cardiac myocytes
Authors: Kim Song-Jung , Iizuka Kenji , Kelly Ralph A. , Geng Yong-Jian , Bishop Sanford P. , Yang Guiping , Kudej Amelia , McConnell Bradley K. , Seidman Christine E. , Seidman Jonathan G. , Vatner Stephen F.
Published: December 2017

Left Ventricular (LV) myocytes were isolated from 15-wk-old male mice bearing the Arg403→ Gln α-cardiac myosin heavy chain missense mutation (α-MHC403/+), a model of familial hypertrophic cardiomyopathy. LV myocytes were classified morphologically: type I, rod shaped with parallel myofibrils; type II, irregularly shaped, shorter and wider than wild-type (WT) control cells, with parallel myofibrils; and type III, irregularly shaped with disoriented myofibrils. Compared with WT myocytes, α-MHC403/+myocytes had fewer type I cells (WT = 74 ± 3%, α-MHC403/+= 41 ± 4%, P < 0.01) and more type III cells (WT= 12 ± 3%, α-MHC403/+= 49 ± 7%, P < 0.01). In situ histology also demonstrated marked myofibrillar disarray in the α-MHC403/+hearts. With the use of video edge detection, myocytes were paced at 1 Hz (37°C) to determine the effects of the mutation on myocyte function. End-diastolic length was reduced in mutant myocytes, but fractional shortening (% contraction) and sarcomere length were not. Velocity of contraction (−d L/d tmax) was depressed in mutant cells, but more in type II and III cells (−31%) than in type I cells (−18%). Velocity of relaxation (+d L/d t) was also depressed more in type II and III cells (−38%) than in type I cells (−16%). Using fura 2 dye with intracellular Ca2+transients, we demonstrated that in α-MHC403/+myocytes, the amplitude of the Ca2+signal during contraction was unchanged but that the time required for decay of the signal to decrease 70% from its maximum was delayed significantly (WT = 159 ± 8 ms; α-MHC403/+= 217 ± 14 ms, P < 0.01). Sarco(endo)plasmic reticulum Ca2+-ATPase mRNA levels in α-MHC403/+and WT mice were similar. These data indicate that the altered cardiac dysfunction of α-MHC403/+myocytes is directly due to defective myocyte function rather than to secondary changes in global cardiac function and/or loading conditions.
Activation of GABAA but not GABAB receptors in the NTSblocked bradycardia of chemoreflex in awake rats
Authors: Callera João Carlos , Bonagamba Leni G. H. , Nosjean Anne , Laguzzi Raul , Machado Benedito H.
Published: December 2017

In the present study we analyzed effects of bilateral microinjections of muscimol (a GABAA agonist) and baclofen (a GABAB agonist) into the nucleus tractus solitarius (NTS) on bradycardic and pressor responses to chemoreflex activation (potassium cyanide, 40 μg/rat iv) in awake rats. Bilateral microinjections of muscimol (25 and 50 pmol/50 nl) into the NTS increased baseline mean arterial pressure (MAP): 119 ± 8 vs. 107 ± 2 mmHg ( n = 6) and 121 ± 8 vs. 103 ± 3 mmHg ( n= 6), respectively. Muscimol at 25 pmol/50 nl reduced the bradycardic response to chemoreflex activation 5 min after microinjection; with 50 pmol/50 nl the bradycardic response to chemoreflex activation was reduced 5, 15, 30, and 60 min after microinjection. Neither muscimol dose produced an effect on the pressor response of the chemoreflex. Effects of muscimol (50 pmol/50 nl) on basal MAP and on the bradycardic response of the chemoreflex were prevented by prior microinjection of bicuculline (a GABAA antagonist, 40 pmol/50 nl) into the NTS. Bilateral microinjections of baclofen (12.5 and 25 pmol/50 nl) into the NTS produced an increase in baseline MAP [137 ± 9 vs. 108 ± 4 ( n= 7) and 145 ± 5 vs. 105 ± 2 mmHg ( n = 7), respectively], no changes in basal heart rate, and no effects on the bradycardic response; 25 pmol/50 nl only attenuated the pressor response to chemoreflex activation. The data show that activation of GABAA receptors in the NTS produces a significant reduction in the bradycardic response, whereas activation of GABAB receptors produces a significant reduction in the pressor response of the chemoreflex. We conclude that 1) GABAA but not GABAB plays an inhibitory role in neurons of the lateral commissural NTS involved in the parasympathetic component of the chemoreflex and 2) attenuation of the pressor response of the chemoreflex by activation of GABAB receptors may be due to inhibition of sympathoexcitatory neurons in the NTS or may be secondary to the large increase in baseline MAP produced by baclofen.
Regional ischemia increases sensitivity of left ventricular relaxation to volume in pigs
Authors: Solomon Steven B. , Glantz Stanton A.
Published: December 2017

