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  • 1
    Electronic Resource
    Electronic Resource
    Interactions between coronary occlusion and the renin-angiotensin system in the dog (1983)
    Springer
    Basic research in cardiology 78 (1983), S. 518-533 
    Details
    ISSN: 1435-1803
    Keywords: renin ; angiotensin ; coronary artery occlusion ; myocardial ischemia ; Captopril ; Saralasin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Studies were carried out in 39 barbiturate-anesthetized dogs to determine whether the renin-angiotensin system is important in control of hemodynamics and coronary flow during myocardial ischemia. Plasma renin activity (PRA) was 2.2±0.4 ng·ml−1·hr−1 immediately before coronary artery occlusion (CAO) and increased to 3.8±0.5 (p〈.005) 15 minutes after CAO. In nephrectomized dogs, PRA was 0.76±0.14 ng·ml−1·hr−1 two hours after nephrectomy and remained unchanged after CAO. In contrast, hemodynamic changes following CAO were similar between nephrectomized and intact dogs: mean arterial pressure fell from 126±4 pre CAO to 116±4 mm Hg post CAO (p〈0.005) in nephrectomized dogs and from 130±11 to 120±11 mm Hg (p〈0.005) in intact dogs. Left atrial pressure rose from 5.4±0.9 pre CAO to 7.7±0.9 mm Hg (p〈0.005) post CAO in nephrectomized dogs and 6.3±1.3 to 9.0±1.8 mm Hg (p〈0.005) in intact dogs. Heart rate remained unchanged in both groups. In sham-operated dogs without CAO, neither the angiotensin II blocker Saralasin nor the converting enzyme inhibitor Captopril had significant effects on systemic (SVR) and coronary (CVR) vascular resistances. In contrast, in dogs with CAO, these drugs reduced CVR from 1.28±0.13 mm Hg·ml−1·min·100 g heart weight (resistance units=RU) to 0.85±0.08 RU (p〈0.05) (Saralasin) 15 minutes after treatment and from 1.17±0.09 to 0.88±0.08 RU (p〈0.025), (Captopril) respectively. However, only Captopril reduced SVR, from 10.7±1.13 to 8.2±0.8 RU (p〈0.025). Both Captopril and Saralasin induced a significant increase in collateral blood flow. Nephrectomy, two hours prior to CAO, significantly reduced the effect of Captopril on CVR and collateral blood flow while the effect on SVR persisted. Thus the reduction in CVR appears to be an effect of inhibition of the renin-angiotensin system; this system participates in control of CVR during CAO and may limit coronary collateral blood flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01906463
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  • 2
    Electronic Resource
    Electronic Resource
    The reduction of NO with H2 over Ru/MgO (1998)
    Springer
    Catalysis letters 53 (1998), S. 77-81 
    Details
    ISSN: 1572-879X
    Keywords: SCR of NO ; Ru ; MgO ; frontal chromatography ; TPD ; TPSR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ruthenium supported on magnesia was found to be a highly active and selective catalyst for the reduction of NO to N2 with H2. The adsorption of NO on Ru/MgO was studied at room temperature by applying frontal chromatography with a mixture of 2610 ppm NO in He. Subsequently, temperature‐programmed desorption (TPD) and temperature‐programmed surface reaction (TPSR) experiments in H2 were performed. The adsorption of NO was observed to occur partly dissociatively as indicated by the formation of molecular nitrogen. The TPD spectrum exhibited a minor NO peak at 340 K indicating additional molecular adsorption of NO during the exposure to NO at room temperature, and two N2 peaks at 480 K and 625 K, respectively. The latter data are in good agreement with previous results with Ru(0001) single‐crystal samples, where the interaction with NH3 was found to lead to two N2 thermal desorption states with a maximum coverage of atomic nitrogen of about 0.38. Heating up the catalyst after saturation with NO at room temperature in a H2 atmosphere revealed the self‐accelerated formation of NH3 after partial desorption of N2, whereby sites for reaction with H2 become available. As a consequence, the observed high selectivity towards N2 under steady‐state reduction conditions is ascribed to the presence of a saturated N+O coadsorbate layer resulting in an enhanced rate of N2 desorption from this layer and a very low steady‐state coverage of atomic hydrogen. The formation of H2O by reduction of adsorbed atomic oxygen is the slow step of the overall reaction which determines the minimum temperature required for full conversion of NO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019072915187
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  • 3
    Electronic Resource
    Electronic Resource
    The temperature-programmed desorption of N2 from a Ru/MgO catalyst used for ammonia synthesis (1996)
    Springer
    Catalysis letters 36 (1996), S. 229-235 
    Details
    ISSN: 1572-879X
