bluuebunny/crossref_metadata_2025 huggingface dataset:
Spinal cord regulation of sympathetic activity in intact and spinal rats
Authors: Hong Y. , Cechetto D. F. , Weaver L. C.
Published: December 2017

Excitatory amino acid (EAA) and cholinergic neurotransmission in the spinal cord of urethan-anesthetized rats was investigated to assess mechanisms regulating sympathetic activity after spinal cord injury. Blockade of EAA transmission by intrathecal injection of kynurenic acid decreased arterial blood pressure by 24 +/- 4 mmHg, heart rate by 15 +/- 10 beats/min, and renal sympathetic nerve activity (RSNA) by 85 +/- 4% in intact rats. In rats with cervical spinal transections, this blockade decreased RSNA by 51 +/- 5% and had no effect on arterial pressure and heart rate. Muscarinic blockade by intrathecal atropine decreased RSNA by 12 +/- 3 and 32 +/- 6% in intact and spinal rats, respectively, and caused no cardiovascular responses in either group. Combined blockade of EAA and muscarinic receptors in spinal rats decreased RSNA by 77 +/- 1%. Intrathecal injections of the EAA agonist D,L-homocysteic acid in spinal rats caused initial increases (335 +/- 28%) in RSNA lasting approximately 3 min and later sustained increases (157 +/- 19%) lasting 36 +/- 8 min. Only the early excitation increased arterial pressure by 17 +/- 3 mmHg, and then pressure returned to baseline values. The EAA agonist kainic acid increased RSNA by 402 +/- 90% in spinal rats, an effect lasting 70 +/- 5 min, and increased arterial pressure by only 8 +/- 2 mmHg for 12 +/- 5 min. These findings suggest that tonic activity of spinal neurons with EAA and cholinergic receptors maintains tonic RSNA after spinal cord transection. However, this activity does not play a major role in maintaining arterial pressure, even if it is increased substantially by EAA receptor stimulation.
Role of tumor necrosis factor-alpha in acute hypovolemic hemorrhagic shock in rats
Authors: Zingarelli B. , Squadrito F. , Altavilla D. , Calapai G. , Di Rosa M. , Caputi A. P.
Published: December 2017

Hemorrhagic shock was induced in male anesthetized rats by intermittently withdrawing blood from an iliac catheter until mean arterial blood pressure (MAP) fell and stabilized within the range of 20-30 mmHg. Survival rate, MAP, and serum and macrophage levels of tumor necrosis factor-alpha (TNF-alpha) were then evaluated. Furthermore, in ex vivo studies, the responsiveness to phenylephrine (PE; 1 nM to 10 microM) was investigated in aortic rings from hemorrhagic shocked rats. Antibodies raised against TNF-alpha (anti-TNF-alpha; 2 mg/kg) or vehicle (phosphate-buffered saline, 1 ml/kg) were injected intravenously 3 h before the bleeding. Vehicle-treated rats, subjected to hemorrhagic shock, exhibited acute and serious hypotension (MAP = 20-30 mmHg) and high levels of serum (790 +/- 47 pg/ml) and macrophage (78 +/- 9 pg/ml) TNF-alpha and died within 30 min. Moreover, aortas from shocked rats showed a marked hypocontractility to PE compared with the reactivity of aortas from a group of sham shocked rats. Anti-TNF-alpha administration significantly improved survival rate and MAP in hypovolemic shocked rats. Furthermore, the hyporesponsiveness to PE was significantly restored in aortic rings. Therefore, these data suggest that TNF-alpha is an important mediator in the pathophysiology of hypovolemic hemorrhagic shock and it might be responsible, at least in part, for the vascular hyporeactivity of this experimental circulatory shock.
Preconditioning in isolated superfused rabbit papillary muscles
Authors: Walker D. M. , Marber M. S. , Walker J. M. , Yellon D. M.
Published: December 2017

Preconditioning has only been demonstrated in arterially perfused myocardium. Our aim was to develop a model of preconditioning in isolated, superfused, isometrically contracting rabbit right ventricular papillary muscle. This would eventually allow us to evaluate isolated human muscles. Papillary muscles were suspended in an organ bath, superfused with oxygenated Tyrode solution, and field stimulated at 1 Hz. Muscles were assigned either to control or to preconditioning groups. Preconditioning was induced with 3 min of rapid pacing (3 Hz) with substrate-free hypoxic buffer and was followed by 15 min of reoxygenation with substrate. Subsequently, both groups were exposed to 45 min of substrate-free hypoxia followed by 120 min of reoxygenation with substrate. Preconditioning protected the myocardium with better recovery of developed force (50.6 +/- 6.7 vs. 27.4 +/- 4.2% of baseline developed force, P < 0.01). This effect could be blocked by 8-(p-sulfophenyl)theophylline (SPT) given during preconditioning at a dose that did not increase hypoxic damage in controls (percent developed force compared to baseline: preconditioned muscles + SPT = 30.9 +/- 2.8% and control muscles + SPT = 27.1 +/- 2.3%). In addition, pretreatment with (-)N6(2-phenylisopropyl)adenosine similarly protected the myocardium (49.5 +/- 5.5% recovery, P < 0.01). We conclude that isolated superfused muscles can be preconditioned. This preconditioning does not depend on coronary flow and involves activation of adenosine receptors.
Basic fibroblast growth factor enhances myocardial collateral flow in a canine model
Authors: Unger E. F. , Banai S. , Shou M. , Lazarous D. F. , Jaklitsch M. T. , Scheinowitz M. , Correa R. , Klingbeil C. , Epstein S. E.
Published: December 2017

