bluuebunny/crossref_metadata_2025 huggingface dataset:
Muscle metaboreflex increases ventricular performance in conscious dogs
Authors: O’Leary Donal S. , Augustyniak Robert A.
Published: December 2017

Ischemia of active skeletal muscle stimulates neuronal afferents within the muscle, which elicits a reflex increase in systemic arterial pressure (SAP), heart rate (HR), and cardiac output (CO) termed the muscle metaboreflex. We investigated whether activation of the muscle metaboreflex elicits increases in ventricular performance using conscious, chronically instrumented dogs trained to run on a treadmill (3.2 km/h, 0% grade). The muscle metaboreflex was activated via progressive partial vascular occlusion of the terminal aorta during control experiments and with HR maintained constant via a pacemaker connected to ventricular electrodes (225 beats/min). In control experiments, hindlimb ischemia elicited substantial increases in SAP, HR, and CO (+53.9 ± 4.3 mmHg, +32.4 ± 4.5 beats/min, and +1.57 ± 0.22 l/min, respectively; all changes P < 0.05), whereas stroke volume (SV) remained unchanged with reflex activation (control 45.9 ± 2.3 vs. 46.1 ± 2.4 ml, P > 0.05). During metaboreflex activation at constant HR, SV significantly increased such that the increases in CO and SAP were not significantly different from control experiments (+1.77 ± 0.56 l/min and +57.4 ± 3.8 mmHg, P > 0.05 vs. control experiments). No significant change in central venous pressure occurred in either experiment, indicating no Frank-Starling effect on SV. We conclude that muscle metaboreflex-induced increases in ventricular contractility act to sustain SV despite decreases in ventricular filling time due to the tachycardia such that the sustained SV coupled with the tachycardia elicits substantial increases in CO that contribute importantly to the reflex increase in SAP.
Role of SR Ca2+-ATPase in contractile dysfunction of myocytes in tachycardia-induced heart failure
Authors: Igarashi-Saito Keiko , Tsutsui Hiroyuki , Yamamoto Shimako , Takahashi Masaru , Kinugawa Shintaro , Tagawa Hirofumi , Usui Makoto , Yamamoto Mitsutaka , Egashira Kensuke , Takeshita Akira
Published: December 2017

Sarcoplasmic reticulum (SR) Ca2+-ATPase gene expression is reduced in the failing myocardium. However, the functional relevance of these changes to myocardial contractility is not yet established. We assessed myocardial contractile function by analyzing sarcomere motion of isolated myocytes and also quantified SR Ca2+regulatory protein gene expression by Northern blot analysis in the same hearts obtained from 10 dogs with pacing-induced heart failure (HF; 240 beats/min, 4 wk) and 7 control dogs. Sarcomere-shortening velocity was depressed in HF myocytes, accompanied by the prolongation of intracellular Ca2+concentration ([Ca2+]i) transient measured by indo 1 fluorescence ratio. SR Ca2+-ATPase mRNA levels (normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA) were significantly depressed in HF, and calsequestrin mRNA was increased. For control and HF dogs, sarcomere-shortening velocity correlated positively with Ca2+-ATPase mRNA levels ( r = 0.73, n = 17, P < 0.01) but not with calsequestrin mRNA. Ca2+-ATPase mRNA levels were correlated with45Ca2+uptake rate by SR, which was also reduced in HF. Moreover, the inhibition of SR Ca2+-ATPase with thapsigargin or cyclopiazonic acid reproduced in normal myocytes the abnormalities observed in HF myocytes, such as depressed contractility and the prolonged [Ca2+]itransient duration. A downregulation of Ca2+-ATPase gene expression and a resultant decrease in Ca2+uptake by SR may be responsible for the contractile dysfunction and the alterations of [Ca2+]itransient in HF.
Dynamic sympathetic regulation of left ventricular contractility studied in the isolated canine heart
Authors: Miyano Hiroshi , Nakayama Yasunori , Shishido Toshiaki , Inagaki Masashi , Kawada Toru , Sato Takayuki , Miyashita Hiroshi , Sugimachi Masaru , Alexander Joe , Sunagawa Kenji
Published: December 2017

We investigated the dynamic sympathetic regulation of left ventricular end-systolic elastance ( E es) using an isolated canine ventricular preparation with functioning sympathetic nerves intact. We estimated the transfer function from both stellate ganglion stimulation to E es and ganglion stimulation to heart rate (HR) for both left and right ganglia by means of the white noise approach and transformed those transfer functions into corresponding step responses. The HR response was much larger with right sympathetic stimulation than with left sympathetic stimulation (4.3 ± 1.4 vs. 0.7 ± 0.6 beats ⋅ min−1 ⋅ Hz−1, P < 0.01). In contrast, the E es responses without pacing were not significantly different between left and right sympathetic stimulation (0.72 ± 0.34 vs. 0.76 ± 0.42 mmHg ⋅ ml−1 ⋅ Hz−1). Fixed-rate pacing significantly decreased the E es response to right sympathetic stimulation (0.53 ± 0.43 mmHg ⋅ ml−1 ⋅ Hz−1, P < 0.01), but not to left sympathetic stimulation (0.67 ± 0.32 mmHg ⋅ ml−1 ⋅ Hz−1, not significant). Although the mechanism by which the sympathetic nervous system regulates cardiac contractility is different depending on whether the left or right sympathetic nerves are activated, this difference does not affect the apparent response of E es to dynamic sympathetic stimulation.
Pertussis toxin abolishes the cardioprotective effect of ischemic preconditioning in intact rat heart
Authors: Schultz Jo El J. , Hsu Anna K. , Barbieri Joseph T. , Li Pin-Lan , Gross Garrett J.
Published: December 2017

