bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of acute hypoxemia on brain blood flow and oxygen metabolism in immature fetal sheep
Authors: Gleason C. A. , Hamm C. , Jones M. D.
Published: December 2017

Studies of cerebral blood flow and oxygen metabolism during acute hypoxic hypoxia in fetal sheep have been confined to late gestation, a time when brain development in this species is largely complete. There is no systematic study of cerebral vascular responses to acute hypoxic hypoxia in immature fetal sheep or, indeed, in immature brains of any species. We studied 13 fetal sheep in utero at 93 +/- 1 days gestation (term = 145-150 days), 48 h after intravascular catheters were placed into the superior sagittal sinus, axillary arteries, and inferior vena cava. We measured brain blood flow by the microsphere method. Cerebral oxygen consumption was calculated with the use of blood flow to the cerebral hemispheres (cerebrum, diencephalon, mesencephalon) and arterial and sagittal sinus values for oxygen content. Fractional oxygen extraction was calculated as the ratio between oxygen consumption and oxygen transport. We altered fetal oxygenation by changing the mother's inspired oxygen concentration. As in the near-term fetus, acute hypoxic hypoxia resulted in increased blood flow to cerebral hemispheres, cerebellum, and pons-medulla; furthermore, the increase in blood flow was sufficient to sustain cerebral oxygen consumption. However, in contrast to near-term fetuses, the increase in blood flow to the cerebral hemispheres was not sufficient to maintain convective oxygen transport. Cerebral oxygen consumption was therefore sustained in part by an increase in fractional extraction. Blunted hypoxic vasodilation in immature fetuses might reflect either immature regulatory mechanisms or an inability of cerebral vessels to respond to the usual stimuli. It is also possible that hypoxic vasodilation was blunted by reflex stimulation of the sympathetic nervous system.
Oxidative and glycolytic ATP formation of rabbit papillary muscle in oxygen and nitrogen
Authors: Mast F. , Elzinga G.
Published: December 2017

Contraction-related O2 consumption of rabbit papillary muscles was determined at 20 degrees C by measuring change in saline PO2 during and after trains of 120 twitches at 0.125-1 Hz in a microrespirometer. Although anoxic cores occurred at twitch frequencies greater than 0.2 Hz, no lactate was found in saline after twitch train. To measure lactate accumulation in muscle, fully oxygenated muscles were frozen at rest and during steady-state twitches at 0.2 Hz. We also measured nucleotides and creatine (Cr) compounds. There were no differences in lactate, ATP, and phosphocreatine (PCr) content between the resting and active muscles. When a P-to-O2 ratio of 6.3 is assumed, aerobic ATP formation was compared with glycolytic ATP formation during anoxia at a stimulus frequency of 0.2 Hz. The latter value was obtained by freezing muscles between 6 and 25 min after changing from O2- to N2-saturated saline. Withdrawal of O2 caused the ratio of PCr to total Cr to fall in less than 6 min from 0.77 to 0.23, while ATP remained at approximately 15 mumol/g dry wt. Force fell initially within 4 min to approximately 70% of control value, decreasing thereafter more slowly to approximately 40% at 20 min. From the relationship between amount of lactate formed and duration of anoxia, rate of anaerobic ATP formation was calculated assuming a P-to-lactate ratio of 1. We found that despite continuing contractile activity, anaerobic ATP formation was less than that required by a fully oxygenated resting muscle and was about the same magnitude as the estimated ATP hydrolysis for the contractions in N2. We conclude that in fully oxygenated rabbit papillary muscles no net lactate is produced during stimulation and that in anoxia anaerobic glycolytic capacity may not provide sufficient ATP for processes other than the uptake of Ca by the sarcoplasmic reticulum and cross-bridge cycling.
Effect of lactic acidosis on canine hemodynamics and left ventricular function
Authors: Teplinsky K. , O'Toole M. , Olman M. , Walley K. R. , Wood L. D.
Published: December 2017

Hypoperfusion states cause lactic acidosis, and the acidemia further reduces the inadequate cardiac output. Conceivably, the adverse effect of lactic acidemia on cardiac output is due to depressed contractility demonstrated in isolated myocardium. Alternatively, factors governing venous return cause a relative hypovolemic state and/or acidemic pulmonary vasoconstriction-induced right ventricular dysfunction. We reasoned that examination of left ventricular pressure-volume relationships at end systole and end diastole would determine which of these potential mechanisms accounted for reduced cardiac output during progressive lactic acidosis in anesthetized, mechanically ventilated dogs. Left ventricular (LV) volume was estimated from two pairs of epicardial ultrasonic crystals placed in the anterior-posterior and longitudinal planes, and LV pressure was obtained rom a catheter-tipped transducer. During progressive acidemia induced by a continuous intravenous infusion of 0.5 N lactic acid, cardiac output, stroke volume, and mean systemic arterial pressure fell significantly while mean pulmonary artery pressure and right atrial pressure increased significantly. These variables did not change with time in control (no-acid infusion) dogs. Lactic acidemia caused a 40% reduction in stroke volume, which could be attributed to depressed LV contractility, characterized by a decrease in maximum dP/dt as well as a fall in slope (Emax) with no change in volume intercept (Vo) of the left ventricular pressure-volume relationship at end systole. Neither the measured left ventricular end-diastolic pressure nor the estimated left ventricular end-diastolic volume (LVEDV) decreased with acidemia, suggesting that the reduced venous return did not result from relative hypovolemia. However, acidemic pulmonary hypertension may have interfered with the expected response to myocardial depression, which is an increase in LVEDV.
Pulmonary vascular effects of prostaglandin D2 in newborn pig
Authors: Perreault T. , Coe J. Y. , Olley P. M. , Coceani F.
Published: December 2017