Basic fibroblast growth factor (FGF) is a multifunctional peptide that may play an integral role in angiogenesis associated with coronary collateral formation and myocardial infarct healing. We sought to determine the effects of exogenously administered basic FGF on collateral blood flow to ischemic myocardium. Ameroid constrictors were used to cause gradual occlusion of the left circumflex coronary artery in dogs. Basic FGF (110 micrograms, n = 9) or saline (n = 12) was given as a daily bolus injection directly into the collateral-dependent zone, beginning 10 days after placement of the Ameroid and continuing for 28 days. Collateral flow was assessed weekly as the ratio of collateral to normal zone (CZ/NZ) blood flow during maximal pharmacologically induced coronary vasodilation. The CZ/NZ increased in both treated and control dogs as a function of time; however, transmural collateral flow in basic FGF-treated dogs significantly exceeded that of control dogs by the second week of treatment. Final CZ/NZ blood flow ratios were 0.49 +/- 0.05 and 0.35 +/- 0.02 in the treated and control groups, respectively (means +/- SE, P = 0.0002). Treatment with basic FGF was also associated with significant increases in the numerical density of distribution vessels and endothelial cell DNA synthesis within the CZ. We also found that basic FGF had acute effects as a coronary vasodilator. Thus exogenous administration of basic FGF enhances maximal collateral blood flow in dogs with myocardial ischemia secondary to single-vessel coronary occlusion, an effect that is likely mediated through the direct angiogenic effects of the peptide, although its acute vasodilatory effects may also play a role.
Relation of principal components of ECG maps to loci of wall motion abnormality in old myocardial infarction
Authors: Endo T. , Yamaki M. , Ikeda H. , Kubota I. , Tomoike H.
Published: December 2017

The purpose of this study was to examine the correlation between body surface potential distribution and the extent of abnormally contracting segments (ACS) of the left ventricle in patients with old myocardial infarction (MI). Body surface potential distribution was quantitatively analyzed using principal component analysis. The first six principal components were extracted from data set obtained from both 25 normal subjects and 100 patients. The z scores (principal component weights) were calculated in a time domain at every 4 or 8 ms in another 81 patients with previous MI. In anterior MI, the second z scores on T wave and the fourth z scores on QRS complex were significantly lower in the presence than in the absence of ACS at the lateral wall. In inferior MI, the first z scores on QRS complex, the second on T wave, and the third on both Q and T represented significant differences between the presence and the absence of ACS at the posterior wall. Minute differences in the extent of ACS were sensitively and noninvasively detected on z scores of principal components.
Physiological time-series analysis: what does regularity quantify?
Authors: Pincus S. M. , Goldberger A. L.
Published: December 2017

Approximate entropy (ApEn) is a recently developed statistic quantifying regularity and complexity that appears to have potential application to a wide variety of physiological and clinical time-series data. The focus here is to provide a better understanding of ApEn to facilitate its proper utilization, application, and interpretation. After giving the formal mathematical description of ApEn, we provide a multistep description of the algorithm as applied to two contrasting clinical heart rate data sets. We discuss algorithm implementation and interpretation and introduce a general mathematical hypothesis of the dynamics of a wide class of diseases, indicating the utility of ApEn to test this hypothesis. We indicate the relationship of ApEn to variability measures, the Fourier spectrum, and algorithms motivated by study of chaotic dynamics. We discuss further mathematical properties of ApEn, including the choice of input parameters, statistical issues, and modeling considerations, and we conclude with a section on caveats to ensure correct ApEn utilization.
Oxygen pressure distribution in the heart in vivo and evaluation of the ischemic "border zone"
Authors: Rumsey W. L. , Pawlowski M. , Lejavardi N. , Wilson D. F.
Published: December 2017

Quantitation of the oxygen pressure distribution in the heart provides an accurate definition of metabolically viable cells adjacent to ischemic injury. By injection of a phosphorescent oxygen probe into the blood of newborn piglets and illumination of the heart with monochromatic light, a series of images of the heart were collected with use of a gated intensified CCD camera. These sets of images were used to calculate two-dimensional maps of the oxygen pressure in the epicardial microvasculature. Occlusion of a distal arterial vessel resulted in a hypoxic area containing a central focus of near-zero oxygen pressure bordered by tissue with diminished but nonzero oxygen pressures. These border zones extended for several millimeters from the hypoxic core, with the oxygen pressures progressively increasing from the focus to the normoxic region. The maps of oxygen distribution obtained by phosphorescence imaging provide rapid and quantitative measure of the oxygen pressures in the beating heart in vivo. They accurately show the degree of oxygen deprivation and the extent of an ischemic border zone that may respond to treatment.
Role of nitroxidergic nerve in dog retinal arterioles in vivo and arteries in vitro
Authors: Toda N. , Kitamura Y. , Okamura T.
Published: December 2017

Functional role and anatomic location of nitroxidergic nerves were determined in dog retinal arteries and arterioles. Isolated retinal central arteries responded to nicotine with relaxations that were not influenced by atropine, timolol, or indomethacin and damage of the endothelium, but were abolished by hexamethonium, methylene blue, and oxyhemoglobin. The relaxation was abolished by NG-nitro-L-arginine (L-NNA), a nitric oxide (NO) synthase inhibitor, and was restored by L-arginine. Relaxations caused by NO were not affected by L-NNA. Transmural electrical stimulation at 5 Hz relaxed the strips; the relaxation was abolished by L-NNA and tetrodotoxin. In anesthetized dogs, intraarterial injections of nicotine dilated retinal arterioles in the fundus oculi. This effect was abolished by L-NNA and restored by L-arginine. Intravenous injections of L-NNA constricted retinal arterioles, the effect being prevented by hexamethonium. There were nerve bundles and fibers containing NO synthase immunoreactivity in the adventitia and media in the retinal artery. These findings are consistent with our hypothesis that NO liberated from vasodilator nerves acts as neurotransmitter in dog retinal arteries and arterioles, and the arteriolar muscle tone is regulated by vasodilator nerve activity in vivo.
Effects of LTD4 and its specific antagonist L-660,711 in isolated rat hearts with chronic myocardial infarction
Authors: Han H. , Tian R. , Neubauer S. , Gaudron P. , Hu K. , Ertl G.
Published: December 2017