    Keywords: N2 TPD ; N2 adsorption ; Ru ; MgO ; NH3 synthesis ; microkinetic analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The temperature-programmed desorption (TPD) of N2 from a Ru/MgO catalyst used for ammonia synthesis was studied in a microreactor flow system operating at atmospheric pressure. Saturation with chemisorbed atomic nitrogen (N-*) was achieved by exposure to N2 at 573 K for 14 h and subsequent cooling in N2 to room temperature. With a heating rate of 5 K/min in He, a narrow and fairly symmetric N2 TPD peak at about 640 K results. From experiments with varying heating rates a preexponential factor Ades = 1.5×1010 molecules/(site s) and an activation energy Edes = 158 kJ/mol was derived assuming secondorder desorption. This rate constant of desorption is in good agreement with results obtained with a Ru(0001) single crystal surface in ultra-high vacuum (UHV). The rate of dissociative chemisorption was determined by varying the N2 exposure conditions. Determination of the coverage of N-* was based on the integration of the subsequently recorded N2 TPD traces yielding Aads = 2×10−6 (Pa s)−1 and Eads = 27 kJ/mol. The corresponding sticking coefficient of about 10−14 at 300 K is in agreement with the inertness of Ru(0001) in UHV towards dissociative chemisorption of N2. However, if the whole catalytic surface were in this state, then the resulting rate of N2 dissociation would be several orders of magnitude lower than the observed rate of NH3 formation. Hence only a small fraction of the total Rumetal surface area of Ru/MgO seems to be highly active dominating the rate of ammonia formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807624
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  • 4
    Electronic Resource
    Electronic Resource
    The dissociative adsorption of N2 on a multiply promoted iron catalyst used for ammonia synthesis: a temperature-programmed desorption study (1994)
    Springer
    Catalysis letters 24 (1994), S. 317-331 
    Details
    ISSN: 1572-879X
    Keywords: Nitrogen adsorption ; N2 TPD ; iron-based catalyst ; ammonia synthesis ; microkinetic analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The temperature-programmed desorption (TPD) of N2 from a multiply promoted iron catalyst used for ammonia synthesis has been studied in a microreactor system at atmospheric pressure. From TPD experiments with various heating rates a preexponential factorA = 2 × 109 molecules/site s and an activation energyE = 146 kJ/mol was derived assuming second-order desorption. The observed dependence of the TPD peak shapes on the heating rates indicated the influence of readsorption of N2 in agreement with the results obtained for various initial coverages. Simulating the N2 TPD curves using the model by Stoltze and Nørskov revealed that the calculated TPD curves were not influenced by the molecular precursor to desorption. However, the calculated rate of readsorption was found to be overestimated at high coverage compared with the experimental results. A coverage-dependent net activation energy for dissociative chemisorption (E*) was introduced as the simplest assumption rendering the dissociative chemisorption of N2 activated at high coverage. The best fit of the experimental data yieldedE* = (−15+30θ) kJ/mol using only a single type of atomic nitrogen species. These findings are in satisfactory agreement with the parameters underlying the Stoltze-Nørskov model for the kinetics of ammonia synthesis as well as with the data reported for Fe(111) single crystal surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811804
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  • 5
    Electronic Resource
    Electronic Resource
    Deterioration of metabolic coronary regulation in hemorrhagic shock (1985)
    Springer
    Research in experimental medicine 185 (1985), S. 429-443 
    Details
    ISSN: 1433-8580
    Keywords: Myocardial blood flow ; Angiotensin II ; Saralasin ; Nephrectomy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of hypoxia and the renin-angiotensin system on metabolic coronary regulation in hemorrhagic shock was studied in 22 anesthetized open-chest dogs. Left circumflex coronary blood flow was measured with an electromagnetic flowmeter. Dogs were ventilated with room air (n = 8) or 100% oxygen (n = 7). A third group of dogs was ventilated with room air and bilaterally nephrectomized 5 h prior to starting the experimental protocol (n = 7). After control data had been obtained, dogs were bled from the femoral arteries into a pressurized reservoir which maintained blood pressure at 45 ± 1 mm Hg. The angiotensin II receptor blocker, saralasin, was then infused i.v. (0.1, 1.0, 10.0 µg/kg per min). Coronary blood flow was reduced by hemorrhage, and no significant difference existed in coronary flow during hemorrhage among the three groups. Coronary sinus oxygen saturation was diminished in control animals during hemorrhage from 26% ± 1% to 17% ± 1% (P 〈 0.05) but normal in 100% oxygen ventilated animals (30% ± 3%) and in nephrectomized dogs (34% ± 4%). Coronary oxygen extraction was reduced by saralasin in intact but not in nephrectomized dogs. In six additional experiments, in which blood pressure was not artificially held constant during saralasin infusion, saralasin still significantly improved coronary sinus oxygen saturation and thus reduced coronary oxygen extraction. The data suggest that both hypoxia and the reninangiotensin system participate in the restriction of metabolic coronary regulation in hemorrhagic shock.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01851849
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