bluuebunny/crossref_metadata_2025 huggingface dataset:
Neurons in area postrema mediate vasopressin-induced enhancement of the baroreflex
Authors: Cox B. F. , Hay M. , Bishop V. S.
Published: December 2017

Intravenous infusion of arginine vasopressin (AVP) has been shown to enhance baroreflex sensitivity, and this enhancement is dependent on the integrity of the area postrema. However, previous studies did not differentiate a role for cell bodies in the area postrema vs. the dense network of fibers located in and around the lateral and ventral margins of this circumventricular organ. In the present study, baroreflex function was assessed in conscious rabbits by examining heart rate after ramp infusions of phenylephrine (PE) and AVP. The subsequent day, the excitotoxin kainic acid was injected (30 nl initially, with five 15-nl supplemental injections of a 1 ng/nl solution over 1 h) into the area postrema, thus selectively destroying cell bodies. After an 8-day recovery period, baroreflex function was again assessed. The bradycardic response to graded infusion of PE (slope = -2.29 +/- 0.30) was not significantly different after selective lesions of area postrema neurons (slope = -1.88 +/- 0.49). In contrast, the previously enhanced bradycardic response to infusion of AVP (slope = -5.76 +/- 1.02) was significantly attenuated (slope = -2.31 +/- 0.21) to levels similar to that seen with infusion of PE. Thus selective chemical lesions of area postrema neurons block vasopressin-induced enhancement of the baroreflex.
Cholinergic regulation of resting coronary blood flow in domestic swine
Authors: Cowan C. L. , McKenzie J. E.
Published: December 2017

Cholinergic vasoconstriction in vivo and the influence of resting cholinergic activity on basal coronary tone were investigated by measuring coronary blood flow, cardiac function, and blood gases during either acetylcholine injection, muscarinic receptor blockade, or vagal ligation, in open-chest chloralose-urethan-anesthetized swine. Intracoronary injections of acetylcholine (0.5-3.0 micrograms) caused significant (P less than 0.05) dose-dependent reductions in coronary blood flow (19.0–75.5%) and conductance (14.3–78.2%). Atropine (200 micrograms) completely blocked these responses. Cholinergic mediation of basal coronary tone was initially evaluated by determining the effects of muscarinic blockade with intracoronary injection of atropine (200 micrograms). Intracoronary injection of atropine had no significant effects on coronary blood flow or conductance. Finally, to ensure that parasympathetically released acetylcholine was not overcoming the muscarinic blockade, vagal ligation was performed during pacing. Neither coronary blood flow nor conductance was significantly altered by vagal ligation. The present studies demonstrate that acetylcholine induces a muscarinic vasoconstriction of coronary arteries in the domestic swine. However, these studies do not support a role for parasympathetic mediation of basal coronary vascular tone.
Subcellular distribution of peroxidized lipids in myocardial reperfusion injury
Authors: Romaschin A. D. , Wilson G. J. , Thomas U. , Feitler D. A. , Tumiati L. , Mickle D. A.
Published: December 2017

Previous studies in our laboratory have demonstrated the peroxidation of myocardial phospholipid in a canine model of reversible global normothermic ischemia and reperfusion while on cardiopulmonary bypass. The present study examines the distribution of phospholipid peroxidation products in three major cellular organelle fractions of myocardium prepared by established centrifugal fractionation procedures (sarcolemma, sarcoplasmic reticulum, and mitochondria). These organelles were isolated from control (nonischemic) and ischemic-reperfused myocardium harvested during early reperfusion (5 min), when previous studies indicated maximal peroxidative injury in whole myocardial biopsies. Utilizing a more rapid analytic procedure for measuring phospholipid containing the conjugated diene chromophore in the polyunsaturated fatty acyl substituents, we were able to establish the fidelity of this procedure by comparing the results obtained with it to the previous more laborious analytic procedure (involving phospholipid hydrolysis with phospholipase A2 and subsequent derivatization for high-pressure liquid chromatography followed by gas chromatographic-mass spectrometric analysis). Analysis of phospholipid extracts from organelle fractions for evidence of peroxidative conjugated diene formation revealed that sarcolemmal membranes had the highest content of oxidized phospholipid containing the conjugated diene chromophore (mean 2.2 +/- 1.2 nmol phospholipid-conjugated diene/mumol phospholipid phosphorus, P less than 0.02 compared with control). Both sarcoplasmic reticulum and mitochondrial membranes were also peroxidized but to a much smaller extent (mean 0.4 +/- 0.2 and 0.3 +/- 0.25 nmol phospholipid conjugated diene/mumol phospholipid phosphorus).
U74500A inhibition of oxidant-mediated lung injury
Authors: Haynes J. , Seibert A. , Bass J. B. , Taylor A. E.
Published: December 2017