We investigated the effects of leukotriene (LT) D4 and its novel potent and selective antagonist L-660,711 on isolated rat hearts with chronic myocardial infarction. The left coronary artery was ligated permanently or for 30 or 60 min and followed by reperfusion. Hearts were isolated and perfused in the Langendorff mode 4 days, 4 wk, or 8 wk after the operation. Dose-response curves for LTD4 (12-240 ng/min) on coronary flow were shifted to the left in rats with permanent coronary occlusion for 8 wk or with coronary occlusion for 30 or 60 min and reperfusion for 4 wk. In contrast, dose-response curves were unchanged in rats 4 days after myocardial infarction. L-660,711 shifted dose-response curves for LTD4 on coronary flow to the right in all groups. The negative inotropic and chronotropic effects of LTD4 could be markedly attenuated by L-660,711 in all groups. Our findings suggest that the effect of LTD4 is enhanced in rat hearts with chronic myocardial infarction. L-660,711 effectively antagonized the vasoconstrictor effect of exogenous LTD4.
Coenzyme Q10 enhances cardiac functional and metabolic recovery and reduces Ca2+ overload during postischemic reperfusion
Authors: Hano O. , Thompson-Gorman S. L. , Zweier J. L. , Lakatta E. G.
Published: December 2017

The effects of coenzyme Q10 (CoQ) were studied in isolated, isovolumic rat hearts during a 30-min period of global ischemia followed by 40 min of reperfusion. After reperfusion 1) the relative recovery of developed pressure (DP) was increased by CoQ (75 vs. 40% of the preischemic value for 20 microM CoQ and control hearts, respectively, P < 0.001); 2) diastolic pressure elevation was decreased by CoQ (20 vs. 50 mmHg in CoQ vs. control hearts, respectively, P < 0.001); and 3) recovery of high-energy phosphates and reduction of inorganic phosphate were approximately twofold greater in CoQ vs. control hearts (P < 0.001 for each parameter). The beneficial effects of CoQ were not observed when CoQ was added at the onset of reperfusion. The total free generation during reperfusion was not affected by CoQ. In unpaced hearts, in the presence of verapamil to prevent spontaneous beating, spontaneous Ca2+ oscillations were measured as scattered laser light intensity fluctuations (SLIF). The transient rise in SLIF in the postischemic reperfused myocardium, which previously has been shown to predict the extent of Ca2+ overload, was suppressed by CoQ (P < 0.001). These results suggest that while early CoQ treatment does not scavenge the primary burst of superoxide or hydroxy radical generation, which occurs on reperfusion, it markedly improves the functional recovery during reperfusion by enhancing the recovery of high-energy phosphates and preventing Ca2+ overload.
Decrease in vascular TxA2 receptors in a subgroup of rabbits unresponsive to a TxA2 mimetic
Authors: Buzzard C. J. , Pfister S. L. , Halushka P. V. , Campbell W. B.
Published: December 2017

In rabbit pulmonary artery, endothelium-dependent contractions to arachidonic acid and methacholine are mediated by thromboxane (Tx) A2. The TxA2 mimetics U-46619 and (1S-[1 alpha,2 beta(5Z),3 alpha(1E,3R*),4 alpha])-7-[3- [3-hydroxy-4-(4'-iodophenoxy)-1-butenyl]-7-oxabicyclo(2.2.1)hep tan-2-yl]- 5-heptenoic acid (I-BOP), norepinephrine, and endothelin produced endothelium-independent contractions. Arachidonic acid, methacholine, U-46619, and I-BOP failed to produce contractions in a subgroup of rabbits (25%). Nonresponder arteries contracted similarly to norepinephrine and endothelin as responder arteries. The affinity (Kd) and density (Bmax) of TxA2 receptors in crude pulmonary artery membranes were assessed via equilibrium binding studies using 125I-BOP. There was no difference in Kd between the two groups (0.49 +/- 0.17 vs. 0.32 +/- 0.14 nM, responder vs. nonresponder). There was a significant decrease in Bmax (123 +/- 21 vs. 28 +/- 11 fmol/mg protein, responder vs. nonresponder; P < 0.01) of receptors in the nonresponders. Nonresponder aortas also did not contract to U-46619 and exhibited a decrease in TxA2 receptors, indicating that the difference is not specific for the pulmonary artery. Nonresponder platelets aggregated to U-46619, suggesting that the platelet receptor is not altered. TxA2-receptor expression may be regulated in vivo. Nonresponder rabbits may provide a useful model for studying these receptors in vascular disease.
Effects of endogenous nitric oxide on pulmonary vascular tone in intact dogs
Authors: Leeman M. , de Beyl V. Z. , Delcroix M. , Naeije R.
Published: December 2017

The interaction between inspiratory fraction of O2 (FIO2) and endogenous nitric oxide (NO) regulation of pulmonary vascular tone was examined in intact anesthetized dogs. Stimulus (FIO2 of 1, 0.4, 0.21, 0.12, and 0.1)-response (changes in pulmonary artery pressure minus pulmonary artery occlusion pressure) curves were constructed with cardiac output kept constant (by opening a femoral arteriovenous bypass or inflating an inferior vena cava balloon catheter), before and after administration of compounds acting at different levels of the L-arginine-NO pathway, NG-nitro-L-arginine (L-NNA, 10 mg/kg iv, n = 16), a NO synthase inhibitor, and methylene blue (8 mg/kg iv, n = 16), a guanylate cyclase inhibitor. L-NNA and methylene blue did not influence pulmonary vascular tone in hyperoxic and in normoxic conditions, but they increased it during hypoxia, thus enhancing the vasopressor response to hypoxia (from 4.5 +/- 0.9 to 10.4 +/- 1.2 mmHg and from 4.2 +/- 0.8 to 9 +/- 1.5 mmHg, respectively, both P < 0.01). Hypoxic pulmonary vasoconstriction was augmented in dogs with a baseline hypoxic response (“responders”) and restored in dogs without hypoxic response (“nonresponders”). These results suggest that endogenous NO does not influence hyperoxic and normoxic pulmonary vascular tone, but that it inhibits hypoxic pulmonary vasoconstriction in intact anesthetized dogs.
Nitric oxide accounts for histamine-induced increases in macromolecular extravasation
Authors: Mayhan W. G.
Published: December 2017