Regional ischemia impairs early diastolic filling due, in part, to changes in left ventricular relaxation. This study uses open-chest pigs instrumented with high-fidelity pressure transducers to investigate the effect of regional ischemia on the active component of relaxation independent of the passive effects of filling and the effect of left ventricular filling and stretch on the rate, duration, and extent of relaxation. During regional ischemia, active relaxation was impaired in the nonfilling ventricle, with a slower rate of relaxation. Stretching the myocardium as the ventricle fills slows the rate of relaxation more during regional ischemia than during normal perfusion, reflecting an increased sensitivity to stretch due to filling and an increased dependence of relaxation on volume. The duration of relaxation depends on the effect of regional ischemia on the end-diastolic pressure-volume relation. Stronger baseline contractile function results in an upward shift in the end-diastolic pressure-volume relation during regional ischemia and no net effect on the duration of relaxation. If this curve is shifted upward, the duration of relaxation shortens. All these effects combine to reduce the atrioventricular pressure gradient and left ventricular filling during regional ischemia.
Species-dependent hemodynamic effects of adenosine A3-receptor agonists IB-MECA and Cl-IB-MECA
Authors: Lasley Robert D. , Narayan Prakash , Jahania M. Salik , Partin Elizabeth L. , Kraft Kathleen R. , Mentzer Robert M.
Published: December 2017

The purpose of this study was to compare the hemodynamic effects of the adenosine A3-receptor agonists N 6-(3-iodobenzyl)-9-[5-(methylcarbamoyl)-β-d-ribofuranosyl]adenine (IB-MECA) and 2-chloro- N 6-(3-iodobenzyl)-9-[5-(methylcarbamoyl)-β-d-ribofuranosyl]adenine (Cl-IB-MECA) in isolated rat and rabbit hearts and in the intact, open-chest pig. Isolated hearts perfused with Krebs-Henseleit buffer at a constant pressure (70 mmHg) were treated with 50 nM of either IB-MECA or Cl-IB-MECA. Neither IB-MECA nor Cl-IB-MECA altered ventricular function or heart rate in the isolated rat and rabbit hearts, and neither agent altered coronary flow in the rabbit. However, 2 min of IB-MECA treatment in the isolated rat heart increased coronary flow by 25%, an effect that did not exhibit tachyphylaxis. The IB-MECA-induced coronary dilation was only partially attenuated by the adenosine A3-receptor antagonist MRS-1191 (50 nM). IB-MECA-induced coronary dilation was completely blocked by the adenosine A2a-receptor antagonist 7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (Sch-58261, 50 nM). Cl-IB-MECA (50 nM) did not increase coronary flow in the rat, but 100 nM did increase flow by 18%. In pentobarbital sodium-anesthetized pigs IB-MECA (5 μg/kg iv) decreased systemic blood pressure and increased pulmonary artery pressure, effects that did exhibit tachyphylaxis. These results illustrate that adenosine A3-receptor agonists produce species-dependent effects, which in the rat heart appear to be caused by adenosine A2a-receptor activation.
Hemodynamic model for analysis of Doppler ultrasound indexes of umbilical blood flow
Authors: Kleiner-Assaf Ayala , Jaffa Ariel J. , Elad David
Published: December 2017