It has been previously demonstrated that Gi/oproteins are involved in ischemic preconditioning (IPC) in rabbits and dogs; however, there has been controversy as to the role of Gi/oproteins in IPC in in vivo rat infarct models. Therefore, the role of G proteins in the cardioprotective effect of IPC in a rat infarct model was reevaluated. Cardioprotection as indicated by infarct size (IS) as a percentage of the area at risk (IS/AAR) was determined by triphenyltetrazolium stain. The control group, which was subjected to 30 min of occlusion (Occ) and 2 h of reperfusion (Rep), had an IS/AAR of 46 ± 6%. A single 5-min Occ followed by 10 min of Rep (1× PC) as well as three 5-min Occ periods interspersed with 5 min of Rep (3× PC) markedly reduced IS/AAR (6 ± 1 and 8 ± 1%, respectively). Pretreatment with pertussis toxin (10 μg/kg ip) for 48 h before 1× PC or 3× PC completely abolished their cardioprotective effects (46 ± 5 and 38 ± 4%, respectively). Pertussis toxin had no effect on IS/AAR and did not inactivate Gi/oproteins as assessed by an in vitro ADP-ribosylation assay of heart homogenates. These results demonstrate that the cardioprotective effect of IPC is mediated by a small subpopulation of Gi/oproteins in the intact rat heart.
Ultrastructural effects of intravascularly injected polyethylene glycol-hemoglobin in intestinal mucosa
Authors: Baldwin Ann L. , Wilson Lisa M. , Valeski J. Edward
Published: December 2017

Polyethylene glycol (PEG)-conjugated Hb (PEG-Hb) is being considered as a blood substitute. Previously, we showed that PEG-Hb extravasates rapidly from the intestinal mucosa and causes transient epithelial sloughing, resulting in temporary unimpeded passage of material between the intestinal lumen and the microcirculation. The present study quantifies the time course of factors related to this disturbance. Anesthetized Sprague-Dawley rats (350–450 g) were injected with a bolus of PEG-Hb (10 mg/ml) in saline. Control animals received saline, alone or with Dextran 70 (5 mg/ml). After 2, 8, 15, 60, or 90 min, the small intestine was perfusion fixed for microscopy (4 animals for each time point). Epithelial cell detachment and mucosal mast cell degranulation peaked at 2 and 8–15 min, respectively, but by 90 min were back to normal. Goblet cell secretion increased with time up to 8–15 min, after which it leveled off. Mean interstitial width was significantly greater 8 min after injection than for controls and continued to increase with time. In capillaries, endothelial fenestral diaphragms were replaced by thick, amorphous structures. Mesenteric mast cell degranulation was significantly greater 60–90 min after injection compared with controls. We propose that these results are consistent with intravascular injection of PEG-Hb invoking a transient inflammatory response in the intestine.
Letters to the Editor
Authors: Jeneson J. A. L. , Kushmerick M. J. , Westerhoff H. V.
Published: December 2017

The following is the abstract of the article discussed in the subsequent letter:

Portman, Michael A., Yun Xiao, Ying Song, and Xue-Han Ning. Expression of adenine nucleotide translocator parallels maturation of respiratory control in heart in vivo. Am. J. Physiol. 273 ( Heart Circ. Physiol. 42): H1977–H1983, 1997.—Changes in the relationship between myocardial high-energy phosphates and oxygen consumption in vivo occur during development, implying that the mode of respiratory control undergoes maturation. We hypothesized that these maturational changes in sheep heart are paralleled by alterations in the adenine nucleotide translocator (ANT), which are in turn related to changes in the expression of this gene. Increases in myocardial oxygen consumption (MV˙o2) were induced by epinephrine infusion in newborn (0–32 h, n = 6) and mature sheep (30–32 days, n = 6), and high-energy phosphates were monitored with31P nuclear magnetic resonance. Western blot analyses for the ANT1and the β-subunit of F1-adenosinetriphosphatase (ATPase) were performed in these hearts and additional ( n = 9 total per group) as well as in fetal hearts (130–132 days of gestation, n = 5). Northern blot analyses were performed to assess for changes in steady-state RNA transcripts for these two genes. Kinetic analyses for the31P spectra data revealed that the ADP-MV˙o2relationship for the newborns conformed to a Michaelis-Menten model but that the mature data did not conform to first- or second-order kinetic control of respiration through ANT. Maturation from fetal to mature was accompanied by a 2.5-fold increase in ANT protein (by Western blot), with no detectable change in β-F1-ATPase. Northern blot data show that steady-state mRNA levels for ANT and β-F1-ATPase increased ∼2.5-fold from fetal to mature. These data indicate that 1) respiratory control pattern in the newborn is consistent with a kinetic type regulation through ANT, 2) maturational decreases in control through ANT are paralleled by specific increases in ANT content, and 3) regulation of these changes in ANT may be related to increases in steady-state transcript levels for its gene.
Three-dimensional imaging of vasculature and parenchyma in intact rodent organs with X-ray micro-CT
Authors: Jorgensen Steven M. , Demirkaya Omer , Ritman Erik L.
Published: December 2017

A microcomputed tomography (micro-CT) scanner, which generates three-dimensional (3-D) images consisting of up to a billion cubic voxels, each 5–25 μm on a side, and which has isotropic spatial resolution, is described. Its main components are a spectroscopic X-ray source that produces selectable primary emission peaks at ∼9, 18, or 25 keV and a fluorescing thin crystal plate that is imaged (at selectable magnification) with a lens onto a 2.5 × 2.5-cm, 1,024 × 1,024-pixel, charge-coupled device (CCD) detector array. The specimen is positioned close to the crystal and is rotated in 721 equiangular steps around 360° between each X-ray exposure and its CCD recording. Tomographic reconstruction algorithms, applied to these recorded images, are used to generate 3-D images of the specimen. The system is used to scan isolated, intact, fixed rodent organs (e.g., heart or kidney) with the image contrast of vessel lumens enhanced with contrast medium. 3-D image display and analysis are used to address physiological questions about the internal structure-to-function relationships of the organs.
Human carotid baroreflex during isometric lower arm contraction and ischemia
Authors: Spaak Jonas , Sundblad Patrik , Linnarsson Dag
Published: December 2017