Toxic oxygen species are thought to play a primary role in the pathophysiological mechanisms responsible for a diverse group of lung diseases. In this study, isolated perfused rat lungs were subjected to oxidant injury induced by ischemia-reperfusion (IR) and t-butyl hydroperoxide (t-buOOH) challenge. Both forms of injury caused large increases in capillary permeability as assessed by the capillary filtration coefficient (Kfc). IR and t-buOOH challenge caused increases in the Kfc of 0.95 +/- 0.22 and 0.30 +/- 0.06 ml.min-1.cmH2O-1.100 g lung tissue-1, respectively. U74500A, a potent inhibitor of iron-mediated lipid peroxidation, significantly attenuated the endothelial damage seen in both forms of injury. In lungs pretreated with U74500A, the Kfc increased 0.01 +/- 0.02 and 0.11 +/- 0.03 ml.min-1.cmH2O-1.100 g lung tissue-1 following IR and t-buOOH challenge, respectively. In lungs pretreated with the iron binding protein transferrin the Kfc increased 0.31 +/- 0.11 and 0.19 +/- 0.03 ml.min-1.cmH2O-1.100 g lung tissue-1 following IR and t-buOOH challenge, respectively. In these studies, transferrin significantly attenuated permeability in the IR group only. However, the attenuation of injury in IR due to U74500A was significantly greater (P less than 0.05) than the attenuation provided by transferrin. Both forms of injury also caused small but statistically significant increases in pulmonary artery pressure. These results suggest that the increase in capillary permeability seen after IR and t-buOOH is in part mediated by iron-dependent mechanisms.
Evidence for increased myofilament Ca2+ sensitivity in norepinephrine-activated vascular smooth muscle
Authors: Nishimura J. , Khalil R. A. , Drenth J. P. , van Breemen C.
Published: December 2017

The agonist-induced change in Ca2+ sensitivity of smooth muscle myofilaments was investigated in intact and permeabilized vascular preparations isolated from the rat and the rabbit. In intact rat mesenteric artery, membrane depolarization by 80 mM K+ solution or alpha-adrenergic stimulation by norepinephrine (NE) increased tension monotonically with increasing extracellular Ca2+ concentration ([Ca2+]e). The [Ca2+]e-tension curve generated during activation by NE was located to the left of that during activation by high K+. The protein kinase C (PKC) activator 12-O-tetradecanoylphorbol-13-acetate (TPA) shifted the high K+ [Ca2+]e-tension curve to the left but did not affect the NE curve. In rat mesenteric artery permeabilized by alpha-toxin, tension was measured while the intracellular free Ca2+ concentration ([Ca2+]i) was controlled using 2 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N'N'-tetraacetic acid and Ca2+ buffer solutions. The alpha-toxin-permeabilized fibers developed tension as a function of Ca2+ concentration. TPA and guanosine 5'-[gamma-thio]triphosphate (GTP gamma S, a nonhydrolyzable GTP analogue) significantly shifted the pCa-tension curve to the left. In intact rabbit inferior vena cava, tension was recorded simultaneously with [Ca2+]i as measured by fura-2. TPA caused a gradual increase in tension without change in [Ca2+]i. In rabbit mesenteric artery permeabilized by alpha-toxin, the tissue still responded to NE, indicating that alpha-adrenergic receptors remained intact. The response to NE was augmented by GTP and inhibited by guanosine 5'-[beta-thio]diphosphate (GDP beta S, a nonhydrolyzable GDP analogue) suggesting that a G protein is coupled with the alpha-adrenergic receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
Reperfusion-induced leukocyte infiltration: role of elastase
Authors: Zimmerman B. J. , Granger D. N.
Published: December 2017

Polymorphonuclear leukocytes are known to accumulate in tissues subjected to ischemia and reperfusion. Studies on endothelial cell monolayers suggest that limited release of elastase plays an important role, via basement membrane degradation, in the leukocyte diapedesis and extravasation elicited by proinflammatory mediators. Thus the objective of this study was to define the role of elastase in the leukocyte infiltration associated with reperfusion of the ischemic bowel. In one series of experiments the cat small intestine was subjected to 3 h of ischemia (blood flow reduced to 20% of base line) and 1 h of reperfusion. Neutrophil accumulation was quantified by measurement of tissue myeloperoxidase activity in mucosal biopsies obtained during base-line, ischemic, and reperfusion periods. Pretreatment with either of the elastase inhibitors Eglin C and L658,758 significantly attenuated the neutrophil infiltration induced by reperfusion but not by ischemia per se. In another series of experiments, leukocyte adherence and extravasation were monitored in cat mesenteric venules subjected to 1 h of ischemia and reperfusion. Pretreatment with L658,758 significantly attenuated the increased rates of leukocyte adherence and extravasation induced by reperfusion, with a proportionately greater reduction in leukocyte extravasation rate. These results indicate that elastase release is an important factor in reperfusion-induced neutrophil infiltration.
Rest decay of calcium transients and contractility in feline ventricular myocytes
Authors: DuBell W. H. , Houser S. R.
Published: December 2017

To define the respective contributions of sarcoplasmic reticulum Ca2+ release and action potential-dependent Ca2+ influx to the activator Ca2+, rest decay of the cytosolic free Ca2+ (Ca2+i) transient and contractility was measured in feline ventricular myocytes loaded with the Ca2(+)-sensitive fluorescent dye indo-1. Myocytes were stimulated to a steady state and then rested for periods ranging from 2 to 120 s. Rest decay was assayed with both resumption of stimulation and rapid extracellular applications of caffeine. The protocol was then repeated after exposure to ryanodine. Ryanodine changed the Ca2+i transients during steady-state stimulation from large, rapidly rising transients starting near the resting Ca2+i level to small, slowly rising Ca2+i transients superimposed on an elevated diastolic Ca2+i. Under control conditions the stimulation- and caffeine-induced Ca2+i transients exhibited slow monotonic rest decay with similar time constants of decay (180 and 202 s, respectively, from a representative cell). After ryanodine, the rest decay of stimulation-induced Ca2+i transients was seemingly no different. However, no Ca2+i transient could be elicited by caffeine after 15 s of rest. These results suggest that 1) under normal conditions the primary source of activator Ca2+ is the sarcoplasmic reticulum, and 2) the rest decay of contractility seen in feline ventricular myocytes results from time-dependent loss of Ca2+ from this organelle.
Dependence of Na-K pump current on internal Na+ in mammalian cardiac myocytes
Authors: Mogul D. J. , Singer D. H. , Ten Eick R. E.
Published: December 2017