A hemodynamic model for pulsatile fluid flow in a pressurized thin-walled elastic tube was applied for the computation of volumetric blood flow and velocity profiles for a given set of system parameters at any selected location along the umbilical artery. The velocity profiles over one heart cycle provide the fetal blood flow velocity waveforms (FVW) from which the usual Doppler indexes (DI) can be derived. The model was used for a comprehensive investigation of the correlation between DI and system parameters that reflect the anatomy and physiology of umbilical blood flow. The simulations showed that the radial location of the Doppler measurement is insignificant for the calculated DI, whereas the axial site is important. The analysis showed that decreasing the diameter or increasing the length of the umbilical artery reduces fetal mean blood flow rate and increases the DI. Increasing blood viscosity tends to induce similar patterns, whereas decreasing arterial compliance or increasing blood density decreases the DI with little effect on blood flow rate. Fetal heart rate has a minor effect on both DI and fetal blood flow rate. This study provides insight into the dependence of DI on the anatomic and physiological characteristics of umbilical blood flow.
Alteration of microtubule polymerization modulates arteriolar vasomotor tone
Authors: Platts Steven H. , Falcone Jeff C. , Holton William T. , Hill Michael A. , Meininger Gerald A.
Published: December 2017

Microtubules are important cytoskeletal elements that have been shown to play a major role in many cellular processes because of their mechanical properties and/or their participation in various cell signaling pathways. We tested the hypothesis that depolymerization of microtubules would alter vascular smooth muscle (VSM) tone and hence contractile function. In our studies, isolated cremaster arterioles exhibited significant vasoconstriction that developed over a 20- to 40-min period when they were treated with microtubule depolymerizing drugs colchicine (10 μM), nocodazole (10 μM), or demecolcine (10 μM). Immunofluorescent labeling of microtubules in cultured rat VSM revealed that both colchicine and nocodazole caused microtubule depolymerization over a similar time course. The vasoconstriction was maintained over a wide range of intraluminal pressures (30–170 cmH2O). The increased tone was not affected by endothelial denudation, suggesting that it was due to an effect on VSM. Microtubule depolymerization with demecolcine or colchicine had no effect on VSM intracellular Ca2+concentration ([Ca2+]i). These data indicate that microtubules significantly interact with processes leading to the expression of vasomotor tone. The mechanism responsible for the effect of microtubules on vasomotor tone appears to be independent of both the endothelium and an increase in VSM [Ca2+]i.
Bradykinin prevents postischemic leukocyte adhesion and emigration and attenuates microvascular barrier disruption
Authors: Shigematsu Sakuji , Ishida Shuji , Gute Dean C. , Korthuis Ronald J.
Published: December 2017

Although a number of recent reports indicate that bradykinin attenuates ischemia- reperfusion (I/R)-induced tissue injury, the mechanisms underlying its protective actions are not fully understood. However, because bradykinin induces endothelial nitric oxide (NO) production and NO donors have been shown to attenuate postischemic leukocyte adhesion, endothelial barrier disruption, and tissue injury, we hypothesized that bradykinin may act to reduce I/R-induced tissue injury by preventing leukocyte recruitment and preserving microvascular barrier function. To address this postulate, we used intravital videomicroscopic approaches to quantify leukocyte-endothelial cell interactions and microvascular barrier function in single postcapillary venules in the rat mesentery. Reperfusion after 20 min of ischemia significantly decreased wall shear rate and leukocyte rolling velocity, increased the number of rolling, adherent, and emigrated leukocytes, and disrupted the microvascular barrier as evidenced by enhanced venular albumin leakage. Superfusion of the mesentery with bradykinin (10 nM) during I/R significantly reduced these deleterious effects of I/R. Although these inhibitory effects of bradykinin were not affected by cyclooxygenase blockade with indomethacin (10 μM), coadministration with NO synthase ( Nω-nitro-l-arginine methyl ester, 10 μM) or bradykinin B2-receptor (HOE-140, 1 μM) antagonists abolished the protective actions of bradykinin. Plasma NO concentration was measured in the mesenteric vein and was significantly decreased after I/R, an effect that was prevented by bradykinin treatment. These results indicate that bradykinin attenuates I/R-induced leukocyte recruitment and microvascular dysfunction by a mechanism that involves bradykinin B2-receptor-dependent NO production.
Contraction-relaxation coupling: determination of the onset of diastole
Authors: Solomon Steven B. , Nikolic Srdjan D. , Frater Robert W. M. , Yellin Edward L.
Published: December 2017