Our aim was to determine the roles of somatomotor activation and muscle ischemia for the tachycardia and hypertension of isometric arm contraction. Carotid-cardiac and carotid-mean arterial pressure (MAP) baroreflex response curves were determined in 10 men during rest, during isometric arm contraction at 30% of maximum, and during postcontraction ischemia. Carotid distending pressure (CDP) was changed by applying pressure and suction in a neck chamber. Pressures ranged from +40 to −80 mmHg and were applied repeatedly for 15 s during the three conditions. Maximum slopes and ranges of the response curves did not differ among conditions. The heart rate (HR) curve was shifted to a 14 ± 1.8 (mean ± SE) beats/min higher HR and a 9 ± 5.7 mmHg higher CDP during contraction and to a 14 ± 5.9 mmHg higher CDP during postcontraction ischemia with no change of HR compared with rest. The MAP curve was shifted to a 20 ± 2.8 mmHg higher MAP and to a 18 ± 5.4 mmHg higher CDP during contraction, and the same shifts were recorded during postcontraction ischemia. We conclude that neither somatomotor activation nor muscle ischemia changes the sensitivity of arterial baroreflexes. The upward shift of the MAP response curve, with no shift of the HR response curve during postexercise ischemia, supports the notion of parallel pathways for MAP and HR regulation in which HR responses are entirely caused by somatomotor activation and the pressor response is mainly caused by muscle ischemia.
Dynamic heart rate variability: a tool for exploring sympathovagal balance continuously during sleep in men
Authors: Otzenberger Hélène , Gronfier Claude , Simon Chantal , Charloux Anne , Ehrhart Jean , Piquard François , Brandenberger Gabrielle
Published: December 2017

We have recently demonstrated that the overnight profiles of cardiac interbeat autocorrelation coefficient of R-R intervals ( r RR) calculated at 1-min intervals are related to the changes in sleep electroencephalographic (EEG) mean frequency, which reflect depth of sleep. Other quantitative measures of the Poincaré plots, i.e., the standard deviation of normal R-R intervals (SDNN) and the root mean square difference among successive R-R normal intervals (RMSSD), are commonly used to evaluate heart rate variability. The present study was designed to compare the nocturnal profiles of r RR, SDNN, and RMSSD with the R-R spectral power components: high-frequency (HF) power, reflecting parasympathetic activity; low-frequency (LF) power, reflecting a predominance of sympathetic activity with a parasympathetic component; and the LF-to-HF ratio (LF/HF), regarded as an index of sympathovagal balance. r RR, SDNN, RMSSD, and the spectral power components were calculated every 5 min during sleep in 15 healthy subjects. The overnight profiles of r RR and LF/HF showed coordinate variations with highly significant correlation coefficients ( P < 0.001 in all subjects). SDNN correlated with LF power ( P < 0.001), and RMSSD correlated with HF power ( P < 0.001). The overnight profiles of r RR and EEG mean frequency were found to be closely related with highly cross-correlated coefficients ( P < 0.001). SDNN and EEG mean frequency were also highly cross correlated ( P < 0.001 in all subjects but 1). No systematic relationship was found between RMSSD and EEG mean frequency. In conclusion, r RR appears to be a new tool for evaluating the dynamic beat-to-beat interval behavior and the sympathovagal balance continuously during sleep. This nonlinear method may provide new insight into autonomic disorders.
β-Adrenergic stimulation causes cardiocyte apoptosis: influence of tachycardia and hypertrophy
Authors: Shizukuda Yukitaka , Buttrick Peter M. , Geenen David L. , Borczuk Alain C. , Kitsis Richard N. , Sonnenblick Edmund H.
Published: December 2017

To establish whether catecholamines per se in the absence of significant increases in systolic load induce myocardial damage via apoptosis, rats were treated with vehicle or isoproterenol (400 μg ⋅ kg−1 ⋅ h−1). Apoptotic cardiocytes (Apo) were identified in paraffin-embedded sections using terminal deoxynucleotide transferase-mediated dUTP nick end labeling. Results were confirmed using an independent ligase assay. Systolic blood pressures were comparable in isoproterenol-treated and control rats. Twenty-four hours of treatment with isoproterenol resulted in significant numbers of Apo compared with control [7.9 ± 2.5 vs. 0.3 ± 0.3 (SE) cm−2, P < 0.05]. A cohort of animals was subjected to ventricular pacing to induce a tachycardia equivalent to that induced by isoproterenol, and these animals did not show an increase in Apo. The left ventricular hypertrophy induced by 2 wk of abdominal aortic banding also increased Apo (∼7.2-fold); however, 24 h of isoproterenol infusion did not induce additional Apo in these rats. Thus catecholamines, in the absence of altered systolic load, induce Apo which is not mediated solely by tachycardia. Left ventricular hypertrophy secondary to abdominal aortic banding is associated with Apo, but this does not increase sensitivity to isoproterenol-induced Apo.
Nitric oxide-independent activation of soluble guanylyl cyclase contributes to endotoxin shock in rats
Authors: Wu Chin-Chen , Chen Shiu-Jen , Yen Mao-Hsiung
Published: December 2017