In the lamb, prostaglandin (PG) D2 dilates the fetal and early neonatal pulmonary vasculature but becomes a constrictor in the older animal. Constriction could result from conversion of PGD2 to 9 alpha,11 beta-PGF2, stimulated formation of an endogenous vasoactive agent, or a change in PGD2 receptor function. An answer to the latter question was sought in the newborn pig using an isolated lung preparation (1, 3, 7 days of age) and the anesthetized, acutely instrumented animal (1 day old). In vitro, PGD2 increased pulmonary vascular resistance (PVR) in a dose- (2-340 ng/g dry lung) and age-dependent fashion under both normoxia (basal or raised tone) and hypoxia. At 1 and 7 days of age, indomethacin (3 X 10(-6) M) blunted the PGD2 constriction by 50%. Likewise, a thromboxane (Tx) A2 receptor antagonist (ONO 3708, 6 X 10(-8) M) curtailed the PGD2 response. In contrast, a TxA2 synthesis inhibitor (OKY 1581, 10(-6) M) was effective (approximately 70% inhibition) only in the 7-day-old animal. 9 alpha,11 beta-PGF2 and PGF2 alpha, also increased PVR in a dose- and age-related manner, although their action was weaker. Conversely, the 9-epoxy,11-methano endoperoxide analogue was the most potent pulmonary vasoconstrictor among the agents tested. In vivo, PGD2 (0.25-1 microgram/kg) constricted both pulmonary and systemic circulations. We conclude that the porcine pulmonary circulation, unlike the lamb circulation, is constricted by PGD2 throughout the neonatal period. This effect is mediated, in part, by a cyclooxygenase product. The increase in the PGD2 response with age cannot be ascribed to conversion to 9 alpha,11 beta-PGF2, since such occurrence would result in reduced effectiveness.
Estrogen effects on lymph flow as a function of outflow pressure in ewes
Authors: Valenzuela G. J. , Kim S.
Published: December 2017

The purpose of the present study was to assess whether acute estrogen administration decreased the lymphatic vessel's "pumping" ability. An additional goal was to assess whether estrogen affected the capillary filtration (used here as the total transfer of fluid and protein across the capillaries evidenced by the thoracic duct lymph flow rate). We reasoned that if estrogen administration decreases the lymph pumping ability against outflow pressure, then this phenomenon could help to explain the interstitial fluid retention seen during chronic estrogen. In six nonpregnant ewes we studied the thoracic lymph flow rate measured at different outflow pressures, before and after the acute administration of 50 mg of Premarin (conjugated estrogenic hormones). We also continuously determined arterial and venous pressures and heart rate. The arterial pressure declined from a mean of 99 +/- 0.33 (SE) mmHg to 95.4 +/- 0.2 mmHg (P less than 0.05) after the administration of estrogen. Heart rate increased from 88.5 +/- 0.8 to 111.3 +/- 1.2 beats/min (P less than 0.01). Venous pressure, plasma and lymph protein concentrations, and hematocrit did not change significantly (P greater than 0.1). Lymph flow rate declined progressively when measured against positive outflow pressure, whereas it remained stable when measured against negative pressure. Lymph flow rate during negative outflow pressure was higher after the administration of estrogen 0.044 +/- 0.002 vs. 0.032 +/- 0.002 ml.min-1.kg-1 for the control period (P less than 0.05). The calculated outflow pressure at which lymph flow rate became zero was similar for the period before or after the estrogen administration (P greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)
Reduced substrate oxidation in postischemic myocardium: 13C and 31P NMR analyses
Authors: Lewandowski E. D. , Johnston D. L.
Published: December 2017

13C and 31P nuclear magnetic resonance (NMR) spectra were used to assess substrate oxidation and high-energy phosphates in postischemic (PI) isolated rabbit hearts. Phosphocreatine (PCr) increased in nonischemic controls on switching from glucose perfusion to either 2.5 mM [3-13C]pyruvate (120%, n = 7) or [2-13C]acetate (114%, n = 8, P less than 0.05). ATP content, oxygen consumption (MVO2), and hemodynamics (dP/dt) were not affected by substrate availability in control or PI hearts. dP/dt was 40-60% lower in PI hearts during reperfusion after 10 min ischemia. Hearts reperfused with either pyruvate (n = 11) or acetate (n = 8) regained preischemic PCr levels within 45 s. Steady-state ATP levels were 55-70% of preischemia with pyruvate and 52-60% with acetate. Percent maximum [4-13C]glutamate signal showed reduced conversion of pyruvate to glutamate via the tricarboxylic acid (TCA) cycle at 4-min reperfusion (PI = 24 +/- 4%, means +/- SE; Control = 48 +/- 4%). The increase in 13C signal from the C-4 position of glutamate was similar to control hearts within 10.5 min. The increase in [4-13C]glutamate signal from acetate was not different between PI and control hearts. The ratio of [2-13C]Glu:[4-13C]Glu, reflecting TCA cycle activity, was reduced in PI hearts with acetate for at least 10 min (Control = 0.76 +/- 0.03; PI = 0.51 +/- 0.09) until steady state was reached. Despite rapid recovery of oxidative phosphorylation, contractility remained impaired and substrate oxidation was significantly slowed in postischemic hearts.
Measurement of cytoplasmic calcium in single microvessels with increased permeability
Authors: He P. , Pagakis S. N. , Curry F. E.
Published: December 2017