The goal of this study was to determine the role of nitric oxide in histamine-induced increases in macromolecular extravasation in the hamster cheek pouch in vivo. We used intravital fluorescent microscopy and fluorescein isothiocyanate dextran (FITC-dextran; mol wt = 70,000 K) to examine extravasation from postcapillary venules in response to histamine before and after application of an enzymatic inhibitor of nitric oxide, NG-monomethyl-L-arginine (L-NMMA; 1.0 microM). Increases in extravasation of macromolecules were quantitated counting the number of venular leaky sites. Histamine (1.0 and 5.0 microM) increased the number of venular leaky sites from zero (basal conditions) to 11 +/- 1 and 21 +/- 2/0.11 cm2, respectively. Superfusion of L-NMMA (1.0 microM) and LY-83583 (1.0 microM) significantly decreased histamine-induced formation of venular leaky sites, whereas L-arginine (100 microM) potentiated histamine-induced formation of venular leaky sites. In contrast, superfusion of NG-monomethyl-D-arginine (1.0 microM) did not inhibit the formation of venular leaky sites in response to histamine. Thus the findings of the present study suggest that production of nitric oxide, and subsequent activation of guanylate cyclase, plays an important role in macromolecular efflux in vivo in response to histamine.
Impaired nitric oxide-dependent responses and their recovery in hypertensive pulmonary arteries of rats
Authors: Maruyama J. , Maruyama K.
Published: December 2017

To study the changes of endothelium-dependent and -independent relaxation in structurally remodeled pulmonary arteries with hypoxic pulmonary hypertension and their reversibility during recovery in room air, rats were exposed to hypobaric hypoxia (air at 380 mmHg) for 10 days and then allowed to recover in room air for 3, 14, 28, or 56 days. Relaxation by acetylcholine, sodium nitroprusside (SNP), and isoproterenol was depressed in large- and small-conduit pulmonary arterial rings from rats exposed to 10 days of hypoxia. The relaxant response to isoproterenol and SNP was normalized completely after 3 and 28 days of recovery, respectively. The relaxation by acetylcholine was still impaired at high concentrations after 56 days. A cyclooxygenase inhibitor, indomethacin, enhanced relaxation by acetylcholine of rings from experimental rats but not from control rats. Endothelium-denuded rings showed no difference in the response to acetylcholine between control and experimental rats. In conclusion, the impaired response to acetylcholine may be related to acetylcholine-induced, cyclooxygenase-dependent production of a vasoconstrictor by endothelial cells and to depressed smooth muscle response to nitric oxide (NO). During recovery, the NO-induced guanosine 3',5'-cyclic monophosphate-dependent dilation returned to normal. However, the release of cyclooxygenase-dependent production of a vasoconstrictor may persist even after 56 days of recovery.
Inhibition of tumor necrosis factor prevents myocardial dysfunction during burn shock
Authors: Giroir B. P. , Horton J. W. , White D. J. , McIntyre K. L. , Lin C. Q.
Published: December 2017

Tumor necrosis factor-alpha (TNF) is a pluripotent cytokine that mediates many of the hemodynamic manifestations of endotoxic shock. To determine whether TNF is responsible for postburn myocardial dysfunction, we compared cardiac function (Langendorff preparation) in 49 guinea pigs 18 h after thermal injury. Group 1 (n = 15) was sham burned; all remaining animals received a 43% surface area burn under anesthesia. Group 2 (n = 15) received lactated Ringer solution (LR, 4 ml.kg-1.%burn-1). Group 3 (n = 9) received LR and drug vehicle. Group 4 (n = 10) received LR plus 1 mg of TNF inhibitor consisting of the human p80 TNF receptor linked to the Fc portion of human immunoglobulin G1, which was shown to specifically bind and neutralize TNF secreted by guinea pig peritoneal macrophages in vitro. Burn injury caused a significant fall in left ventricular pressure (LVP, from 86 +/- 2 to 62 +/- 3 mmHg, P < 0.05) and maximal rate of LVP rise (+) and fall (-) (+/- dP/dtmax) [from 1,365 +/- 42 to 1,109 +/- 44 mmHg/s (P < 0.05) and from 1,184 +/- 31 to 881 +/- 40 mmHg/s (P < 0.05), respectively], a decrease in time to peak systolic LVP (from 111 +/- 2 to 102 +/- 2 ms, P < 0.05), and a decrease in time to +dP/dtmax (from 57 +/- 1 to 48 +/- 1 ms, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of respiratory interval on vagal modulation of heart rate
Authors: Hayano J. , Mukai S. , Sakakibara M. , Okada A. , Takata K. , Fujinami T.
Published: December 2017

To determine whether paced breathing (PB) and respiratory interval of PB modify the relationship between spectral components of heart rate variability (HRV) and cardiac vagal tone, we studied seven healthy young males under the condition of beta-adrenergic blockade by intravenous propranolol (0.2 mg/kg). Compared with spontaneous breathing, PB at the same respiratory interval as that of individual spontaneous breathing showed no significant effect on the amplitude of the high-frequency (HF) component or the mean R-R interval in either the supine or tilt position, whereas the PB decreased the amplitude of the low-frequency (LF; 0.04–0.15 Hz) component in both positions (P = 0.004 and 0.042, respectively). When the respiratory interval was increased from 3 to 6 s, the HF amplitude showed a progressive increase in both positions (P = 0.001 and 0.035, respectively), while the LF amplitude and mean R-R interval remained unchanged. These results indicate that the effects of PB and respiratory interval on the spectral components of HRV are not mediated by the changes in mean cardiac vagal tone and support the hypothesis that increased respiratory interval amplifies the respiratory-related vagal modulation of heart rate.
Effects of R-56865 on transient inward current, Na+-Ca2+ exchange, and Ca2+ release from SR in cardiac myocytes
Authors: Ichikawa H. , Hearse D. J. , Coetzee W. A.
Published: December 2017