We investigated whether a complete inhibition of nitric oxide (NO) formation caused by bacterial endotoxin (lipopolysaccharide, LPS) in vivo prevents the hypotension and restores the vascular hyporeactivity to normal in vivo and ex vivo. The combination of dexamethasone (Dex; 3 mg/kg at 30 min before LPS) plus aminoguanidine (AG; 15 mg/kg at 2 h after LPS) inhibited the overproduction of nitrate (an indicator of NO) in the plasma and aortic smooth muscle and also prevented the development of the delayed hypotension in rats treated with LPS for 6 h. However, the vascular hyporeactivity to norepinephrine (NE) was only partially improved either in vivo or ex vivo in endotoxemic rats treated with Dex plus AG. Pretreatment of aortic rings with Nω-nitro-l-arginine methyl ester (l-NAME) or 1 H-[1,2,4]oxidazolo[4,3-a]quinoxalin-1-one (ODQ) enhanced the contraction to NE in rings obtained from LPS-treated rats, but not in those from Dex plus AG-treated endotoxemic rats. Methylene blue, an inhibitor of soluble guanylyl cyclase (GC), completely restored contractions to NE and aortic cGMP levels to normal either in LPS-treated rats or in Dex plus AG-treated endotoxemic rats, whereas the cGMP level was partially inhibited by ODQ in LPS-treated rats only. These results suggest that non-NO mediator(s) also activates soluble GC during endotoxemia. Interestingly, we found that in the presence of tetraethylammonium (an inhibitor of K+channels) plusl-NAME or charybdotoxin [a specific inhibitor of large-conductance Ca2+-activated K+(KCa) channels] plus ODQ, the vascular hyporeactivity to NE in the LPS-treated group was also completely restored to normal. In addition, in the presence ofl-NAME or ODQ, the vascular hyporeactivity to high K+was abolished in rings from the LPS-treated group. These results suggest that LPS causes the production of other mediator(s), in addition to NO, which also stimulates soluble GC (i.e., increases the formation of cGMP) and then activates the large-conductance KCachannels in the vascular smooth muscle causing vascular hyporeactivity.
Capillaries and arterioles are electrically coupled in hamster cheek pouch
Authors: Beach James M. , McGahren Eugene D. , Duling Brian R.
Published: December 2017

In this report we demonstrate electrical communication in the microcirculation between arterioles and capillary networks in situ. Microvessel networks in the hamster cheek pouch, which included capillaries and their feeding arterioles, were labeled with the voltage-sensitive dye di-8-ANEPPS by intraluminal perfusion through a micropipette. Pulses of 140 mM potassium solution were applied by pressure ejection from micropipettes positioned on arterioles several hundred micrometers upstream from capillaries. Potassium caused membrane potential changes of 3–11 mV in capillary segments up to 1,200 μm distal to the stimulation site, with time delays of <1 s. Capillary membrane potential changes were biphasic, with initial depolarizations followed by hyperpolarizations. The size of the response decreased exponentially with the distance between the arteriole and capillary, with a 1/e distance of 590 μm. The time to peak depolarization of both arteriolar and capillary segments was similar. The time to peak response was significantly faster than that for responses from direct stimulation of capillaries. Capillary responses were also obtained when blood flow was either blocked or directed toward sites of stimulation. Acetylcholine (10−4 M) and phenylephrine (10−5 M) applied to the arterioles by iontophoresis produced monophasic hyperpolarizing and depolarizing responses, respectively, in capillaries with <1-s delay between stimulus and onset of the membrane potential change. These results provide evidence in situ of a pathway for electrical communication between arteriolar and capillary levels of the microcirculation.
Renal ischemia preconditions myocardium: role of adenosine receptors and ATP-sensitive potassium channels
Authors: Pell Theresa J. , Baxter Gary F. , Yellon Derek M. , Drew G. Michael
Published: December 2017

Brief renal ischemia-reperfusion is reported to precondition the myocardium; however, the underlying mechanisms are unknown. This phenomenon was, therefore, investigated using an in vivo rabbit model of acute myocardial infarction. Characterization of the mechanisms involved was performed using the nonselective adenosine receptor antagonist 8-( p-sulfophenyl)theophylline (8-SPT) and the ATP-sensitive potassium (KATP) channel blocker sodium 5-hydroxydecanoate (5-HD). Pentobarbital-anesthetized rabbits underwent a left thoracotomy and pericardiotomy. A laparotomy was then performed to expose the left renal artery. Animals were either preconditioned with a 10-min occlusion of the renal artery followed by 10 min of reperfusion or underwent a 20-min sham period of anesthesia. Subsequently, the left coronary artery was then occluded for 30 min and reperfused for 2 h. Infarct-to-risk ratio was limited from 32.7 ± 4.0% ( n = 12) in controls to 17.8 ± 3.0% ( n = 9; P = 0.002) in preconditioned hearts. Protection was abolished by 7.5 mg/kg iv 8-SPT (36.7 ± 3.7%; n = 6) or 5 mg/kg iv 5-HD (33.1 ± 4.4%; n = 6) administered before preconditioning. 8-SPT (40.0 ± 4.4%; n = 6) or 5-HD (40.5 ± 4.2%; n = 6) did not affect infarct-to-risk ratio in sham controls. Thus activation of both adenosine receptors and KATP channels appears to be involved in acute renal preconditioning of the myocardium.
Metabotropic glutamate receptors depress vagal and aortic baroreceptor signal transmission in the NTS
Authors: Liu Zhi , Chen Chao-Yin , Bonham Ann C.
Published: December 2017

We sought to determine whether metabotropic glutamate receptors contribute to frequency-dependent depression of vagal and aortic baroreceptor signal transmission in the nucleus of the solitary tract (NTS) in vivo. In α-chloralose-anesthetized rabbits, we determined the number of extracellular action potentials synaptically evoked by low (1 Hz)- or high-frequency vagal (3–20 Hz) or aortic depressor nerve (ADN) (6–80 Hz) stimulation and postsynaptically evoked by the ionotropic glutamate receptor agonist α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). The metabotropic glutamate receptor agonist (2 S,1′ S,2′ S)-2-(carboxycyclopropyl)glycine (L-CCG-I) attenuated NTS responses monosynaptically evoked by 1-Hz vagus stimulation by 34% ( n = 25; P = 0.011), while augmenting AMPA-evoked responses by 64% ( n = 17; P = 0.026). The metabotropic glutamate receptor antagonist α-methyl-4-phosphonophenylglycine (MPPG) did not affect NTS responses to low-frequency vagal stimulation ( n = 11) or AMPA ( n = 10) but augmented responses to high-frequency stimulation by 50% ( n= 25; P = 0.0001). MPPG also augmented NTS responses to high-frequency ADN stimulation by 35% ( n = 9; P = 0.048) but did not affect responses to low-frequency stimulation ( n = 9) or AMPA ( n = 7). The results suggest that metabotropic glutamate receptors, presumably at presynaptic sites, contribute to frequency-dependent depression of vagal and aortic baroreceptor signal transmission in NTS.
Ultrarapid delayed rectifier current inactivation in human atrial myocytes: properties and consequences
Authors: Feng Jianlin , Xu Donghui , Wang Zhiguo , Nattel Stanley
Published: December 2017