We investigated the hypothesis that an increase in cytoplasmic calcium ion concentration, [Ca2+]i, is one of the mechanisms responsible for increased microvessel permeability. We loaded the cells forming the walls of individually perfused microvessels in frog mesentery with fura-2 and measured [Ca2+]i in the control state and after adding the Ca2+ ionophore ionomycin to the perfusate. [Ca2+]i in the control state was 65 +/- 6 nM and increased to an initial peak of 285 +/- 29 nM after 1-3 min. After 4, 6, and 10 min, [Ca2+]i was 199 +/- 18, 163 +/- 16, and 129 +/- 9 nM, respectively. [Ca2+]i fell back to 77 +/- 7 nM after ionophore was removed. In similar experiments, hydraulic conductivity (Lp) increased to a peak of 9.5 times control after 1-3 min, then fell to 2.0 times control after 6 min. Lp remained elevated at this level for as long as ionophore was present in the perfusate. [Ca2+]i modulates the initial and sustained phases of the permeability increase. Both processes depend on external Ca2+ influx. Our experiments provide the first direct measurement of [Ca2+]i during a change in the permeability of an intact microvessel.
Ventricular hypertrophy and presynaptic regulation of sympathetic function
Authors: Schmid P. G. , Whiteis C. A. , Lund D. D.
Published: December 2017

In normal heart, presynaptic cholinergic muscarinic and alpha 2-adrenergic mechanisms contribute to regional variations in the rate constant of norepinephrine turnover (kNE), an index of sympathetic neural function. To evaluate these mechanisms in the hypertrophied heart, pulmonary artery-constricted and sham-operated guinea pigs were pretreated with 1) saline vehicle (control) or 2) a combination of quinuclidinyl benzilate (Q), a muscarinic cholinergic antagonist, and yohimbine (Y), an alpha 2-adrenergic antagonist. An increase in kNE was determined in multiple regions of heart from incorporation of radiolabeled tyrosine into norepinephrine during a control period at 24 degrees C and again at 4 degrees C. In sham animals, kNE during cold stress was increased significantly (P less than 0.05) by Q + Y compared with vehicle, confirming that muscarinic cholinergic and/or alpha 2-adrenergic receptors exert a negative-feedback influence on sympathetic neurotransmitter synthesis. In pulmonary artery-constricted animals, in contrast, there were smaller increases in cardiac kNE compared with sham guinea pigs given Q + Y and subjected to cold stress. These data support the concept that muscarinic cholinergic and/or alpha 2-adrenergic presynaptic regulation of cardiac sympathetic function is altered in the hearts and vasculature of pulmonary artery-constricted guinea pigs.
Effects of long-term increases in plasma ANP on angiotensin II-induced hypertension
Authors: Granger J. P. , Blaine E. H. , Stacy D. L. , La Rock M. J.
Published: December 2017

In vitro studies have suggested that atrial natriuretic peptide (ANP) is a potent antagonist of the vasoconstrictor actions of angiotensin II (ANG II). The purpose of this study was to determine the long-term effects of physiological increases in circulating levels of ANP on arterial pressure (AP) regulation in conscious dogs (n = 9) with ANG II-induced hypertension. Infusion of ANG II at a rate of 10 ng.kg-1.min-1 for 7 days increased AP from 85 +/- 3 to 133 +/- 4 mmHg. This increase in AP was associated with an increase in total peripheral resistance (TPR) and a decrease in cardiac output (CO). After 7 days of ANG II infusion, ANP103-126 was then infused simultaneously at a rate of 20 ng.kg-1.min-1 for 7 days. Plasma levels of ANP increased from 59 +/- 15 to 285 +/- 28 pg/ml. Increasing plasma ANP levels for 7 days had no significant long-term effect on AP (133 +/- 4 vs. 125 +/- 6 mmHg), TPR, or CO. There were also no significant changes in glomerular filtration rate or sodium excretion during the 7 days of ANP infusion. These data indicate that long-term increases in circulating levels of ANP have minimal chronic hypotensive effects in dogs with ANG II hypertension. In addition, the results from this study suggest that physiological increases in plasma ANP do not exhibit long-term antagonistic effects toward the vasoconstrictor actions of ANG II.
Alterations of intercellular junctions induced by hypoxia in canine myocardium
Authors: Hoyt R. H. , Cohen M. L. , Corr P. B. , Saffitz J. E.
Published: December 2017

To delineate potential structural mechanisms of impaired cell coupling induced by hypoxia in canine myocardium, we characterized derangements in intercellular junctions and alterations in the space constant in strips of ventricular epimyocardium before and after selected intervals of hypoxia in vitro. Tissue samples were analyzed morphometrically with transmission and freeze-fracture electron microscopy. Space constants in control tissues averaged 1.61 +/- 0.47 mm (mean +/- SD). After 30 and 60 min of hypoxia, space constants declined by 0.24 +/- 0.22 and 0.32 +/- 0.17 mm, respectively (P less than 0.05 vs. control in each case). Impaired coupling was not reversible with reoxygenation. Focal pathological separation of intercalated disk membranes was observed after 30 min of hypoxia, but morphometric analysis demonstrated no reduction in gap junction surface density to account for uncoupling after 30 min of hypoxia. However, after 60 min of hypoxia, gap junction surface density was reduced by 45%. Quantitative analysis of freeze-fractured gap junction replicas after 30 min of hypoxia revealed a significant decrease in P-face particle diameter from 8.51 +/- 1.64 nm in control tissues to 7.25 +/- 1.33 nm (P less than 0.01) with no further change at 60 min. Thus impaired coupling at 30 min is likely related to a change in the gap junction particle. Further uncoupling after 60 min of hypoxia is likely related, in addition, to reduced gap junction surface density. These results suggest that alterations in P-face particles and gap junction surface density are important determinants of progressive cellular uncoupling induced by hypoxia.
Progressive microcirculatory changes caused by hypercholesterolemia in rats
Authors: Schuschke D. A. , Saari J. T. , Ackermann D. M. , Miller F. N.
Published: December 2017