Pages H511–H520: H. Ichikawa, D. J. Hearse, and W. A. Coetzee. “Effects of R-56865 on transient inward current, Na+-Ca2+ exchange, and Ca2+ release from SR in cardiac myocytes.” The concentration of R-56865 should be 1 μM and not 1 mM as stated in the paper.
Intracellular signal transduction systems do not regulate Na channel in frog ventricular cells
Authors: Sumii K. , Munemori M. , Miyoshi H. , Seyama I.
Published: December 2017

The regulation of sodium channel activity through intracellular signal transduction systems was studied on isolated frog ventricular cells using a whole cell patch-clamp technique. Special care was exercised in evaluating the stability of the voltage-clamp condition by observing shifts in the steady-state inactivation curve (h infinity curve) and changes in series resistance. We applied the following reagents: isoproterenol (Iso; 0.1–10 microM) and forskolin (Fsk; 0.1–10 microM) to activate protein kinase A. 1-Oleoyl-2-acetyl-sn-glycerol (40 microM) and 12-O-tetradecanoylphorbol-13-acetate (80-800 nM) were used to activate protein kinase C, and phenylephrine (0.1–10 microM), dopamine (0.1-10 microM), and histamine (10 microM) were used to stimulate alpha-adrenergic, dopaminergic, and histaminergic receptors, respectively. The current-voltage relationship and the h infinity curve for the sodium channel remained unchanged regardless of the application of these reagents. Iso and Fsk did not affect the sodium current but substantially increased the calcium current, suggesting that the intracellular signal transduction systems remained intact. Therefore, it is concluded that sodium channel in frog ventricular cells is not regulated by intracellular signal transduction systems.
Role of EDRF/NO in parasympathetic coronary vasodilation following carotid chemoreflex activation in conscious dogs
Authors: Shen W. , Ochoa M. , Xu X. , Wang J. , Hintze T. H.
Published: December 2017

The role of endothelium-derived relaxing factor (EDRF) in parasympathetic coronary vasodilation following carotid chemoreflex activation induced by nicotine in conscious dogs and stimulation of the vagus nerve in anesthetized dogs was studied. Injection of nicotine (11 +/- 4 micrograms) into the carotid artery increased coronary blood flow (CBF) by 126 +/- 16% from 28 +/- 3 ml/min and reduced late diastolic coronary resistance (LDCR) by 43 +/- 4% from 3.58 +/- 0.52 mmHg.ml-1.min, accompanied by a significant increase in mean arterial pressure and a decrease in heart rate (all P < 0.01). Pacing and propranolol did not change the coronary vascular response to chemoreflex activation. There were still increases in CBF by 113 +/- 17% from 29 +/- 3 ml/min and decreases in LDCR by 41 +/- 5% from 3.13 +/- 0.52 mmHg.ml-1.min (all P < 0.01). After infusion of N omega-nitro-L-arginine (L-NNA) (30 mg/kg), the increase in CBF following chemoreflex activation was only 23 +/- 3% from 37 +/- 3 ml/min, and the fall in LDCR was 19 +/- 3% from 3.09 +/- 0.51 mmHg.ml-1.min. Stimulation of the vagus nerve showed a relationship between stimulation frequency and coronary vasodilation that was significantly inhibited by L-NNA. Thus EDRF plays an important role in mediating parasympathetic coronary vasodilation during chemoreflex activation and perhaps during many reflexes that cause vagal cholinergic vasodilation in the heart.
KCl depolarization increases Ca2+ sensitivity of contractile elements in coronary arterial smooth muscle
Authors: Yanagisawa T. , Okada Y.
Published: December 2017

The effects of KCl depolarization on the Ca2+ sensitivity of contractile elements were studied using simultaneous measurement of intracellular Ca2+ concentration ([Ca2+]i) and force of contraction in isolated canine coronary artery. Perfusion with 90 mM KCl-2.5 mM CaCl2 physiological salt solution (PSS) (90K-2.5Ca) increased [Ca2+]i and elicited a contraction. The repolarization produced by 5 mM KCl-2.5 mM CaCl2 PSS (5K-2.5Ca) or the removal of extracellular Ca2+ ([Ca2+]o) and addition of 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA; 90K-0Ca) induced decreases in [Ca2+]i and relaxations. The relaxation induced by 90K-0Ca was slower than that induced by 5K-2.5Ca without significant difference in the decrease in [Ca2+]i, suggesting that the Ca2+ sensitivity may be increased in depolarized muscles in 90K-0Ca. The reduction of extracellular Na+ concentration did not slow down the relaxation. The [Ca2+]i-force relation curve in 30K-0Ca was between that in 5K-0Ca and that in 90K-0Ca. The [Ca2+]i-force relationship curve obtained by changing the extracellular K+ concentration stepwise in 2.5 mM CaCl2 PSS was located to the right of that by changing [Ca2+]o in 90 mM KCl PSS. These results indicate that KCl depolarization increases the Ca2+ sensitivity of contractile elements. There may be a signal transduction system for the sarcolemma to regulate Ca2+ sensitivity of contractile elements by the level of membrane potential.
Prostaglandin I2 mediates contraction and relaxation of vascular smooth muscle
Authors: Williams S. P. , Dorn G. W. , Rapoport R. M.
Published: December 2017