Na-K pump current (Ipump) is a function of the intracellular Na+ concentration [( Na+]i). We examined the quantitative relationship between Ipump and [Na+]i in isolated guinea pig ventricular myocytes under steady-state conditions. [Na+]i was controlled and "clamped" at several selected concentrations using wide-tipped pipette microelectrodes, and membrane current was measured using the whole cell patch voltage-clamp technique. Ipump generated at a holding potential of -40 mV was determined by measuring the change in steady-state holding current before and during exposure to dihydroouabain (1 mM); Ipump was measured at 11 levels of [Na+]i ranging from 0 to 80 mM (n = 63) with only one measurement per cell and normalized to cell capacitance to account for differences between myocytes in sarcolemmal surface area. Ipump exhibited a nonlinear dependence on [Na+]i; a Hill analysis of the relationship yielded a half-maximal [Na+]i for pump stimulation of 43.2 mM and a Hill coefficient of 1.53. An alternative analysis of the experimental data was performed assuming that occupation of three internal binding sites by Na+ is required for enzyme turnover. Regression analysis gave the best fit when only two different binding affinities (KD) are postulated. The values are KD1 = 1 mM, KD2 = KD3 = 29 mM. From the analysis using the latter model, the level of [Na+]i at which Ipump saturated closely approximated the theoretical saturation level calculated from published estimates of pump turnover rate and density. The maximal sensitivity of the Na-K pump to changes in [Na+]i occurs when internal [Na+] is within the range for the normal resting physiological level.
Effects of hypoxia and reoxygenation on lung glutathione system
Authors: Jackson R. M. , Veal C. F.
Published: December 2017

Reexpansion pulmonary edema (RPE) parallels reperfusion (reoxygenation) injuries in other organs in that hypoxic and hypoperfused lung tissue develops increased vascular permeability and neutrophil infiltration after reexpansion. This study investigated the lung cellular glutathione system during hypoxia (produced by lung collapse) and after reoxygenation (produced by reexpansion). Two separate groups of rabbits were studied to determine effects of lung hypoxia-reoxygenation on 1) lung glutathione peroxidase and reductase enzyme activities and 2) lung tissue, plasma, and alveolar lavage fluid total (reduced glutathione plus glutathione disulfide) and oxidized glutathione. Neither lung collapse for 3-7 days nor reexpansion for 2 h after 7 days of collapse affected glutathione peroxidase [controls, 0.36 +/- 0.04 (left), 0.38 +/- 0.03 U/mg DNA (right)] or reductase [controls, 0.12 +/- 0.01 (left), 0.14 +/- 0.01 U/mg DNA (right)] activities. The concentration of glutathione disulfide increased markedly in right alveolar lavage fluid, but not in plasma, after right lung reexpansion. Right lung total glutathione decreased significantly (-19%) after 7 days of collapse. After right lung reexpansion, both left (-65%) and right (-68%) lung total glutathione decreased significantly. The percent of total glutathione present in the oxidized form increased significantly in both left (to 15.5 +/- 4.0% of total) and right (to 18.7 +/- 6.3% of total) lungs after reexpansion of the right lung. These data indicate that lung tissue hypoxia, produced by unilateral lung collapse, was associated with a unilateral decrease in lung total glutathione content. Right lung reoxygenation, due to rapid reexpansion, caused a bilateral decrease in lung total glutathione content and an increase in right lung and alveolar lavage fluid glutathione disulfide concentration.
Complement activation and white cell sequestration in postischemic skeletal muscle
Authors: Rubin B. B. , Smith A. , Liauw S. , Isenman D. , Romaschin A. D. , Walker P. M.
Published: December 2017

After skeletal muscle ischemia, tissue damage is augmented during reperfusion. White blood cells (WBCs) and complement proteins may participate in the reperfusion injury. The purpose of this study was to define the kinetics of classical and alternative pathway complement activation and WBC sequestration by postischemic skeletal muscle during the first 48 h of reperfusion in vivo. The isolated canine gracilis muscle model was used. Systemic levels of the complement proteins factor B (alternative pathway) and C4 (classical pathway) were quantitated by hemolytic assay. WBC sequestration was measured by gracilis arterial-venous WBC differences and tissue myeloperoxidase activity. Reperfusion was associated with an 18% decrease in systemic factor B levels but no consistent change in systemic C4 levels. WBCs were sequestered during the first 4 h of reperfusion, and tissue myeloperoxidase activity was elevated 97-fold after 48 h of reperfusion. These results suggest that skeletal muscle ischemia-reperfusion stimulates 1) activation of the alternative but not the classical complement pathway and 2) an immediate and prolonged sequestration of WBCs.
Reduced arachidonate metabolism in ATP-depleted myocardial cells occurs early in cell injury
Authors: Revtyak G. E. , Buja L. M. , Chien K. R. , Campbell W. B.
Published: December 2017