The progressive microcirculatory changes caused by hypercholesterolemia were studied in the rat cremaster model by use of intravital microscopy. Male Sprague-Dawley rats were fed either a normal chow diet or a chow diet supplemented with 1% cholesterol and 0.5% cholic acid for 1, 3, or 5 wk before experimentation. After 3 wk on the diet, hypercholesterolemia produced a significantly decreased vasoconstrictor response to norepinephrine in both arterioles and venules. After 5 wk, there was also significantly reduced macromolecular leakage induced by exogenous histamine and compound 48/80 in the high-cholesterol group. However, there was no change in the degree of base-line macromolecular leakage. Platelet thrombi formation induced by light activation of intravascular fluorescein isothiocyanate tagged to bovine serum albumin was slightly increased by hypercholesterolemia. Despite these microcirculatory changes there was no microscopic evidence of atheromatous pathology after 5 wk on the cholesterol diet. These results suggest a progressive nonspecific receptor desensitization and decreased inflammatory response shortly after the initiation of elevated serum cholesterol but before any histological evidence of atherosclerosis.
Local blood flow measured by fluorescence excitation of nonradioactive microspheres
Authors: Morita Y. , Payne B. D. , Aldea G. S. , McWatters C. , Husseini W. , Mori H. , Hoffman J. I. , Kaufman L.
Published: December 2017

An X-ray fluorescence system with low Compton background and high counting efficiency was developed to measure regional blood flow with nonradioactive microspheres. The performance of the system was tested in vitro by counting mixed aqueous solutions of either Mo, Ag, and I; Nb, Ag, and Ba; or Zr, Mo, Rh, Ag, Sn, I, and Ba, as well as a mixture of Ag and Ba nonradioactive microspheres. Mixtures containing 2-20 ppm of each element were counted for 10 min by the fluorescence system, and the individual elements in mixtures of three to seven nonradioactive elements were measured with high accuracy. The best counting statistics were obtained for Ag. For 10-min counts, the system measures as few as 120 Ag microspheres with 30% standard deviation but measures 800 Ag microspheres per sample with 3.6% standard deviation. We compared regional myocardial blood flows determined simultaneously by fluorescence and radioactive microsphere methods; the latter samples were counted by a 3-in. NaI (Tl) well detector and pulse-height analyzer. The radioactive and nonradioactive measurements showed good correlations.
Protective effects of 5-(N,N-dimethyl)amiloride on ischemia-reperfusion injury in hearts
Authors: Meng H. P. , Pierce G. N.
Published: December 2017

An Na(+)-H+ exchange inhibitor, 5-(N,N-dimethyl)amiloride (DMA), was used to probe the possible role of Na(+)-H+ exchange in ischemia-reperfusion injury in coronary perfused isolated rat right ventricular wall. In DMA-untreated hearts, 60 min of ischemia resulted in a significant rise in testing tension (RT: 174 +/- 8% of preischemic level). Thirty minutes of reperfusion further increased RT (273 +/- 12%) and induced a poor recovery in developed tension (DT: 28 +/- 4%). Both the rate of tension development and relaxation (+dT/dt and -dT/dt) recovered to a similar degree. When 1, 5, or 20 microM DMA was included in the perfusate (3 min before ischemia and in the first 3 min of reperfusion), the maximal postischemic RT of the heart was reduced to 204 +/- 21, 166 +/- 15, and 139 +/- 45% of the preischemic levels (P less than 0.05), respectively, and DT was 39 +/- 3, 63 +/- 10, and 79 +/- 8% of the preischemic levels (P less than 0.05), respectively. Similar qualitative recovery of +/- dT/dt was observed. Recovery was similar if DMA was present only during reperfusion. DMA treatment also significantly protected against creatine phosphokinase release during reperfusion. The results demonstrate that DMA can significantly protect the heart during the initial stages of reperfusion. The data suggest that Na(+)-H+ exchange may play an important role in the development of cardiac dysfunction and damage during the first minutes of reperfusion.
Stimulatory effect of ouabain on T- and L-type calcium currents in guinea pig cardiac myocytes
Authors: Le Grand B. , Deroubaix E. , Coulombe A. , Coraboeuf E.
Published: December 2017

The effect of 10(-6) M ouabain on macroscopic low-threshold T-type Ca2+ and high-threshold L-type Ca2+ currents was studied by whole cell recording in isolated guinea pig ventricular myocytes superfused with K-free, Na-free media, i.e., after suppression of Na-K-ATPase activity and Na influx through the Na-Ca exchanger. Under such conditions, the amplitudes of the two currents were significantly increased by ouabain. In particular, the current occurring in the -50 to -20 mV range (T-type Ca2+) was increased two- to threefold by ouabain and suppressed by 40 microM Ni2+. Ouabain shifted by approximately 10 mV toward negative potentials the steady-state inactivation curve of the T-type Ca2+ current but not that of the L-type Ca2+ current. It is concluded that ouabain enhances not only L-type Ca2+ current but also T-type Ca2+ current possibly through different mechanisms.
Purine metabolism after in vivo ischemia and reperfusion in rat skeletal muscle
Authors: Idstrom J. P. , Soussi B. , Elander A. , Bylund-Fellenius A. C.
Published: December 2017