Left ventricular relaxation is dependent on afterload conditions during systole. An abrupt increase in afterload while the ventricle is actively contracting prolongs the duration of systole. An increase in afterload during ventricular relaxation shortens the duration of systole. Therefore, we hypothesized that the point during systole when an abrupt increase in afterload had no effect on the duration of systole represented the onset of ventricular relaxation. To determine when this point occurs, we performed aortic occlusions progressively throughout the duration of systole in six dogs. We determined the change in systolic time ( t sys) after an intervention normalized to t sys of a control beat ( t sys,i/ t sys,c) as a function of systolic occlusion time as a percentage of total systolic time ( t occ/ t sys,c), where t sys is the duration from time of left ventricular end-diastolic pressure to the time of minimum first derivative of left ventricular pressure. Our results show the onset of left ventricular relaxation during normal ejection occurs at 34 ± 3% of systolic time and ∼16% after the onset of ejection. Thus the beginning of relaxation occurs soon after the beginning of ejection, suggesting that relaxation is modulated by variable loading conditions during ejection, significantly before what has been conventionally been assumed to be the beginning of ventricular relaxation.
Impairment of EDR by a long-term PDGF treatment in organ-cultured rabbit mesenteric artery
Authors: Yamawaki Hideyuki , Sato Koichi , Hori Masatoshi , Ozaki Hiroshi , Nakamura Shin-Ichiro , Nakayama Hiroyuki , Doi Kunio , Karaki Hideaki
Published: December 2017

Platelet-derived growth factor (PDGF) has been shown to act chronically on blood vessels to regulate not only proliferation but also vascular tone. These effects may be at least partly due to the chronic effect of PDGF on vascular endothelium. To evaluate this possibility, we examined the effects of PDGF on the endothelium-dependent relaxation (EDR) and total RNA for endothelial nitric oxide (NO) synthase (eNOS) using an organ culture system. In rabbit mesenteric arteries cultured in a serum-free medium for 1 wk, amplitude of the substance P-induced EDR did not change, whereas dependency of the EDR on NO (∼60.0% vs. 18.9%) and the total amounts of recoverable eNOS mRNA estimated by RT-PCR were increased compared with those in freshly isolated arteries. Culture with PDGF for 1 wk decreased the relaxant effect of substance P and ionomycin ( P < 0.01 compared with the arteries without PDGF), NO production estimated by bioassay ( P < 0.01), and eNOS mRNA level, whereas the sodium nitroprusside-induced relaxation did not change. These results suggest that PDGF has a chronic effect on vascular endothelium to decrease eNOS mRNA and NO production and to impair NO-dependent EDR.
α-Adrenergic vasoconstriction in active skeletal muscles during dynamic exercise
Authors: Buckwalter John B. , Clifford Philip S.
Published: December 2017