Exposure of cultured neonatal rat myocardial cells to metabolic inhibitors results in cellular ATP depletion. If prolonged, arachidonic acid is released from membrane phospholipid and irreversible cell injury may ensue. The present study was undertaken to identify the major products of arachidonic acid formed when myocardial cells are depleted of ATP by the metabolic inhibitors 2-deoxy-D-glucose (2-DG) and oligomycin (OG). Under basal conditions, myocardial cells metabolize [3H]arachidonic acid to 6-keto-[3H]prostaglandin (PG)F1 alpha, [3H]PGE2, [3H]PGF2 alpha, 12-[3H]hydroxy-6,8,11,14-eicosatetraenoic acid (12-[3H]HETE) and 11-[3H]HETE, indicating that these cells contain both cyclooxygenase and lipoxygenase pathways. After exposure of myocardial cells to 10 mM 2-DG and 0.1 micrograms/ml OG for 4 h, the basal release of 6-keto-PGF1 alpha and PGE2 is reduced by 3.4-fold and 2-fold, respectively. Supernatants obtained from cells prelabeled with [3H]arachidonic acid and treated with 2-DG and OG for 4 or 12 h did not contain detectable [3H]prostaglandins or [3H]HETEs, but only [3H]arachidonic acid when compared with untreated cells. After 4 and 12 h of treatment with 2-DG and OG, there was a 3.4- and 4.4-fold net release of endogenous arachidonic acid from treated compared with untreated cells. When stimulated with bradykinin, melittin (a phospholipase activator), or arachidonic acid, the synthesis of 6-keto-PGF1 alpha increased to a similar extent in both 2-DG- and OG-treated and -untreated cells. Hence, ATP-depleted myocardial cells do not convert arachidonic acid to oxygenated metabolites under basal conditions. The reduced arachidonic acid metabolism during ATP depletion is not due to direct inactivation of cyclooxygenase or membrane phospholipase. This impairment in arachidonic acid metabolism may represent an early event in myocardial cell injury.
Effect of perfusate rheology on the diastolic coronary pressure-flow relationship
Authors: Drossner M. , Aversano T.
Published: December 2017

The hypothesis that rheological properties of the coronary perfusate account for the curvilinearity and high zero-flow pressure (Pf = 0) of the diastolic coronary-pressure flow relationship (DCPFR) was tested by measuring these relationships using coronary perfusates of varying rheological character. In 16 open-chest, heart-blocked dogs the left circumflex coronary artery was cannulated and perfused using an extra-corporeal circuit, and autoregulation was abolished with intracoronary adenosine. DCPFRs were constructed from data obtained at multiple steady-state levels of coronary pressure during long diastoles while left ventricular diastolic pressure was held constant. Although isovolumic hemodilution reduced hematocrit from 46 +/- 3% to 32 +/- 3% and increased coronary conductance, it neither abolished the curvilinearity nor changed Pf = 0, which remained significantly higher than left ventricular diastolic pressure. In 10 additional animals, DCPFRs obtained during blood perfusion were compared with those obtained using crystalloid perfusate. Crystalloid perfusion increased coronary conductance and failed to abolish curvilinearity. However, with crystalloid perfusate, Pf = 0 was reduced to a value essentially equal to left ventricular diastolic pressure. We conclude that while the rheological properties of coronary perfusates do not fully account for the curvilinearity of the DCPFR, they do importantly influence coronary conductance and Pf = 0.
Angiotensin II stimulation of protein synthesis and cell growth in chick heart cells
Authors: Baker K. M. , Aceto J. F.
Published: December 2017

The octapeptide [Ile5]angiotensin II (ANG II), which is the principal circulating hormone of the renin-angiotensin system, could modulate or mediate cardiac hypertrophy via indirect effects, through increases in total peripheral vascular resistance, or by direct effects on cardiac cells, which result in increased protein synthesis and cell growth. In this study we determined whether ANG II stimulated protein synthesis and cell growth in cultures of embryonic chick myocytes. After 3 h of exposure to ANG II, there were significant increases in total cellular protein at 120, 144, and 168 h and in the relative rate of protein synthesis at 120 and 144 h. There was a significant increase in the fractional rate of protein synthesis of 32.2% (0.0119 +/- 0.0008 h-1 for ANG II stimulated and 0.0090 +/- 0.0003 h-1 for control). The stimulatory effects of ANG II on protein synthesis and cell growth were inhibited by the ANG II antagonist [Sar1,Ile8]ANG II and the hexapeptide ANG II-(3-8). ANG II significantly increased total RNA levels in myocytes, at 12 h after exposure to the peptide. The stimulatory effect of ANG II (32%) on total cellular protein was slightly greater than that seen with norepinephrine (20%) in contrast to the greater stimulatory effect seen with phorbol 12,13-dibutyrate (47%). ANG II and [Sar1,Ile8]ANG II each stimulated increases in cytosolic-free Ca2+, whereas ANG II-(3-8) did not. Growth-related effects of changes in the chronotropic state of the myocytes were excluded, in that, ANG II-stimulated increases in protein synthesis and cellular protein were not inhibited by potassium chloride depolarization of the cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of increased afterload on left ventricular function in closed-chest dogs
Authors: Freeman G. L.
Published: December 2017

Mechanical response of the left ventricle (LV) in an intact circulatory system to steady-state increases in afterload may differ from that of an isolated LV, because secondary hemodynamic changes cannot be independently manipulated when the circulation is intact. To evaluate the integrated response of the LV in closed-chest dogs to sustained increases in afterload, six animals chronically instrumented with three orthogonal diameter gauges and LV manometers were studied after autonomic blockade and fentanyl-droperidol anesthesia. End-systolic pressure-volume (PES-VES) and stroke work end-diastolic volume (SW-EDV) relations and the relations between pressure-volume area (PVA, area bounded by PV loop and PES-VES relation) and EDV were quantified. Balloon inflation (BI) in the proximal descending aorta increased LV PES from 100.7 +/- 13.4 to 140.2 +/- 19.3 mmHg (P less than 0.002) and LVEDV from 39.1 +/- 11.3 to 43.3 +/- 12.2 ml (P less than 0.01). The slope of the PES-VES relation was not significantly changed, whereas V100, a volume intercept in the common range of pressures, was reduced from 27.5 +/- 7.3 to 23.7 +/- 6.1 ml (P less than 0.005). PVA-EDV relation was highly linear; its slope was increased after BI. Comparison of beats with matched LVEDV before and after BI showed significant increases in maximum rate of pressure development and PVA; the change in SW after BI was modest and not significant. The efficiency of energy transfer from PVA to SW (TransPVA, SW/PVA X 100) decreased from 52.5 +/- 8.6 to 42.6 +/- 6.3% (P less than 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)
Depression of endothelium-dependent relaxation by filarial parasite products
Authors: Kaiser L. , Tithof P. K. , Williams J. F.
Published: December 2017