An in vivo rat hindlimb tourniquet ischemia model was used to study the purine nucleotide metabolism in response to 2, 4, and 6 h of ischemia and to the same ischemia periods followed by 1 h of reperfusion. All purine intermediates from ATP to uric acid were determined in skeletal muscle with a high-performance liquid chromatography (HPLC) system. The major metabolic event during ischemia is to temporarily save the nucleotide pool as inosine-5'-monophosphate (IMP. On restitution of the circulation as the energy state recovers, the IMP is converted back to AMP via the purine nucleotide cycle. Six hours of ischemia is associated with irreversible damage and no recovery fo the adenine nucleotides on reperfusion. Fast-twitch muscles appear to be more susceptible than slow-twitch muscles in response to ischemia and reperfusion. A severalfold increase of intracellular hypoxanthine occurred during ischemia, whereas uric acid formation is observed only after reperfusion. These findings are discussed in relation to the proposed role of xanthine oxidase, as an enzyme generating tissue-injurious oxygen free radicals.
Stress-induced proteins in aortic smooth muscle cells and aorta of hypertensive rats
Authors: Kohane D. S. , Sarzani R. , Schwartz J. H. , Chobanian A. V. , Brecher P.
Published: December 2017

The current studies were performed to determine whether vascular smooth muscle cells produce stress-induced proteins when subjected to experimental hypertension. Two-dimensional gel electrophoresis was used to analyze labeled proteins in cultured cells in response to either heat shock or arsenite treatment. The major heat shock proteins (HSPs) induced had molecular masses of 70, 90, and 110 kDa. Arsenite treatment produced a similar response with the additional induction of a 30-kDa protein. In vitro translations of total RNA from heat-shocked cells, and RNA blot hybridization using HSP 70 cDNA suggested that HSP 70 induction was transcriptionally regulated. Treatment of cells with norepinephrine or angiotensin II induced cellular hypertrophy without eliciting HSPs. In vitro translation of aortic RNA from rats rendered hypertensive by administration of deoxycorticosterone and a high salt intake also did not reveal HSP induction. The absence of HSP induction using an in vivo model of hypertension suggests that those proteins may not be required to mediate the vascular response to experimental hypertension.
Power spectral analysis of heart rate variability in traumatic quadriplegic humans
Authors: Inoue K. , Miyake S. , Kumashiro M. , Ogata H. , Yoshimura O.
Published: December 2017

This study investigated the spontaneous beat-to-beat variabilities in R-R intervals of six traumatic neurologically complete quadriplegic (QP) males and six age-matched healthy males (control) while they were at rest in the supine position in a climatic chamber (temperature 30 degrees C, relative humidity 60%) by means of autoregressive power spectral analysis. As shown by earlier studies, in the control group there were two major spectral components, a high-frequency (HF) component [center frequency 0.30 +/- 0.02 (SE) Hertz equivalent (Hz eq), power 767.5 +/- 384.6 ms2] and a low-frequency (LF) component (0.11 +/- 0.01 Hz eq, 707.5 +/- 198.8 ms2). On the contrary, in the QP group, only the HF component was observed (0.30 +/- 0.02 Hz eq, 421.8 +/- 134.7 ms2). The results suggest that 1) the disappearance of the LF component in the QP subject is presumably caused by the interruption of the spinal pathways linking supraspinal cardiovascular centers with the peripheral sympathetic outflow, and 2) the cervical spinal sympathetic pathways may be instrumental in the genesis of the LF component in humans.
Normal responsiveness to external Ca and to Ca-channel modifying agents in hypertrophied rat heart
Authors: Callens-el Amrani F. , Mayoux E. , Mouas C. , Clapier-Ventura R. , Henzel D. , Charlemagne D. , Swynghedauw B.
Published: December 2017

In rat heart, the maximum velocity of shortening is decreased in response to chronic pressure overload. This is in part explained by an isomyosin shift, but several arguments suggest changes in membrane proteins. Inotropic response to calcium channel modifiers and to external calcium were simultaneously determined to explore this possibility. Left ventricular hypertrophy was induced by abdominal aortic stenosis and after 4-5 wk the left ventricular-to-body weight ratio increased by 61%. The effects of BAY K 8644 (10(-9) to 10(-6) M), a calcium channel activator, nifedipine (10(-9) to 10(-7) M), and external calcium (0.25-2.50 mM) were studied on isolated hearts at a coronary flow of 20 ml.min-1.g of left ventricle-1. The inotropic response (in percent changes in developed pressure and in dP/dtmax) was unmodified in the hypertrophied hearts. This work is in agreement with previous findings that both the total number of dihydropyridine binding sites and the peak magnitude of calcium current increase in proportion to the degree of hypertrophy. It suggests that the slowing of velocity could not be explained by a decreased number of Ca2+ channels but may more likely reflect modifications of the sarcomeres or sarcoplasmic reticulum.
Inositol 1,4,5-trisphosphate releases intracellular Ca2+ in permeabilized chick atria
Authors: Vites A. M. , Pappano A.
Published: December 2017

Inositol 1,4,5-trisphosphate (IP3) and caffeine evoked transient, reversible, and concentration-dependent increases in tension in saponin-treated chick atrial muscle. Contractures evoked by IP3 and caffeine were detected in solutions with 70 microM EGTA at pCa 7.0. In the presence of 7 mM EGTA, neither IP3 nor caffeine was able to evoke a contracture. Maximally effective concentrations of IP3 (20 microM) and caffeine (20 mM) developed tensions to approximately 44 and 83% of that elicited by pCa 5.0 (maximum tension = 100%), respectively. The IP3- or caffeine-induced contractures were consistently reproduced when the sarcoplasmic reticulum (SR) had previously been loaded with calcium. Preexposure to caffeine suppressed the following IP3-induced response. When ryanodine (1-10 microM) was present throughout the SR-loading cycle, the responses to IP3 and caffeine were prevented. However, when ryanodine was added after the SR was loaded with calcium, neither the response to IP3 nor that to caffeine was affected. These results are consistent with the hypothesis that ryanodine inhibition requires prior activation of the SR calcium-release channel. It is concluded that both IP3 and caffeine increased tension in the SR by releasing calcium from it. The effect of IP3 is consistent with its messenger role as a calcium-mobilizing agent.
Mechanisms underlying early and delayed afterdepolarizations induced by catecholamines
Authors: Priori S. G. , Corr P. B.
Published: December 2017