Sympathetic vasoconstriction in working muscles during dynamic exercise has been demonstrated by intra-arterial administration of α1-adrenergic antagonists. The purpose of this study was to examine the existence of α1- and α2-adrenergic receptor-mediated vasoconstriction in active skeletal muscles during exercise. Six mongrel dogs were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs, and a catheter was inserted in one femoral artery. All dogs ran on a motorized treadmill at three exercise intensities (3 miles/h, 6 miles/h, and 6 miles/h at 10% grade) on separate days. After 5 min of exercise, a selective α1- (prazosin) or a selective α2-adrenergic antagonist (rauwolscine) was infused as a bolus into the femoral arterial catheter (only one drug per day). The doses of the antagonists were adjusted to maintain the same effective concentration at each exercise intensity. At the mild, moderate, and heavy workloads prazosin infusion produced immediate increases in iliac conductance of 65 ± 9, 35 ± 6, and 18 ± 4% (means ± SE), respectively, and increases in blood flow of 290 ± 24, 216 ± 23, and 172 ± 18 ml/min, respectively. Rauwolscine infusion produced increases in conductance of 52 ± 5%, 36 ± 5%, and 26 ± 3%, respectively, and blood flow increases of 250 ± 34, 244 ± 39, and 259 ± 35 ml/min at the three workloads. Systemic blood pressure and blood flow in the contralateral iliac artery were unaffected by any of the antagonist infusions. These results demonstrate that there is ongoing α1- and α2-adrenergic receptor-mediated vasoconstriction in exercising skeletal muscles even at heavy workloads and that the magnitude of vasoconstriction decreases as exercise intensity increases.
Oxygen delivery does not limit cardiac performance during high work states
Authors: Zhang Jianyi , Murakami Yo , Zhang Yi , Cho Yong K , Ye Yun , Gong Guangrong , Bache Robert J. , Uğurbil Kâmil , From Arthur H. L.
Published: December 2017

This study tested the hypothesis that the loss of myocardial high-energy phosphates (HEP), which occurs during high cardiac work states [J. Zhang, D. J. Duncker, Y. Xu, Y. Zhang, G. Path, H. Merkle, K. Hendrich, A. H. L. From, R. Bache, and K. Uğurbil. Am. J. Physiol. 268: ( Heart Circ. Physiol. 37): H1891–H1905, 1995], is not the result of insufficient intracellular O2 availability. To evaluate the state of myocardial oxygenation, the proximal histidine signal of deoxymyoglobin (Mb-δ) was determined with1H nuclear magnetic resonance spectroscopy (MRS), whereas HEP were examined with31P MRS. Normal dogs ( n = 11) were studied under basal conditions and during combined infusion of dobutamine and dopamine (20 μg ⋅ kg−1 ⋅ min−1iv each), which increased rate-pressure products to >50,000 mmHg ⋅ beats ⋅ min−1. Creatine phosphate (CP) was expressed as CP/ATP, and myocardial myoglobin desaturation was normalized to the Mb-δ resonance present during total coronary artery occlusion. This Mb-δ resonance appeared at 71 parts per million downfield from the water resonance. CP/ATP decreased from 2.22 ± 0.12 during the basal state to 1.83 ± 0.09 during the high work state ( P < 0.01), whereas ΔPi/CP increased from 0 to 0.21 ± 0.04 ( P < 0.01). Despite these HEP changes, Mb-δ remained undetectable. In contrast, when a coronary stenosis was applied to produce a similar decrease in CP/ATP, Mb-δ reached 0.38 ± 0.10 of the value present during total coronary occlusion. These data demonstrate that Mb-δ is readily detected in vivo during limitation of coronary blood flow sufficient to cause a decrease of myocardial CP/ATP. However, similar HEP changes that occur at high work states in the absence of coronary occlusion are not associated with a detectable Mb-δ resonance. The findings support the hypothesis that the myocardial HEP changes observed at high work states are not due to inadequate O2 availability to the mitochondria and emphasize the limitations of interpreting HEP alterations in the absence of knowing the level of myocyte oxygenation.
Inactivation gating determines nicotine blockade of human HERG channels
Authors: Wang Hui-Zhen , Shi Hong , Liao Shu-Jie , Wang Zhiguo
Published: December 2017