Endothelium-dependent relaxation is depressed in the femoral artery of dogs with heartworm, Dirofilaria immitis, infection. Moreover, in infected dogs, the mechanism of relaxation is different. Because D. immitis is located primarily in the pulmonary circulation, these findings suggested that D. immitis releases biologically active mediators that alter distal endothelium-dependent relaxation. We tested this hypothesis in vitro. Rings of rat aorta were exposed to D. immitis (alone, in 1,000 mol wt or 100 mol wt cutoff dialysis tubing, and bioassay with conditioned medium). D. immitis alone depressed relaxation to acetylcholine, carbachol, and A23187. Nitroglycerin relaxation was not affected. Depression of acetylcholine relaxation was seen with D. immitis alone, in 1,000 mol wt dialysis tubing, and bioassay with conditioned medium. However, acetylcholine relaxation with D. immitis in 100 mol wt dialysis tubing was not different from control. It appears that D. immitis releases a small, stable, biologically active factor that alters endothelium-dependent relaxation. Its exact nature is unknown. The study of endothelial cell behavior in filariasis and modulation of endothelial cell function by filarial factors may provide important clues in understanding the pathogenesis of parasitic diseases.
Membrane hyperpolarization is a mechanism of endothelium-dependent cerebral vasodilation
Authors: Brayden J. E.
Published: December 2017

Acetylcholine (ACh)-induced hyperpolarization of cerebral arteries requires a functional endothelium. The hyperpolarization is reversed by potassium-channel blockers. The goal of this study was to determine whether the hyperpolarization is causally related to endothelium-dependent dilation of isolated cerebral arteries. ACh hyperpolarized rabbit middle cerebral arteries by up to 19 mV. The hyperpolarizations were sustained and did not occur in arteries without endothelial cells or in the presence of potassium-channel inhibitors (3 x 10(-6) M glibenclamide or 5 x 10(-5) M BaCl2). ACh-induced dilator responses were inhibited but not abolished by glibenclamide or BaCl2. Methylene blue also inhibited the dilator responses, and a combination of glibenclamide or BaCl2 and methylene blue greatly diminished the dilation. Nitric oxide relaxed but did not hyperpolarize the vascular smooth muscle cells, and BaCl2 had no effect on the nitric oxide-induced relaxations. These data indicate that the overall cerebral arterial dilator response to ACh is determined by the combined effects of membrane hyperpolarization, which closes voltage-dependent calcium channels, and the actions of a second endothelial factor, probably endothelium-derived relaxing factor.
Role of peptidoleukotrienes in hypoxic pulmonary vasoconstriction in rats
Authors: McDonnell T. J. , Westcott J. Y. , Czartolomna J. , Voelkel N. F.
Published: December 2017

The role of leukotrienes in the mechanism of hypoxic pulmonary vasoconstriction (HPV) is controversial. To determine whether leukotriene C4 (LTC4) was produced during HPV, LTC4 levels were measured in individual samples of lung tissue, lung bronchoalveolar lavage fluid (BALF), and blood perfusate in isolated perfused lungs ventilated with normoxic or hypoxic gas mixtures. HPV was not associated with increased LTC4 in lung tissue or increased LTE4 in blood perfusate. Consistent with previous studies demonstrating elevated levels of LTC4 in pooled BALF fluid from hypoxic lungs, individual lung BALF samples demonstrated an elevation of LTC4 during hypoxia. However, the process of lung lavage alone stimulated eicosanoid production, with LTC4, 6-ketoprostaglandin F1 alpha, and thromboxane B2 levels being higher in lavaged compared to non-lavaged lungs. In lungs to which the lipoxygenase inhibitor AA 861 was added to the perfusate, a reduction in the lung tissue LTC4 levels was observed without any or only a slight reduction in HPV. To evaluate the physiological effects of LTC4 in the airways, exogenous LTC4 (1-1,000 ng) was added to the airways of both blood- and physiological salt solution-perfused lungs without any effect on the pulmonary artery pressure or a response to hypoxia. These results do not support the hypothesis that leukotrienes mediate HPV in the rat.
Endothelium and mechanical responses of isolated monkey pulmonary veins to histamine
Authors: Matsuki T. , Ohhashi T.
Published: December 2017

Ring strips of monkey pulmonary veins precontracted with a high concentration of prostaglandin F2 alpha (PGF2 alpha) relaxed in a concentration-dependent manner in response to histamine. Treatment with mepyramine and/or famotidine attenuated the relaxation. 2-Pyridylethylamine (2PEA) and dimaprit caused relaxations in the precontracted preparations, which were inhibited by pretreatment with mepyramine and famotidine, respectively. Removal of endothelium reversed the histamine- and 2PEA-induced relaxations to dose-related contractions. On the other hand, the removal had no effect on the dimaprit-induced relaxations, which were significantly reduced by pretreatment with famotidine. Histamine-induced relaxations in the precontracted strips with endothelium in the presence and absence of famotidine were suppressed or abolished by treatment with methylene blue or hemoglobin but were unaffected by aspirin. It may be concluded that histamine-induced relaxation in monkey pulmonary veins precontracted with PGF2 alpha is mediated by H2-receptors in smooth muscle and H1-receptors in endothelium. Also, stimulation of the endothelial H1-receptors liberates an endothelium-derived relaxing factor.
Superoxide anion inhibits cGMP-associated bovine pulmonary arterial relaxation
Authors: Cherry P. D. , Omar H. A. , Farrell K. A. , Stuart J. S. , Wolin M. S.
Published: December 2017