The relative influence of alpha- and beta-adrenergic receptor activation in eliciting early (EADs) and delayed (DADs) after depolarizations was assessed using intracellular microelectrode recordings in isolated adult canine ventricular myocytes. Normoxic myocytes were exposed to the alpha-adrenergic agonist phenylephrine (10(-8)-10(-6) M) or the beta-adrenergic agonist isoproterenol (10(-9)-10(-6) M) during pacing at different frequencies (0.5-4 Hz). alpha-Adrenergic stimulation resulted in a dose-dependent prolongation of action potential duration but failed to induce either EADs or DADs. beta-Adrenergic stimulation with isoproterenol at low concentrations (10(-9)-10(-8) M) induced a prolongation of the action potential, whereas higher concentrations (10(-7) and 10(-6) M) resulted in a marked shortening. Isoproterenol elicited single or multiple (2-5) DADs at concentrations from 10(-8) to 10(-6) M, with a corresponding increase in the amplitude of the DADs and decrease in the coupling interval as cells were paced at increasing rates. DADs often initiated and maintained sustained triggered rhythms that spontaneously terminated. Isoproterenol (10(-8)-10(-6) M) also elicited EADs in 80% of cells at the highest concentration utilized (10(-6) M) and at intermediate pacing frequencies (1-2 Hz). EADs often occurred with a 2:1 or 3:1 pattern. EADs and DADs induced by isoproterenol were reversibly abolished by low extracellular sodium, ryanodine (10(-6) M), or benzamil (10(-4) M), thus indicating that Ca2+ release from the sarcoplasmic reticulum and extracellular Na+ concentration are two major factors in the development of both types of afterdepolarizations. The demonstration that EADs can be induced by isoproterenol in ventricular muscle suggest a novel pathway for beta-adrenergic receptors to mediate arrhythmogenesis in the intact heart.
Functional and metabolic responses of isolated hearts to acidosis: effects of sodium bicarbonate and Carbicarb
Authors: Shapiro J. I.
Published: December 2017

To investigate the mechanisms by which acidosis depresses cardiac function, a Langendorff isolated, perfused rat heart preparation was studied using 31P-magnetic resonance spectroscopy. Isolated hearts were subjected to normal perfusion conditions or moderate or severe metabolic acidosis. Acidosis resulted in dose-dependent decreases in O2 consumption (VO2), rate of developed ventricular pressure (dP/dt), intracellular pH (pHi), and the tissue concentration of creatine phosphate (PCr) after 30 min. Acidosis did not affect ATP concentration but resulted in significant increases in the concentrations of total and monovalent inorganic phosphate (Pi and Pim). When metabolic determinants of the change in dP/dt with acidosis were examined, changes in pHi, extracellular pH, and tissue concentrations of Pi and Pim all correlated significantly with the change in dP/dt. In a second set of experiments using the severe acidosis model, normal saline, 1 M sodium bicarbonate, and the experimental buffer Carbicarb (1 ml/kg body wt) were infused in a crossover manner at 20-min intervals. None had significant effects on tissue concentrations of ATP, PCr, Pi, or PCr/Pi. Administration of bicarbonate resulted in an increase in VO2 without significant effects on pHi or dP/dt. In contrast, Carbicarb effected little change in VO2 but resulted in sustained increases in pHi and decreases in Pim and marked increases in dP/dt. These data suggest that the decrease in cardiac function that occurs during acidosis may be related to the metabolic consequences of reductions in pHi and that a buffer that causes intracellular alkalinization may cause functional improvement in this model.
Angiotensin II induces endothelium-dependent vasodilation of rat cerebral arterioles
Authors: Haberl R. L. , Anneser F. , Villringer A. , Einhaupl K. M.
Published: December 2017

We evaluated the response of cerebral arterioles to angiotensin II (ANG II) in anesthetized rats equipped with a closed cranial window. Topical application of 10(-10)-10(-5) M ANG II induced dose-dependent arteriolar vasodilation. Maximum vasodilation of 24 +/- 2.2% (+/- SE) was attained at a concentration of 10(-6) M ANG II. The dilation in response to ANG II was blocked by 3 micrograms/ml indomethacin, a cyclooxygenase inhibitor, and was reversed to minimal vasoconstriction by 10(-5) M methylene blue, a substance that has been reported to eliminate endothelium-dependent vasodilation. Coapplication of indomethacin with methylene blue reduced the arteriolar response to ANG II to a similar extent as the application of indomethacin alone. Indomethacin or methylene blue did not inhibit the vasodilation induced by 10(-5) M adenosine, which is not endothelium and cyclooxygenase dependent. Mercury light illumination of the pial vessels after intravenous injection of fluorescein dye, a technique that has been used by others to functionally damage endothelial cells, reversed ANG II (10(-6) M)-induced vasodilation into a -14.2 +/- 2.3% constriction while not affecting the response to adenosine. Our data suggest that ANG II produces vasodilator responses of rat cerebral arterioles by the release of a factor that is derived from the endothelium and may be generated through a cyclooxygenase-dependent mechanism.
Polymorphonuclear leukocytes reduce cardiac function in vitro by release of H2O2
Authors: Kraemer R. , Seligmann B. , Mullane K. M.
Published: December 2017