We have previously found that nicotine blocked multiple K+ currents, including the rapid component of delayed rectifier K+ currents ( I Kr), by interacting directly with the channels. To shed some light on the mechanisms of interaction between nicotine and channels, we performed detailed analysis on the human ether-à-go-go-related gene (HERG) channels, which are believed to be equivalent to the native I Kr when expressed in Xenopus oocytes. Nicotine suppressed the HERG channels in a concentration-dependent manner with greater potency with voltage protocols, which favor channel inactivation. Nicotine caused dramatic shifts of the voltage-dependent inactivation curve to more negative potentials and accelerated the inactivation process. Conversely, maneuvers that weakened the channel inactivation gating considerably relieved the blockade. Elevating the extracellular K+ concentration from 5 to 20 mM increased the nicotine concentration (by ∼100-fold) needed to achieve the same degree of inhibition. Moreover, nicotine lost its ability to block the HERG channels when a single mutation was introduced to a residue located after transmembrane domain 6 (S631A) to remove the rapid channel inactivation. Our data suggest that the inactivation gating determines nicotine blockade of the HERG channels.
Vascular smooth muscle cell growth arrest on blockade of thrombospondin-1 requires p21Cip1/WAF1
Authors: Chen Donghui , Guo Kun , Yang Jihong , Frazier William A. , Isner Jeffrey M. , Andrés Vicente
Published: December 2017

Abnormal proliferation of vascular smooth muscle cells (VSMCs) is thought to play an important role in the pathogenesis of atherosclerosis and restenosis. Previous studies have implicated the extracellular matrix protein thrombospondin-1 (TSP1) in mitogen-dependent proliferation of VSMCs. In this study, we investigated the molecular mechanisms involved in TSP1-mediated regulation of VSMC growth. Neutralizing A4.1 anti-TSP1 antibody inhibited the activity of the G1/S cyclin-dependent kinase 2 (cdk2) and blocked the induction of S-phase entry, which normally occurs in serum-stimulated VSMCs. This growth-inhibitory effect was associated with a marked induction of p21Cip1/WAF1(p21) expression in A4.1-treated VSMCs. Moreover, addition of A4.1 antibody to VSMCs markedly increased the level of p21 bound to cdk2. Thus growth arrest on antibody blockade of TSP1 may be mediated by the cdk inhibitory protein p21. Consistent with this notion, anti-TSP1 antibody inhibited [3H]-thymidine incorporation in wild-type but not in p21-deficient mouse embryonic fibroblasts (MEFs). Together, these data suggest that p21 plays an important role in TSP1-mediated control of cellular proliferation.
Quantification of murine endothelial cell adhesion molecules in solid tumors
Authors: Langley Robert R. , Russell Janice , Eppihimer Michael J. , Alexander Steven J. , Gerritsen Mary , Specian Robert D. , Granger D. Neil
Published: December 2017

Coordinated adhesive interactions between lymphocyte receptors and endothelial cell adhesion molecules (CAMs) are a prerequisite for effector cell entry into tumor stroma. Whereas the diminished leukocyte-endothelial cell interactions observed in tumor microvessels have been attributed to a reduced expression of endothelial CAMs, there is no quantitative data bearing on this issue. The dual-radiolabeled monoclonal antibody technique was used to quantify constitutive and tumor necrosis factor (TNF)-α-induced expression of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), ICAM-2, P-selectin, E-selectin, and platelet-endothelial cell adhesion molecule 1 (PECAM-1) in different vascular beds of normal (C57Bl/6) and RM-1 tumor-bearing mice. When corrected for endothelial surface area, the constitutive expression of selectins in tumor vessels was higher than that observed in other vascular beds. Both constitutive and induced expression of endothelial CAMs in peripheral vascular beds did not differ between normal and tumor-bearing mice. Within the tumor, the magnitude of the upregulation of P-selectin, ICAM-1, and VCAM-1 after TNF-α was similar to that within other vascular beds. E-selectin expression in tumors was refractory to TNF-α, whereas PECAM-1 and ICAM-2 expression were significantly reduced. Our findings suggest that the presence of a solid tumor does not influence endothelial CAM expression in other vascular beds and that the higher density of selectins in nonstimulated tumor vessels may promote the recruitment of rolling leukocytes in this tissue.