We have reported evidence that endothelium-independent relaxations of isolated bovine pulmonary arteries to H2O2 and to reoxygenation with 95% O2-5% CO2 after brief exposure to N2 (5% CO2) appear to be mediated by the activation of guanylate cyclase via H2O2 metabolism through catalase. Treatment of endothelium-removed pulmonary arteries with a potential guanylate cyclase-inhibitor, LY 83583, or with the inhibitor of the Zn+2, Cu+2-superoxide dismutase (SOD) diethyldithiocarbamic acid (DETCA), antagonized guanosine 3',5'-cyclic monophosphate (cGMP)-associated relaxation to H2O2, to reoxygenation and to glyceryl trinitrate, but not the adenosine 3',5'-cyclic monophosphate-associated relaxation to isoproterenol. Superoxide anion (O2-.) levels, detected by lucigenin-elicited chemiluminescence, were enhanced by LY 83583 or DETCA treatment of pulmonary arteries at ambient PO2. Chemiluminescence produced by LY 83583 was markedly potentiated by DETCA treatment, decreased at addition of exogenous SOD, and inhibited markedly by anoxia. LY 83583, but not DETCA, stimulated cyanide-insensitive O2 consumption, consistent with redox cycling of the compound independent of mitochondrial respiration. We propose that O2-. generated on the metabolism of LY 83583, or from cellular electron donors after SOD inhibition by DETCA, inhibits cGMP-mediated relaxations of pulmonary arteries.
Deformation response of red blood cells in oscillatory shear flow
Authors: Nakajima T. , Kon K. , Maeda N. , Tsunekawa K. , Shiga T.
Published: December 2017

The characteristics of red cell deformation were studied, focusing on deformation response of the cells subjected to oscillatory shear stress. Red blood cells were fractionated into subpopulations of different densities, i.e., low-density and high-density cells. The deformation response of the fractionated cells was evaluated with a rheoscope varying their intracellular viscosity and oscillation frequency of the applied shear stress, and determinants of the deformation response were compared with those of whole cell deformation under stationary shear stress. When the fractionated cells were exposed to sinusoidally oscillated shear stress, the cells underwent oscillatory deformation. The degree of deformation of the low-density cells correspond to the magnitude of the applied shear stress up to an oscillation frequency of 2.7 Hz. Meanwhile, such an oscillatory deformation as to correspond to the applied shear stress was observed up to 1.7 Hz for the high-density cells. It was suggested that intracellular viscosity was an important factor to determine the deformation response of red cells to oscillatory shear stress.
Cardiovascular responses to vasoactive intestinal contractor, a novel endothelin-like peptide
Authors: Minkes R. K. , Higuera T. R. , Rogers G. F. , Sheldon E. A. , Langston M. A. , Kadowitz P. J.
Published: December 2017

Cardiovascular and pulmonary responses to vasoactive intestinal contractor (VIC), an endothelin (ET)-like peptide from the murine gastrointestinal tract, were investigated in the cat. VIC (0.1-1.0 nmol/kg iv) decreased or elicited biphasic changes in arterial pressure (AP) and increased central venous pressure, cardiac output, pulmonary arterial pressure, and left atrial pressure. VIC produced biphasic changes in systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR). VIC increased heart rate (HR) and, at the 1 nmol/kg dose, a secondary decrease was observed. Hexamethonium blocked the changes in HR in response to VIC, whereas the ganglionic blocker, meclofenamate, or glybenclamide had no effect on changes in AP, SVR, and PVR elicited by the peptide. VIC caused small changes in right ventricular contractile force and increased distal aortic and carotid artery blood flow at all doses, with secondary decreases at the higher doses. VIC decreased superior mesenteric artery flow and decreased renal blood flow at the 1 nmol/kg dose. The changes in AP in response to VIC, ET-1, and ET-2 were similar, whereas those elicited by ET-3 and sarafotoxin 6b were similar. The present data show that VIC can produce both vasodilation and vasoconstriction in the systemic vascular bed and biphasic changes in PVR in the cat. These data show that VIC can produce complex cardiovascular responses similar to those elicited by the ET peptides and that these responses are largely independent of autonomic reflexes, release of cyclooxygenase products, and activation of ATP-regulated potassium channels. We conclude that VIC may act as an ET-like peptide.
Extracellular pH modulates block of both sodium and calcium channels by nicardipine
Authors: Gilliam F. R. , Rivas P. A. , Wendt D. J. , Starmer C. F. , Grant A. O.
Published: December 2017