Prostaglandin (PG) I2 elicits a biphasic concentration-response curve in rat aorta: lower concentrations elicit relaxation, whereas at higher concentrations, the relaxation is reversed. The purpose of this study was to investigate 1) the nature of the receptors that mediate these effects and 2) whether the relaxant efficacy of PGI2 is decreased at higher PGI2 concentrations by PGI2-induced contraction. PGI2 (1 microM), the stable PGI2 analogue carbacyclin (1 microM), and PGE1 (3 microM) induced maximal relaxations of 55, 40, and 63%, respectively, of norepinephrine-contracted aorta, whereas higher concentrations of PGI2, carbacyclin, and PGE1 reversed the relaxation. The thromboxane (Tx) A2-PGH2 receptor antagonist, SQ-29548, abolished the reversal of the PGI2-, carbacyclin-, and PGE1-induced relaxation, and maximal relaxations to PGI2, carbacyclin, and PGE1 increased to 73, 85, and 89% of the norepinephrine contraction, respectively, with 50% effective concentrations of 0.16, 0.43, and 0.83 microM, respectively. PGE2 and PGD2 did not induce relaxation in the presence or absence of SQ-29548. PGI2 and carbacyclin displaced the TxA2-PGH2 receptor ligand 1S-[1 alpha,2 beta(5Z),3 alpha(1E,3S),4 alpha]-7-(3-[3-hydroxy-4-(p- [125I]iodophenoxy)-1-butenyl]7-oxabicyclo[2.2.1]hept-2-yl]-5- heptenoic acid from cultured rat aorta smooth muscle cells with concentrations of competing ligand that displaced 50% of the specifically bound radioligand from its binding site of 6.0 and 2.3 microM, respectively. These results suggest that 1) PGI2 induces relaxation through a PGI2-PGE1 receptor, and 2) higher concentrations of PGI2 act at the TxA2-PGH2 receptor to decrease PGI2-induced relaxation.
Protein kinase inhibitors reduce SR Ca transport in permeabilized cardiac myocytes
Authors: Mattiazzi A. , Hove-Madsen L. , Bers D. M.
Published: December 2017

Phosphorylation of the sarcoplasmic reticulum (SR) protein phospholamban by adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase (PKA) and Ca-calmodulin-dependent protein kinase (CaM-KII) stimulates Ca-adenosinetriphosphatase (ATPase) activity and SR Ca transport, but the role of CaM-KII-dependent phosphorylation is not well defined. We studied the PKA- and CaM-KII-dependent regulation of SR Ca transport in digitonin-permeabilized rabbit ventricular myocytes. SR Ca uptake and free Ca concentration were measured on line with indo 1 and Ca electrodes in the presence of 20 microM ruthenium red and 10 mM oxalate. neither N5,2'-w-dibutyryl-cAMP (up to 500 microM) nor the nonhydrolyzable cAMP agonist adenosine 3'5'-cyclic monophosphorothioate sodium salt (Sp-cAMP[S]; up to 275 microM) affected the maximum uptake rate (Vmax) or the dissociation constant (Kd) for Ca uptake. However, the PKA inhibitor H-89 significantly increased Kd (e.g., from 307 +/- 67 to 826 +/- 62 nM Ca at 40-65 microM H-89) without significantly affecting Vmax. Both CaM-KII inhibitors, KN-62 (60 microM) and a CaM-KII inhibitory peptide (10 microM), significantly decreased Vmax from 11.95 +/- 0.5 to 9.48 +/- 0.6 nmol.mg-1.min-1 and from 10.95 +/- 1.72 to 7.37 +/- 0.94 nmol.mg-1.min-1, respectively, without consistently changing Kd. The effects of H-89 on Kd and of KN-62 on Vmax were prevented by a monoclonal antibody to phospholamban 2D12 (consistent with the antibody removing the inhibitory effect of phospholamban on the SR Ca-ATPase).(ABSTRACT TRUNCATED AT 250 WORDS)
L-NNA decreases cortical hyperemia and brain cGMP levels following CO2 inhalation in Sprague-Dawley rats
Authors: Irikura K. , Maynard K. I. , Lee W. S. , Moskowitz M. A.
Published: December 2017

The role of nitric oxide (NO) in the response to 5% CO2 inhalation was investigated by measuring 1) regional cerebral blood flow (rCBF) by laser-Doppler flowmetry and pial vessel diameter through a closed cranial window after topical NG-nitro-L-arginine (L-NNA, 1 mM), and 2) the time-dependent changes in brain guanosine 3',5'-cyclic monophosphate (cGMP) levels after L-NNA (10 mg/kg ip). When L-NNA (but not NG-nitro-D-arginine) was applied topically for 30 or 60 min, the response to hypercapnia was significantly attenuated. A correlation was found between inhibition of brain NO synthase (NOS) activity and the rCBF response (r = 0.77; P < 0.01). However, L-NNA applied 15 min before hypercapnia did not attenuate the increase in rCBF but did attenuate the dilation to topical acetylcholine. Inhalation of CO2 (5%) elevated brain cGMP levels by 20–25%, and L-NNA reduced this response. These data from the rat suggest that 1) a product of NOS activity is associated with hypercapnic hyperemia and the attendant increase in brain cGMP levels, and 2) hypercapnic blood flow changes may not be dependent on endothelial NOS activity within pial vessels.
Effects of venous pressure on coronary circulation and intramyocardial fluid mechanics
Authors: Izrailtyan I. , Frasch H. F. , Kresh J. Y.
Published: December 2017

This investigation examined the interaction between right heart pressure (RHP), coronary perfusion pressure (CPP), intramyocardial tissue pressure (IMP), and coronary flow mechanics, including partitioning of coronary effluent in the isolated Krebs-Henseleit perfused rabbit heart. The major new finding was a parallel shift in the IMP-inflow relationship to a higher tissue pressure level in response to an increase in RHP. Accompanying the rise in RHP from 0 to 15 and 25 mmHg, IMP at zero coronary inflow in the beating (and arrested) heart increased from 5.8 +/- 1.0 (7.7 +/- 1.2) to 16.3 +/- 1.2 (17.9 +/- 1.3) and 28.6 +/- 1.7 (26.4 +/- 2.0) mmHg, respectively. A concomitant parallel shift in the CPP-inflow relation to higher pressures was consistently observed. The fraction of total coronary flow drained by the right heart was not constant. A higher partition of coronary outflow to the left heart (7.8 +/- 3.8, 34.3 +/- 3.0, and 47.9 +/- 4.3%, respectively) accompanied the increase in RHP. Intramyocardial partitioning of coronary outflow pathways mediates the effects of venous pressure modulation on coronary circulation. The interaction between coronary venous pressure and the extravascular environment modifies the effective back pressure to arterial inflow.
Modification of the gating of the cardiac sarcoplasmic reticulum Ca(2+)-release channel by H2O2 and dithiothreitol
Authors: Boraso A. , Williams A. J.
Published: December 2017