Polymorphonuclear leukocytes (PMNs) have been implicated in postischemic myocardial injury and associated derangements in contractile function. To examine the direct effects of PMNs on cardiac function, isolated right ventricular papillary muscles of the rabbit were exposed to increasing concentrations of purified rabbit PMNs in the presence of cimetidine. PMNs induced a significant concentration-dependent decrease in contractile function, where 5 x 10(5) PMNs/ml reduced contractile force to 75 +/- 2.1% of control (vs. 95 +/- 5% for time control; P less than 0.005). Similar decreases were also observed for peak positive and negative first derivatives of contractile force. The degree of PMN-induced contractile dysfunction correlated with the activity of the PMNs in an aggregation assay (r = 0.82, P less than 0.01). The loss of contractile function in response to PMNs was attenuated by catalase, which metabolizes H2O2, but not by superoxide dismutase, a scavenger of the superoxide anion. PMNs can convert H2O2 to either the hypochlorite anion or the hydroxyl radical, which are removed by methionine or mannitol, respectively. However, these scavengers did not ameliorate the PMN-induced loss of cardiac function. Exposure of papillary muscles to H2O2 resulted in a concentration-dependent decrease in contractile function where 100 microM reduced contractile force to 78 +/- 4%, an effect prevented by catalase. Thus PMNs reduce the contractile function of isolated papillary muscles probably by the release of H2O2.
Does volume catheter parallel conductance vary during a cardiac cycle?
Authors: Lankford E. B. , Kass D. A. , Maughan W. L. , Shoukas A. A.
Published: December 2017

Absolute left ventricular volume measurement by the conductance (volume) catheter requires subtraction of the conductance contribution from structures extrinsic to the cavity blood pool. Previously, this parallel conductance volume (Vp) has been assumed constant throughout the cardiac cycle, and the technique described for its estimation in situ yields a single value. We present a new method for parallel conductance determination that yields multiple estimates during systole, enabling an assessment of Vp variability [Vp(t)]. For isolated blood-perfused ejecting canine left ventricles with empty (vented) right ventricles, Vp(t) displayed virtually no variation throughout systole. For in situ hearts, despite the presence of other cardiac chambers, Vp(t) also displayed little variation, with no statistically significant deviation from its mean value throughout systole. Volume signal simulations found the new technique to be less sensitive to signal noise and thus more robust than the one previously published. The isolated and in situ heart data indicate that for the left ventricle, the parallel conductance is relatively constant throughout normal ejection.
Analysis of capillary geometry in rat subepicardium and subendocardium
Authors: Poole D. C. , Mathieu-Costello O.
Published: December 2017

The sustained high-energy turnover of cardiac muscle presents a formidable challenge to the O2 delivery systems. One major determinant of blood-tissue gas exchange potential is capillary surface area per volume of muscle fiber, Sv(c,f). Estimation of Sv(c,f) necessitates quantification of capillary orientation. Capillary geometry was analyzed systematically in subepi- (epi) and subendocardium (endo) of glutaraldehyde perfusion-fixed rat heart (n = 4). On 1-micron sections cut rigorously transverse and longitudinal to the muscle fiber axis we determined capillary number per fiber square millimeter on transverse, QA(0), and longitudinal, QA(pi/2), sections, capillary diameter, d(c), fiber cross-sectional area, a(f), and sarcomere length, l. Sv(c,f) was computed as pi.d(c).Jv(c,f), where Jv(c,f) is capillary length per fiber volume determined on the basis of a directional distribution model of capillary segments (Fisher axial). Analysis of capillary density, QA(alpha), in sections taken at angles alpha [from 0 to 90 degrees (pi/2) to fiber axis] showed that the Fisher axial distribution provides a good fit to capillary segment orientation in cardiac muscle. No systematic difference was found in fiber size (epi = 269.7 +/- 28.9, endo = 283.8 +/- 16.3 microns 2), capillary diameter (epi = 4.9 +/- 0.3; endo = 4.5 +/- 0.2 microns), Jv(c,f) (epi = 6,302 +/- 558; endo = 5,957 +/- 492 mm-2), or capillary surface per volume of muscle fiber (epi = 968.1 +/- 76.5; endo = 838.2 +/- 93.0 cm-1) between epi and endo. Contribution of capillary tortuosity and branching to Jv(c,f) ranged from 6-27% (epi) and 8-21% (endo) over the small ranges of l considered (epi = 2.09-2.23; endo = 2.04-2.17 microns).(ABSTRACT TRUNCATED AT 250 WORDS)
Membrane-delimited stimulation of heart cell calcium current by beta-adrenergic signal-transducing Gs protein
Authors: Pelzer S. , Shuba Y. M. , Asai T. , Codina J. , Birnbaumer L. , McDonald T. F. , Pelzer D.
Published: December 2017

A severalfold increase in calcium current (ICa) is a signal feature of the maximal beta-adrenergic response of the heart. It is generally ascribed to enhanced adenosine 3',5'-cyclic monophosphate (cAMP)-dependent phosphorylation of calcium (Ca) channels after beta-receptor activation of the guanosine nucleotide-binding (G) protein Gs, and Gs activation of the adenylyl cyclase cascade. We blocked phosphorylation pathways in guinea pig cardiomyocytes to unmask other possible ICa-stimulatory modes. In blocked cells, ICa increased by approximately 50% during 1) beta-receptor activation of Gs, 2) intracellular activation of Gs, and 3) intracellular application of preactivated Gs, We conclude that fast, membrane-delimited Gs modulation participates in the physiological regulation of cardiac ICa.
Smooth muscles from spastic coronary artery segments show hypercontractility to histamine
Authors: Satoh S. , Tomoike H. , Mitsuoka W. , Egashira S. , Tagawa H. , Kuga T. , Nakamura M.
Published: December 2017