Slowing of the recovery of the Na channel from local anesthetic block at low external pH has been well described. In contrast the Ca channel has been reported not to show such an effect. Because of the absence of this response, a two-site model for the interaction of Ca antagonists with the Ca channel has been proposed. We sought to determine whether these results were a consequence of utilizing the poorly lipid-soluble Ca antagonist diltiazem as the test drug. We have measured the time constants of recovery (tau r) of Na (INa) and Ca currents (ICa) recorded from rabbit atrial myocytes during control and exposure to the lipid-soluble Ca antagonist nicardipine as external pH was reduced from 7.8 to 6.9. In the absence of drug, tau r for INa decreased from 19 +/- 1.3 to 12.1 +/- 0.6 ms for the pH reduction. Similarly, tau r for ICa decreased from 53 +/- 7 to 33.6 +/- 7 ms. During exposure to nicardipine tau r for INa increased from 2.24 +/- 0.8 to 5.96 +/- 0.8 s as external pH was reduced. For ICa, tau r also increased from 1.43 +/- 0.55 to 2 +/- 0.32 s. For each channel type, the results are well explained by a single blocking site model with hydrophobic and hydrophilic pathways to a single membrane binding site as proposed by Hille (J. Gen. Physiol. 69: 497-517, 1977).
Different activation of L-arginine pathway by bradykinin, serotonin, and clonidine in coronary arteries
Authors: Richard V. , Tanner F. C. , Tschudi M. , Luscher T. F.
Published: December 2017

Endothelial cells release nitric oxide from L-arginine, and this pathway can be inhibited by the analogue of L-arginine, NG-monomethyl-L-arginine (L-NMMA). The effect of L-NMMA on endothelium-dependent relaxation of epicardial porcine coronary arteries was studied in isolated blood vessels suspended in organ chambers for isometric tension recording. Endothelium-dependent relaxations to bradykinin, serotonin, and the alpha 2-adrenergic agonist clonidine were evaluated in the presence and absence of L-NMMA (10(-5)-10(-3) M). L-NMMA, as well as the inhibitor of guanylate cyclase methylene blue (10(-5) M) and hemoglobin (10(-5) M), inhibited endothelium-dependent relaxation to serotonin and clonidine. The effect of L-NMMA could be reversed by L-arginine but not by D-arginine. In contrast, L-NMMA, methylene blue, and hemoglobin caused a weak inhibition of the endothelium-dependent relaxation evoked by bradykinin; indomethacin and tranylcypromine had no effect. The inhibitor of Gi proteins pertussis toxin (100 ng/ml) abolished the relaxations evoked by clonidine and markedly reduced those evoked by serotonin but did not affect those caused by bradykinin. In the presence of pertussis toxin, L-NMMA induced a further reduction of the relaxations to serotonin, suggesting that inhibition of Gi proteins does not completely prevent the activation of the L-arginine pathway. Thus endothelium-dependent relaxations to serotonin and to the alpha 2-adrenergic agonist clonidine are mediated through the release of nitric oxide formed from L-arginine in endothelial cells, whereas bradykinin evokes endothelium-dependent relaxations via a different pathway.
Permeability of time-dependent K+ channel in guinea pig ventricular myocytes to Cs+, Na+, NH4+, and Rb+
Authors: Hadley R. W. , Hume J. R.
Published: December 2017

Currents through time-dependent K+ channels (also referred to as IK or the delayed rectifier) were studied with the whole cell patch-clamp technique in isolated guinea pig ventricular myocytes. IK measurements were restricted to the examination of deactivation tail currents. Substitution of various monovalent cations for external K+ produced shifts of the reversal potential of IK. These shifts were used to calculate permeability ratios relative to K+. The permeability sequence for the IK channels was K+ = Rb+ greater than NH4+ = Cs+ greater than Na+. Time-dependent outward currents were also examined when the myocytes were dialyzed with Cs+ instead of K+. A sizeable time-dependent outward current, quite similar to that seen with K+ dialysis, was demonstrated. This current was primarily carried by intracellular Cs+, as the reversal potential of the current shifted 46 mV per 10-fold change of external Cs+ concentration. The significance of Cs+ permeation through IK channels is discussed with respect to the common use of Cs+ in isolating other currents.
Dynamic mechanisms of cardiac oxygenation during brief ischemia and reperfusion
Authors: Parsons W. J. , Rembert J. C. , Bauman R. P. , Greenfield J. C. , Piantadosi C. A.
Published: December 2017

Myocardial oxygenation may be altered markedly by changes in tissue blood flow. During brief ischemia and reperfusion produced by transient occlusion of the left anterior descending artery in 10 open-chest dogs, changes in the oxygenation of tissue hemoglobin (Hb) plus myoglobin (Mb) and the oxidation-reduction (redox) state of mitochondrial cytochrome aa3 were monitored continuously using near-infrared spectroscopy. The nondestructive optical technique indicated that coronary occlusion produced an abrupt drop in tissue oxygen stores (tHb02 + Mb02), tissue blood volume (tBV), and the oxidation level of cytochrome aa3. Changes in the cytochrome oxidation state were related inversely to transmural collateral blood flow within the ischemic region (r = 0.77) measured with radiolabeled microspheres. Furthermore, there was a direct relationship (r = 0.91) between collateral blood flow and the tissue level of desaturated Hb and Mb (tHb + Mb). Reperfusion after 2 min of ischemia led to a synchronous overshoot of baseline in coronary flow and tBV followed by supranormal increases in tHb + Mb02 and the oxidation level of cytochrome aa3. The tHb + Mb level increased transiently during reperfusion. This response correlated inversely with collateral flow during ischemia (r = 0.91). Accordingly, the time required to reach peak tHb + Mb levels was shortest in dogs with high collateral flows (r = 0.75). Thus collateral blood flow partially sustains myocardial oxygenation during coronary artery occlusion and influences tissue reoxygenation early during reperfusion.
Recombinant human interleukin 1 alpha dilates pial arterioles and increases cerebrospinal fluid prostanoids in piglets
Authors: Shibata M. , Leffler C. W. , Busija D. W.
Published: December 2017