The effect of hydrogen peroxide (H2O2) on the sheep cardiac sarcoplasmic reticulum (SR) Ca(2+)-release channel has been investigated under voltage-clamp conditions after incorporation of native membrane vesicles into planar phospholipid bilayers. In the presence of micromolar activating calcium concentrations on the cytosolic side of the membrane, H2O2 (3-5 mM) increased open probability of the channels. H2O2 did not affect the conductance of the channel or the response to activating compounds, such as ATP and caffeine. H2O2 did not alter the inhibitory response to magnesium or the modification of channels by ryanodine. At subactivating calcium concentrations (approximately 45 pM) on the cytosolic side of the membrane, 5 mM H2O2 was still able to open the channel. Analysis of single-channel open and closed lifetimes suggested that H2O2 had a direct effect on the gating mechanism of the channel. Open probability of the SR Ca(2+)-release channel is reduced by millimolar concentrations of dithiothreitol, a sulfhydryl-protecting compound, in a concentration-dependent manner. In conclusion, it is probable that H2O2 activates the SR Ca(2+)-release channel via an oxidation of cysteine thiol groups in the channel protein.
Nitric oxide selectively amplifies FGF-2-induced mitogenesis in primary rat aortic smooth muscle cells
Authors: Hassid A. , Arabshahi H. , Bourcier T. , Dhaunsi G. S. , Matthews C.
Published: December 2017

Fibroblast growth factor is present in blood vessels and is thought to play an important role in promoting vascular cell proliferation in vivo. In the current study, we show that three agents that activate the guanosine 3',5'-cyclic monophosphate (cGMP) system, including the nitric oxide-generating agents S-nitroso-N-acetylpenicillamine (SNAP) and 3-morpholinosydnonimine-N-ethylcarbamide (SIN-1) as well as the stable cGMP analogue 8-bromo-cGMP, increased fibroblast growth factor-2 (FGF-2; basic fibroblast growth factor)-induced [3H]thymidine incorporation by severalfold in primary cultures of rat aortic smooth muscle cells. SNAP increased the efficacy, but not the potency, of FGF-2. The stimulatory effect of SNAP was selective for FGF-2-induced mitogenesis as shown by the lack of a significant effect on [3H]thymidine incorporation induced by several other growth factors. Consistent with thymidine incorporation experiments, SNAP amplified the increase of the cellular DNA content induced by FGF-2 as well as the proliferation of cells. A selective inhibitor of cGMP phosphodiesterases, zaprinast, potentiated the comitogenic effect of SNAP and its ability to increase cGMP levels, supporting the involvement of cGMP as second messenger. Consistent with previous results, and opposite to that found in primary and early subculture, SNAP decreased mitogen-induced [3H]thymidine incorporation in cells in later subculture. Because macrophage- and vascular smooth muscle-derived nitric oxide is likely to be present in relatively large concentrations after vascular injury, we speculate that endogenous nitric oxide may amplify the activity of FGF-2 in vivo.
Effects of aging on quantitative structural properties of coronary vasculature and microvasculature in rats
Authors: Anversa P. , Li P. , Sonnenblick E. H. , Olivetti G.
Published: December 2017

To determine whether the alterations in coronary vascular resistance with aging have a structural basis, the quantitative properties of the intramural branches of the coronary circulation and capillary network were measured in Fischer 344 rats at 4, 12, 20, and 29 mo. Physiological measurements demonstrated that a severe impairment in cardiac pump function developed with age, leading to the occurrence of ventricular failure at 29 mo. Morphometrically, the length densities of resistance vessels from 6 to 20 microns in luminal diameter markedly decreased at 12 mo, and this change persisted at 20 and 29 mo. This phenomenon affected the inner, middle, and outer layers of the left ventricular wall. In contrast, capillary luminal volume percentage, capillary numerical density, and average diffusion distance for oxygen in the left and right myocardium were altered only at 20 mo, whereas values comparable to those at 4 mo were found at 12 and 29 mo. The preservation of these capillary characteristics in the heart was due to a significant amount of capillary proliferation. In conclusion, aging effects lead to rarefaction of coronary arterioles in the myocardium, which may impair coronary resistance and reserve without altering the capillary microvasculature and the oxygenation potential of the old and senescent heart.
TEA inhibits ACh-induced EDRF release: endothelial Ca(2+)-dependent K+ channels contribute to vascular tone
Authors: Demirel E. , Rusko J. , Laskey R. E. , Adams D. J. , van Breemen C.
Published: December 2017

The effects of K(+)-channel blockers on the acetylcholine (ACh)-induced relaxation of vascular smooth muscle, intracellular free Ca2+ concentration ([Ca2+]i) elevation, and ACh-evoked outward K+ current of endothelial cells of rabbit aorta were studied using bioassay, spectrofluorimetry, and patch-clamp techniques, respectively. In bioassay experiments, ACh caused relaxation of endothelium-denuded aortic rings in a concentration-dependent manner when perfused through an endothelium-intact donor segment of aorta but not when perfused directly onto the recipient aortic ring. ACh-induced relaxation was inhibited by perfusion of tetraethylammonium ions (TEA; 5 mM) through the donor but not by perfusion directly onto the recipient segment. Glibenclamide had no effect on ACh-induced relaxation of the bioassay ring in either situation. ACh increased [Ca2+]i at the endothelial surface of aortic strips but not at the adventitial surface. TEA inhibited ACh-induced [Ca2+]i elevation, whereas glibenclamide had no effect. In patch-clamp experiments with freshly isolated endothelial cells, ACh evoked a biphasic outward current which was completely abolished by TEA (3 mM). It is concluded that Ca(2+)-dependent K+ channels are important for increasing [Ca2+]i during agonist stimulation and consequently for the synthesis/release of endothelium-derived relaxing factors (EDRFs). Furthermore, endothelial ATP-sensitive K+ channels do not contribute to ACh-induced relaxation or evoke an increase in endothelial [Ca2+]i of rabbit thoracic aorta.
Influence of acute alterations in cycle length on ventricular function in chick embryos
Authors: Casillas C. B. , Tinney J. P. , Keller B. B.
Published: December 2017