The ultrarapid delayed rectifier current ( I K,ur) plays a significant role in human atrial repolarization and is generally believed to show little rate dependence because of slow and partial inactivation. This study was designed to evaluate in detail the properties and consequences of I K,urinactivation in isolated human atrial myocytes. I K,ur inactivated with a biexponential time course and a half-inactivation voltage of −7.5 ± 0.6 mV (mean ± SE), with complete inactivation during 50-s pulses to voltages positive to +10 mV (37°C). Recovery from inactivation proceeded slowly, with time constants of 0.42 ± 0.06 and 7.9 ± 0.9 s at −80 mV (37°C). Substantial frequency dependence was observed at 37°C over a clinically relevant range of frequencies. Inactivation was faster and occurred at more positive voltages at 37°C compared with room temperature. The voltage and time dependencies of Kv1.5 inactivation were studied in Xenopus oocytes to avoid overlapping currents and strongly resembled those of I K,ur in native myocytes. We conclude that, while I K,urinactivation is slow, it is extensive, and slow recovery from inactivation confers important frequency dependence with significant consequences for understanding the role of I K,ur in human atrial repolarization.
Independent inhibition of calcineurin and K+currents by the immunosuppressant FK-506 in rat ventricle
Authors: duBell W. H. , Gaa S. T. , Lederer W. J. , Rogers T. B.
Published: December 2017

FK-506 increases the cytosolic Ca2+concentration transient in rat ventricular myocytes by prolonging the action potential through inhibition of the K+currents Itoand IK[ J. Physiol. (Lond.) 501: 509–516, 1997]. Physiological and biochemical techniques were used in parallel to examine the electrophysiological mechanisms and the role of calcineurin inhibition in these effects. FK-506 prolonged the recovery of Itofrom inactivation. Thus Itoinhibition was frequency dependent, with no decrease at 0.2 Hz (recorded at +50 mV from −70 mV) but a 40% decrease at 2.0 Hz. In contrast, inhibition of IK(∼60%) was time and voltage independent. At 25 μM, FK-506 (by 65%) and cyclosporin A (by 57%) inhibited calcineurin activity in myocyte extracts. However, only FK-506 increased the cytosolic Ca2+concentration transient in field-stimulated myocytes. Furthermore, FK-506 was still active on K+currents when cells were dialyzed with 10 mM EGTA. These results demonstrate that calcineurin inhibition is not responsible for the functional effects of FK-506 in heart and suggest that IKand Itoare modulated by FK-506-binding proteins or directly by FK-506.
Pattern of substrate utilization in vascular smooth muscle using 13C isotopomer analysis of glutamate
Authors: Allen Tara M. , Hardin Christopher D.
Published: December 2017

Although vascular smooth muscle (VSM) derives the majority of its energy from oxidative phosphorylation, controversy exists concerning which substrates are utilized by the tricarboxylic acid (TCA) cycle. We used 13C isotopomer analysis of glutamate to directly measure the entry of exogenous [13C]glucose and acetate and unlabeled endogenous sources into the TCA cycle via acetyl-CoA. Hog carotid artery segments denuded of endothelium were superfused with 5 mM [1-13C]glucose and 0–5 mM [1,2-13C]acetate at 37°C for 3–12 h. We found that both resting and contracting VSM preferentially utilize [1,2-13C]acetate compared with [1-13C]glucose and unlabeled substrates. The entry of glucose into the TCA cycle (30–60% of total entry via acetyl-CoA) exhibited little change despite alterations in contractile state or acetate concentrations ranging from 0 to 5 mM. We conclude that glucose and nonglucose substrates are important oxidative substrates for resting and contracting VSM. These are the first direct measurements of relative substrate entry into the TCA cycle of VSM during activation and may provide a useful method to measure alterations in VSM metabolism under physiological and pathophysiological conditions.
Osteopontin inhibits inducible nitric oxide synthase activity in rat vascular tissue
Authors: Scott Jeremy A. , Weir M. Lynn , Wilson Sylvia M. , Xuan Jim W. , Chambers Ann F. , McCormack David G.
Published: December 2017

We tested the hypothesis that osteopontin (OPN) can inhibit the induction of inducible nitric oxide synthase (iNOS) in vascular tissue. iNOS activity was induced in rat thoracic aortas by incubation of the tissue with lipopolysaccharide (LPS) and measured by conversion ofl-[3H]arginine tol-[3H]citrulline. Addition of ≥1 nM recombinant OPN protein significantly reduced the LPS-induced increase in iNOS activity. Western blotting and the RT-PCR were used to determine the effect of LPS with and without OPN on tissue levels of iNOS protein and RNA, respectively. LPS resulted in an increase in iNOS protein and RNA, whereas OPN dose-dependently reduced tissue levels of iNOS activity, protein, and RNA. Mutated OPN proteins, in which the integrin-binding RGD amino acid sequence was deleted or mutated to RGE, resulted in complete and partial loss, respectively, of the ability of OPN to inhibit LPS-induced iNOS activity, implicating integrin binding in the effect. These results indicate that OPN can prevent induction of iNOS in vascular tissue.
Depression of excitability by sphingosine 1-phosphate in rat ventricular myocytes
Authors: MacDonell Karen L. , Severson David L. , Giles Wayne R.
Published: December 2017