Effects of recombinant human interleukin 1 alpha (IL-1 alpha) on vasomotor tone of pial arterioles and cerebrospinal fluid (CSF) prostanoid levels were examined in anesthetized piglets by employing the closed cranial window method. IL-1 alpha in a dose of 10.8 micrograms infused under the window increased pial arteriolar diameter [initial size, 160 +/- 9 (SE) micrograms] significantly at 15 min postinfusion through 30 min (30-min study), exhibiting a maximum dilation of 13 +/- 1% (n = 8) over the control levels. Significant increases in levels of prostaglandin E2 (PGE2, 75%), 6-keto-PGF1 alpha (84%), and PGF2 alpha (35%) but not for thromboxane B2 (TxB2, 2%) were observed when CSF was sampled from under the window 30 min after 10.8 micrograms IL-1 alpha. A lower dose of IL-1 alpha (1.0 micrograms, n = 4) significantly increased the diameter of pial arterioles with a tendency for longer onset (25-30 min) and smaller magnitude (9-10%) than the higher dose. In IL-1 alpha time-response studies, CSF sampled 10 min after 10.8 micrograms IL-1 alpha infusion (10-min study, n = 6) under the window exhibited the same levels of PGE2, 6-keto-PGF1 alpha, PGF2 alpha, and TxB2 as those of the controls. There was no vasodilation in the 10-min study. However, when sampled 20 min after 10.8 micrograms IL-1 alpha (20-min study, n = 6), CSF levels of all prostanoids except for TxB2 significantly increased over the controls.(ABSTRACT TRUNCATED AT 250 WORDS)
Nature of defibrillation: determinism versus probabilism
Authors: Deale O. C. , Wesley R. C. , Morgan D. , Lerman B. B.
Published: December 2017

The gradual transitions that are found between unsuccessful and successful shock strengths in percent success or dose-response curves suggest that defibrillation is a probabilistic phenomenon. This concept appears to be reinforced by the fact that a frequency distribution is observed in defibrillation threshold data and that a dose-response relationship is also obtained by integration of the frequency distribution. The purpose of this study was to investigate whether a deterministic threshold model (based on experimental results) could produce 1) gradual transitions in dose-response curves, and 2) a threshold frequency distribution for individual subjects. In the experimental phase of the study, a linear deterministic relationship was found between transthoracic threshold current and defibrillation episode number (other variables held constant) in pentobarbital-anesthetized dogs. The correlation coefficient for each dog was between 0.77 and 0.98 (P less than 0.01), and both positive and negative slopes were found. Based on these results, threshold current was modeled for computer simulation as a linear function of episode number. The model was thus purely deterministic with no random variability. For each simulated experiment, several parameters were varied: order of shocks (increment, decrement, random order), slope of threshold function, and percent error of the initial threshold. Several hundred computer simulations were performed to determine the effect of varying these parameters. In all cases, threshold-frequency distributions and sigmoidal dose-response curves with gradual transitions were produced. The results of this investigation demonstrate that the apparent probabilistic behavior of defibrillation can be produced by a deterministic relationship.
Myocardial electrophysiological effects of vasoactive intestinal peptide in dogs
Authors: Kralios A. C. , Anderson F. L. , Kralios F. A.
Published: December 2017

Vasoactive intestinal peptide (VIP) is a potent inotrope and coronary vasodilator. To test whether VIP also exerts regional myocardial electrophysiological (EP) effects, dose-response and time-course effects of intracoronary injections (10(-10)-10(-4) M) were obtained in 4 intact hearts and 12 in situ normoperfused right ventricular flap preparations in chloralose-anesthetized dogs. Under constant rate, activation (A), recovery (R), and A-R interval (ARI) maps were constructed from multiplexed unipolar surface electrograms recorded simultaneously from 32 sites. Effects were compared with those of isoproterenol (Iso) and forskolin (For). The main finding with all agonists was the uniform shortening of ARIs in a dose-response fashion with a maximum of 30 +/- 4 ms or 20% from control. Although the maximal EP changes were similar for all agonists, they occurred at different molecular concentrations (10(-6) Iso, 10(-5) VIP, and 10(-4) For). Also, whereas the duration of EP effect did not exceed 5 min for Iso and For, it was markedly sustained for VIP, outlasting its contractile but paralleling its vasodilatory effect. The physiological endoepicardial differences in ARI and the recovery sequence were preserved for all agonists. Thus VIP, in addition to coronary vasodilation and myocardial inotropy, exerts a strong balanced global myocardial EP effect, similar to, but more sustained than, the adrenergic effect. The difference in duration of inotropic and EP effects may point to different mediating mechanisms.
Quinidine blocks adenosine 5'-triphosphate-sensitive potassium channels in heart
Authors: Undrovinas A. I. , Burnashev N. , Eroshenko D. , Fleidervish I. , Starmer C. F. , Makielski J. C. , Rosenshtraukh L. V.
Published: December 2017

The ATP-sensitive potassium channel current (IK-ATP) was studied in excised inside-out patches from rat ventricular cells at 20-23 degrees C. The bath solution contained 140 mM KF, and the pipette solution contained 140 mM KCl and 1.2 mM MgCl2. ATP (0.5 mM) in the bath inhibited IK-ATP. In the absence of ATP, 10 microM quinidine decreased open probability 67 +/- 1% (n = 6) at -50 mV and 28 +/- 12% at -130 mV (n = 5) without affecting single channel conductance (48-52 pS). The block increased with 25 and 50 microM quinidine and could be reversed on washing quinidine for several minutes. Interburst (closed) intervals were increased by quinidine, whereas open and closed time distributions within bursts were not changed. We conclude that quinidine blocks IK-ATP in a "slow" and voltage-dependent manner in clinically relevant concentrations. Because of the postulated role for IK-ATP in cardiac ischemia, quinidine block of this channel may play a role in ischemic arrhythmias.