Heart rate (HR), developed pressure, and stroke volume (SV) increase dramatically during cardiac morphogenesis. During acute changes in cycle length (CL), the chick embryo maintains cardiac output by a compensatory change in SV. We determined embryonic pressure-volume relations during alterations in CL in the stage 21 while Leghorn chick embryo to quantitate the relationship between CL and cardiac time intervals, ventricular preload, and ventricular function. CL was transiently altered to 73-191% of initial baseline CL with a 1-mm randomly preheated or cooled metal probe applied to the sinus venosus. Isometric relaxation, diastolic filling, and systolic ejection times varied linearly with CL, whereas isometric contraction times were similar. SV varied linearly with CL, ejection time, and end-diastolic volume. In contrast to the mature heart, the relationship between SV and end-systolic pressure was inverse. Embryonic ventricular preload was influenced acutely by diastolic filling time, and cardiac output was optimized during changes in CL by ventricular-vascular interactions that matched SV inversely to HR.
Ca2+ handling and myofibrillar Ca2+ sensitivity in ferret cardiac myocytes with pressure-overload hypertrophy
Authors: Wang J. , Flemal K. , Qiu Z. , Ablin L. , Grossman W. , Morgan J. P.
Published: December 2017

Experiments were performed in aequorin-loaded left ventricular myocytes isolated from hypertrophied hearts and age-matched controls. Five to six months after postvalvular aortic banding, left ventricular hypertrophy was present, as indicated by a 97% (P < 0.001) increase in the left ventricular weight-to-body weight ratio and a 24% (P < 0.001) increase in cell width. In comparison with controls, the hypertrophied myocytes demonstrated that 1) contraction duration was prolonged by 37% (P < 0.001) and was associated with a 44% (P < 0.001) prolongation of the intracellular Ca2+ transient; 2) peak systolic shortening was decreased by 31% (P < 0.001) and was associated with a 21% (P < 0.001) decrease in peak systolic intracellular Ca2+ concentration; 3) both the peak systolic intracellular Ca2+ concentration-to-peak shortening relationship and the intracellular Ca2+ concentration-to-cell shortening relationship at the time of the peak twitch were shifted downward, suggesting a decrease in myofilament Ca2+ responsiveness; and 4) isoproterenol (5 x 10(-8) M) produced equal increases in the peak systolic intracellular Ca2+ of control and hypertrophied myocytes (88 vs. 90%; P > 0.05) in contrast to much smaller increases in the peak cell shortening (170 vs. 73%; P < 0.02) of the hypertrophied myocytes, suggesting a decrease in myofilament Ca2+ responsiveness. These data demonstrate that the hypertrophy-related abnormalities in intracellular Ca2+ handling and mechanical function, previously reported in aequorin-loaded multicellular muscle preparations, are present in isolated myocytes, arguing against changes in the interstitium as essential causative factors.
Adenosine output from dog gracilis muscle during systemic hypercapnia and/or amiloride-SITS infusion
Authors: Mo F. M. , Ballard H. J.
Published: December 2017

The influence of acidosis on adenosine output from the isolated constant-flow-perfused gracilis muscle was studied in anesthetized dogs. Depression of intracellular pH (pHi) by supplementation of the inspired air with 10% CO2-90% O2 increased arterial PCO2 from 34.2 +/- 1.0 to 53.5 +/- 1.9 mmHg, arterial PO2 from 138.3 +/- 3.9 to 256.6 +/- 17.6 mmHg, and venoarterial adenosine concentration from 14 +/- 15 to 47 +/- 19 nM. Twitch contractions of the muscle at 2 Hz increased venoarterial adenosine concentration to 165 +/- 63 and 204 +/- 62 nM in normocapnia and hypercapnia, respectively. Venoarterial lactate concentration increased from 0.42 +/- 0.07 to 0.90 +/- 0.15 mM during normocapnic contractions but remained unchanged during hypercapnic contractions (0.42 +/- 0.11 mM). Depression of pHi by infusion of amiloride and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid increased venoarterial adenosine concentration from -2 +/- 27 to 124 +/- 48 nM in normocapnia and from 16 +/- 24 to 236 +/- 119 nM in hypercapnia. These results indicate that adenosine output from red oxidative skeletal muscle was stimulated by procedures that depress pHi.
Physiological assessment of augmented vascularity induced by VEGF in ischemic rabbit hindlimb
Authors: Bauters C. , Asahara T. , Zheng L. P. , Takeshita S. , Bunting S. , Ferrara N. , Symes J. F. , Isner J. M.
Published: December 2017

This study was designed to assess the physiological consequences of augmented vascularity induced by administration of vascular endothelial growth factor (VEGF), an endothelial cell-specific mitogen, in a rabbit model of hindlimb ischemia. Ten days after excision of the common and superficial femoral arteries from one hindlimb of 24 New Zealand White rabbits, VEGF (n = 15) or saline (control; n = 9) was selectively injected into the ipsilateral internal iliac artery. Limb perfusion was evaluated immediately pre-VEGF (baseline) and again at days 10 and 30. A Doppler guide wire was advanced to the internal iliac artery to record flow velocity at rest and at maximum flow velocity provoked by intra-arterial injection of papaverine. At baseline and at day 10, no differences in flow parameters were observed between the control and the VEGF-treated animals. By day 30, however, flow at rest (P < 0.05), maximum flow velocity (P < 0.001), and maximum blood flow (P < 0.001) were all significantly higher in the VEGF-treated group. These physiological findings complement previous-anatomic studies by providing evidence that a single intra-arterial bolus of VEGF augments flow, particularly maximum flow, in the rabbit ischemic hindlimb. These data thus support the notion that VEGF administration represents a potential treatment strategy for certain patients with lower extremity ischemia.