Sphingosine 1-phosphate (S-1- P) is a bioactive sphingolipid that is released from activated platelets. Extracellular S-1- P augments an inwardly rectifying potassium conductance in cultured atrial preparations, but the electrophysiological effects of this compound in the ventricle are unknown. The electrophysiological effects of S-1- P were examined in single myocytes from rat ventricular muscle. Action potential waveforms and underlying ionic currents in the presence and absence of 3 μM S-1- P (1–6 min) were recorded. S-1- P increased the minimum stimulus current needed to elicit an action potential by ∼100 pA. Pertussis toxin or preexposure to S-1- P did not alter this effect. The action potential waveform was unchanged by S-1- P. The inward sodium current ( I Na) was examined in a range of membrane potentials just negative to the potential for firing an action potential. S-1- P reversibly inhibited peak I Na by ∼50 pA, whereas the inward rectifier potassium current was not significantly changed. The results of this study suggest that S-1- P inhibits rat ventricular excitability by reducing I Na.
Role of tyrosine phosphorylation in the regulation of cerebral vascular tone in newborn pig in vivo
Authors: Parfenova Helena , Fedinec Alex , Leffler Charles W.
Published: December 2017

The role of tyrosine phosphorylation was investigated using protein tyrosine phosphatase inhibitors in newborn pigs equipped with a cranial window in vivo. We tested the hypothesis that cyclooxygenase and nitric oxide (NO) synthase are physiological targets for tyrosine phosphorylation in cerebral circulation. Phenylarsine oxide dilated pial arterioles and increased prostacyclin and prostaglandin E2 in cortical periarachnoid fluid; these responses were inhibited by indomethacin. N ω-nitro-l-arginine methyl ester (l-NAME) and N ω-nitro-l-arginine (l-NNA) inhibited the vasodilation to phenylarsine oxide; the effects of NO synthase inhibitors and indomethacin were additive. Cyclooxygenase-mediated vascular responses were assessed using topical application of arachidonic acid. Phenylarsine oxide and sodium orthovanadata potentiated vasodilation and prostanoid synthesis in response to arachidonic acid. N ω-nitro-l-arginine methyl ester and N ω-nitrol-arginine did not affect vasodilation or prostanoid production in response to arachidonic acid, indicating no cross talk between cyclooxygenase and NO synthase. These data indicate that cyclooxygenase and NO synthase are physiological targets for tyrosine phosphorylation in the cerebral circulation of newborn pigs.
Postexercise hypotension is mediated by reductions in sympathetic nerve activity
Authors: Kulics Jennifer M. , Collins Heidi L. , DiCarlo Stephen E.
Published: December 2017

Mean arterial pressure (MAP), the product of cardiac output (CO) and total peripheral resistance (TPR), is reduced below preexercise levels after a single bout of mild to moderate dynamic exercise. Thus acute, dynamic exercise may be used as a safe, therapeutic approach to reduce MAP. However, the mechanisms responsible for the postexercise hypotension (PEH) are unknown. We tested the hypothesis that PEH is associated with reductions in TPR and sympathetic nerve activity (SNA). Two experimental protocols were designed to test this hypothesis in male spontaneously hypertensive rats (SHR). In protocol 1( n = 9), CO and TPR were determined before, during, and after exercise. In protocol 2 ( n = 7), lumbar SNA (LSNA) was recorded before and after exercise. Rats in protocol 1 were chronically instrumented with left carotid arterial catheters and ascending aortic Doppler ultrasonic flow probes. Rats in protocol 2 were chronically instrumented with left carotid arterial catheters and electrodes around the lumbar sympathetic trunk. Dynamic treadmill exercise (9–12 m/min, 10% grade for 40 min) resulted in a postexercise reduction in MAP (from 143 ± 5 to 128 ± 4 mmHg, P < 0.05). Associated with the PEH was a reduction in TPR (from 28 ± 3 to 19 ± 2 mmHg/kHz; P < 0.05) and an elevation in CO (from 5.7 ± 0.4 to 7.2 ± 0.5 kHz; P < 0.05). The reductions in arterial pressure and TPR were associated with a decrease in LSNA (from 98 ± 3 to 49 ± 6%; P < 0.05). These results suggest that PEH is mediated by reductions in TPR and SNA.
Metabolism of cAMP to adenosine: role in vasodilation of rat pial artery in response to hypotension
Authors: Hong Ki Whan , Shin Hwa Kyoung , Kim Hyung Hwan , Choi Jae Moon , Rhim Byung Yong , Lee Won Suk
Published: December 2017

The purpose of this experiment was to examine whether the cAMP-adenosine pathway is implicated in the autoregulatory vasodilation in response to hypotension. Suffusion with cAMP (1–100 μmol/l) or adenosine (0.01–10 μmol/l) caused a sustained vasodilation of the resting pial arteries in a concentration-dependent manner. In contrast, N6,2′- O-dibutyryl-cAMP and 8-bromo-cAMP exerted a weak dilation at high concentration (100 μmol/l). The vasodilation to cAMP (1–100 μmol/l), adenosine (0.01–10 μmol/l), and hypotension was significantly reduced by pretreatment with 3,7-dimethyl-1-propargylxanthine (1 μmol/l), an A2receptor antagonist, as well as 3-isobutyl-1-methylxanthine (3 μmol/l), an inhibitor of endo- and ectophosphodiesterase, 1,3-dipropyl-8- p-sulfophenylxanthine (100 μmol/l), an inhibitor of ecto-5′-phosphodiesterase, or α,β-methylene-adenosine 5′-diphosphate (100 μmol/l), an inhibitor of ecto-5′-nucleotidase. However, 8-cyclopentyltheophylline (1 μmol/l), an A1antagonist, did not elicit a similar response. The increased release of adenosine when the cortical surface was suffused with cAMP (100 μmol/l) was significantly reduced by 3-isobutyl-1-methylxanthine, 1,3-dipropyl-8- p-sulfophenylxanthine, and α,β-methylene-adenosine 5′-diphosphate (each 100 μmol/l). These results indicate that the cAMP-adenosine pathway as a viable metabolic mechanism is implicated in the production of adenosine in the rat pial artery and contributes to the regulation of vasodilation in response to hypotension.
Use of pulse pressure method for estimating total arterial compliance in vivo
Authors: Stergiopulos N. , Segers P. , Westerhof N.
Published: December 2017