An animal model of coronary spasm was produced in Gottingen miniature pigs by a selective endothelial denudation of the coronary artery. Five months after the denudation, intracoronary bolus administration of 10 micrograms/kg histamine reduced the luminal diameter angiographically by 57 +/- 16 and 17 +/- 10% (P less than 0.01) in the previously denuded and contralateral control coronary arteries. Muscle fibers of 0.08–0.1 mm wide were prepared from circumferential bundles of the medial smooth muscle in the spastic and nonspastic coronary arteries. Upward shifts of either dose-tonic contraction relationships in Ca2(+)-containing solution or dose-monophasic contraction relationships in Ca2(+)-free solution were noted in muscle fibers taken from the spastic site compared with those from the nonspastic site with no difference between the mean effective dose values. After skinning the muscle fibers with saponin, there was no significant difference in the Ca2+ concentration-tension relationships between the two fibers. These findings suggest that an increased number of histaminergic receptors and/or augmentation of signal transduction, but not Ca2+ sensitivity of the contractile proteins in the medial smooth muscle cells, cause histamine-induced coronary hypercontraction.
Renin-angiotensin system involvement in pressure-overload cardiac hypertrophy in rats
Authors: Baker K. M. , Chernin M. I. , Wixson S. K. , Aceto J. F.
Published: December 2017

We have recently shown that the octapeptide angiotensin II is a potent stimulus of protein synthesis and growth in cultured cardiomyocytes. The present study was performed to determine if the renin-angiotensin system was involved in regulating cardiac cell growth in vivo. The pressure-overload cardiac hypertrophy model that develops in abdominal aorta-constricted rats was studied. At 7 and 15 days after abdominal aorta constriction, rats developed significant left ventricular hypertrophy. The increase in left ventricular mass was completely prevented in animals fed the angiotensin-converting enzyme inhibitor, enalapril maleate (0.2 mg/ml) in their drinking water. Cardiac afterload was the same in both groups of animals in that carotid artery pressures were not different in conscious awake aortic-constricted animals receiving and not receiving enalapril. These data suggest a direct growth effect of angiotensin II on the left ventricle and indicate a role for the renin-angiotensin system in the cardiac hypertrophy that develops in response to pressure overload. The presence and chamber localization of angiotensinogen mRNA was determined using Northern hybridization and S1 nuclease mapping analysis. Angiotensinogen mRNA, as determined by dot-blot hybridization analysis, was significantly increased in hypertrophied left ventricles at both 7 and 15 days after the surgery, when compared with sham-operated controls. The activity of the circulating renin-angiotensin system, as indexed by plasma renin activity was increased at 1 day following surgery [6.0 +/- 2.0 ng.ml-1.h-1 angiotensin I (control) vs. 41.8 +/- 10.9 ng.ml-1.h-1 angiotensin I (experimental)], but returned to control values by day 3 postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)
Influence of Na+ gradient on Ca2+ transients and contraction in vascular smooth muscle
Authors: Bova S. , Goldman W. F. , Yauan X. J. , Blaustein M. P.
Published: December 2017

The effects of reducing external Na+ ([Na+]o) and increasing internal Na+ ([Na+]i) on evoked tension in arterial rings were correlated with intracellular Ca2+ transients evoked in cultured A7r5 cells. Contractions were elicited in rings of rat aorta and a small mesenteric artery branch by serotonin (5-HT), arginine vasopressin (AVP), or a high K+ concentration ([K+]o). Contractions were augmented by reduction of [Na+]o (replaced by Li+ or N-methylglucamine) or inhibition of the Na+ pump (to raise [Na+]i). These effects were dependent on external Ca2+. Ca2+ transients were measured by digital imaging of fura-2/AM-loaded A7r5 cells. The apparent free Ca2+ concentration [( Ca2+]app) in eight unstimulated cells was 110 +/- 10 nM in the peripheral cytoplasm. Activation of A7r5 cells by 5-HT, AVP, or high [K+]o evoked transient increases in [Ca2+]app. Lowering [Na+]o or raising [Na+]i elevated [Ca2+]app significantly in unstimulated cells and increased the amplitude and duration of the Ca2+ transients. These effects required external Ca2+. Caffeine (5-10 mM) reduced [Ca2+]app in resting cells and attenuated the vasoconstrictor-evoked Ca2+ transients in low [Na+]o. The data imply that Na+ gradient reduction promotes Ca2+ entry and slows Ca2+ extrusion via Na(+)-Ca2+ exchange. This increases cytosolic free Ca2+ and the intracellular Ca2+ stores so that more Ca2+ is delivered to the contractile apparatus during cell activation. Such augmented Ca2+ transients could induce the amplified vasoconstrictor-evoked contractions observed in arterial rings under reduced Na+ gradient conditions.
Effect of endothelial cell denudation on fatty acid metabolism by rabbit aorta
Authors: Takasaki I. , Cohen R. A. , Chobanian A. V. , Brecher P.
Published: December 2017

The potential regulatory role of vascular endothelial cells in fatty acid uptake and metabolism by arterial tissue was studied in vitro using aortic segments from New Zealand White rabbits. Endothelium was left intact or was removed either by scraping with forceps or by rubbing with a cotton swab. Aortic segments were incubated with [14C]oleate or [14C]arachidonate, and oxidation and esterification were measured. Endothelial cell denudation by forceps or cotton swab caused a decrease in oxidation of both oleic and arachidonic acid. Esterification of oleic and arachidonic acid into phospholipid was also significantly reduced by removing the endothelium; the percent reduction was less when endothelium was removed by cotton swab than it was by forceps. Incorporation into phospholipid was reduced by cotton swab treatment, but incorporation into triglyceride was unaffected. Forceps treatment reduced oleic acid esterification into both triglyceride and phospholipid. The studies suggest that arterial endothelium has a role in fatty acid oxidation and esterification and that fatty acid utilization may be a useful metabolic index of vascular injury.