We determined total arterial compliance from pressure and flow in the ascending aorta of seven anesthetized dogs using the pulse pressure method (PPM) and the decay time method (DTM). Compliance was determined under control and during occlusion of the aorta at four different locations (iliac, renal, diaphragm, and proximal descending thoracic aorta). Compliance of PPM gave consistently lower values (0.893 ± 0.015) compared with the compliance of DTM (means ± SE; r = 0.989). The lower compliance estimates by the PPM can be attributed to the difference in mean pressures at which compliance is determined (mean pressure, 81.0 ± 3.6 mmHg; mean diastolic pressure, over which the DTM applies, 67.0 ± 3.6 mmHg). Total arterial compliance under control conditions was 0.169 ± 0.007 ml/mmHg. Compliance of the proximal aorta, obtained during occlusion of the proximal descending aorta, was 0.100 ± 0.007 ml/mmHg. Mean aortic pressure was 80.4 ± 3.6 mmHg during control and 102 ± 7.7 mmHg during proximal descending aortic occlusion. From these results and assuming that upper limbs and the head contribute as little as the lower limbs, we conclude that 60% of total arterial compliance resides in the proximal aorta. When we take into account the inverse relationship between pressure and compliance, the contribution of the proximal aorta to the total arterial compliance is even more significant.
Human endothelial cells produce orosomucoid, an important component of the capillary barrier
Authors: Sörensson Jenny , Matejka Göran L. , Ohlson Maria , Haraldsson Börje
Published: December 2017

The serum protein orosomucoid (α1-acid glycoprotein) is needed to maintain the high capillary permselectivity required for normal homeostasis. It is not known how the protein executes its action, but it seems to contribute to the charge barrier. Moreover, recent studies suggest that the endothelial glycocalyx is essential for the charge barrier. The main site of orosomucoid synthesis is the liver, but we wanted to explore the possibility that orosomucoid was synthesized in endothelial cells. Primary cultures of human microvascular endothelial cells (HMVEC) from dermal tissue were established. Human liver cells were used as positive controls, and total RNA was prepared from both cell types. Reverse transcription-polymerase chain reaction (RT-PCR) was performed and demonstrated orosomucoid expression. After RT-PCR, the identities of the PCR products were confirmed by sequencing. RNase protection assay performed on total RNA from the HMVEC confirmed the results from the RT-PCR, i.e., orosomucoid mRNA is expressed by endothelial cells. Synthesis of orosomucoid in both liver and endothelial cells was demonstrated by immunoprecipitation. In conclusion, endothelial cells normally produce orosomucoid, which is essential for capillary charge selectivity. We suggest that orosomucoid exerts its effect by interacting with other components of the endothelial glycocalyx.
Extracellular signal-regulated kinases 1 and 2 activation in endothelial cells exposed to cyclic strain
Authors: Ikeda Masataka , Takei Teiji , Mills Ira , Kito Hiroyuki , Sumpio Bauer E.
Published: December 2017

The aim of this study was to determine whether extracellular signal-regulated kinases 1/2 (ERK1/ERK2) are activated and might play a role in enhanced proliferation and morphological change induced by strain. Bovine aortic endothelial cells (BAEC) were subjected to an average of 6 or 10% strain at a rate of 60 cycles/min for up to 4 h. Cyclic strain caused strain- and time-dependent phosphorylation and activation of ERK1/ERK2. Peak phosphorylation and activation of ERK1/ERK2 induced by 10% strain were at 10 min. A specific ERK1/ERK2 kinase inhibitor, PD-98059, inhibited phosphorylation and activation of ERK1/ERK2 but did not inhibit the increased cell proliferation and cell alignment induced by strain. Treatment of BAEC with 2,5-di- tert-butyl-1,4-benzohydroquinone, to deplete inositol trisphosphate-sensitive calcium storage, and gadolinium chloride, a Ca2+channel blocker, did not inhibit the activation of ERK1/ERK2. Strain-induced ERK1/ERK2 activation was partly inhibited by the protein kinase C inhibitor calphostin C and completely inhibited by the tyrosine kinase inhibitor genistein. These data suggest that 1) ERK1/ERK2 are not critically involved in the strain-induced cell proliferation and orientation, 2) strain-dependent activation of ERK1/ERK2 is independent of intracellular and extracellular calcium mobilization, and 3) protein kinase C activation and tyrosine kinase regulate strain-induced activation of ERK1/ERK2.
Effect of estrogen on aortic function in postmenopausal women
Authors: Stefanadis Christodoulos , Tsiamis Eleftherios , Dernellis John , Toutouzas Pavlos
Published: December 2017

We hypothesized that estrogen may alter aortic elastic properties. The aortic pressure-diameter relation was obtained in 20 postmenopausal women, 10 without ( group 1) and 10 with ( group 2) proven coronary artery disease, before and after intravenous administration of 10 μg of 17β-estradiol. Instantaneous aortic diameter was measured by an intravascular catheter developed in our institution simultaneously with aortic pressure at the same aortic level with a catheter-tipped micromanometer. At baseline, elastic properties of the aorta were decreased in group 2 compared with group 1. Compared with baseline, aortic distensibility was increased in both groups ( P< 0.01 and P < 0.05 for groups 1 and 2, respectively) after estrogen administration, whereas the pressure-diameter loop was shifted downward along a different hypothetical line of elasticity, suggesting active changes in the aortic elastic properties. Furthermore, a significant reduction in wave reflection was found in both groups ( P < 0.001). This action may contribute to the beneficial effects of estrogen on the cardiovascular system and may have future therapeutic implications in postmenopausal women.
Relative contribution of vasodilator prostanoids and NO to metabolic vasodilation in the human forearm
Authors: Duffy Stephen J. , New Gishel , Tran Binh T. , Harper Richard W. , Meredith Ian T.
Published: December 2017

Although many factors are thought to contribute to the regulation of metabolic vasodilation in skeletal muscle vasculature, recent interest has focused on the role of the endothelium. We examined the relative roles of nitric oxide (NO) and of vasodilator prostanoids in the control of metabolically induced functional hyperemia in the forearm of humans. In 43 healthy volunteers [24 ± 5 (SD) yr] we assessed resting and functional hyperemic blood flow (FHBF) in response to 2 min of isotonic forearm exercise before and after inhibition of NO and/or vasodilator prostanoid production with intra-arterial N G-monomethyl-l-arginine (l-NMMA, 2 mg/min) and aspirin (ASA, 3 mg/min), respectively. Blood flow was measured using venous occlusion plethysmography.l-NMMA and ASA decreased resting forearm blood flow by 42% ( P < 0.0001) and 23% ( P < 0.0001), respectively, whereas infusion of ASA followed byl-NMMA reduced flow by a further 24% ( P < 0.05).l-NMMA reduced peak FHBF by 18% [from 13.9 ± 1.0 to 11.4 ± 1.1 (SE) ml ⋅ 100 ml forearm−1 ⋅ min−1, P = 0.003] and the volume “repaid” after 1 and 5 min by 25% (8.9 ± 0.7 vs. 6.7 ± 0.7 ml/100 ml, P < 0.0001) and 37% (26.6 ± 1.8 vs. 16.8 ± 1.6 ml/100 ml, P < 0.0001). ASA similarly reduced peak FHBF by 19% (from 14.5 ± 1.1 to 11.8 ± 0.9 ⋅ 100 ml forearm−1 ⋅ min−1, P < 0.001) and the volume repaid after 1 and 5 min by 14% (7.5 ± 0.6 vs. 6.4 ± 0.6 ml/100 ml, P = 0.0001) and 20% (21.2 ± 1.5 vs. 16.9 ± 1.5 ml/100 ml, P < 0.0001), respectively. The coinfusion of ASA andl-NMMA did not decrease FHBF to a greater extent than either agent alone. These data suggest that endothelium-derived NO and vasodilator prostanoids contribute to resting blood flow and metabolic vasodilation in skeletal muscle vasculature in healthy humans. Although these vasodilator mechanisms operate in parallel in exercise-induced hyperemia, they appear not to be additive. Other mechanisms must also be operative in metabolic vasodilation.
Real-time measurement of cardiac vagal tone in conscious dogs
Authors: Little C. J. L. , Julu P. O. O. , Hansen S. , Reid S. W. J.
Published: December 2017

Rapid changes in heart rate are caused by changes in parasympathetic tone. The NeuroScope is an electronic device designed to offer an objective real-time measure of instantaneous cardiac vagal tone by phase demodulation of a high-resolution time domain of R-R wave intervals. Data are displayed against an arbitrary but linear scale, the cardiac index of parasympathetic activity (CIPA). To validate this method, 10 conscious healthy dogs were each given six incremental doses of atropine (0.01 mg/kg) to a total dose of 0.06 mg/kg or equal volumes of saline. A dose-response curve was constructed. At the maximum dose of atropine, CIPA values fell to 1.3 ± 0.7% (SD) of baseline, whereas R-R intervals fell to 51.5 ± 11.5% of baseline, and standard deviation of the R-R wave interval fell to 10.6 ± 6.5% of baseline. These findings show that the NeuroScope can provide a specific real-time index of cardiac vagal tone in dogs without need for recourse to atropine.
Flow regulation of ecNOS and Cu/Zn SOD mRNA expression in porcine coronary arterioles
Authors: Woodman Christopher R. , Muller Judy M. , Rush James W. E. , Laughlin M. Harold , Price Elmer M.
Published: December 2017

The purpose of this study was to test the hypothesis that increased flow through coronary arterioles increases endothelial cell nitric oxide synthase (ecNOS) and Cu/Zn superoxide dismutase (SOD) mRNA expression. Single porcine coronary arterioles (ID 100–160 μm; pressurized) were cannulated, perfused, and exposed to intraluminal flow sufficient to produce maximal flow-induced dilation of coronary arterioles (high flow; 7.52 ± 0.22 μl/min), low flow (0.84 ± 0.05 μl/min), or no flow for 2 or 4 h. Mean shear stress was calculated to be 5.7 ± 1.0 dyn/cm2 for high-flow arterioles and 1.6 ± 1.0 dyn/cm2 for low-flow arterioles. At the end of the treatment period, mRNA was isolated from each vessel, and ecNOS and SOD mRNA expression was assessed using a semiquantitative RT-PCR. All data were standardized by coamplifying ecNOS or SOD with glyceraldehyde-3-phosphate dehydrogenase. The results indicate that ecNOS mRNA expression is increased in arterioles exposed to 2 or 4 h of high flow. In contrast, SOD mRNA expression was increased only after 4 h of high flow. Neither gene is induced by exposure to low flow. On the basis of these data, we concluded that ecNOS and SOD mRNA expression is regulated by flow in porcine coronary arterioles. In addition, we concluded that a threshold level of flow and shear stress must be sustained to elicit the upregulation of ecNOS and SOD mRNA expression.