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  • 1
    Electronic Resource
    Electronic Resource
    Ro 22-9194: A New Class I Antiarrhythmic Agent (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Cardiovascular drug reviews 14 (1996), S. 0 
    Details
    ISSN: 1527-3466
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1527-3466.1996.tb00313.x
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  • 2
    Electronic Resource
    Electronic Resource
    Autonomic Control of the Location and Rate of the Cardiac Pacemaker in the Sinoatrial Fat Pad of Parasympathetically Denervated Dog Hearts (2002)
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 13 (2002), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Autonomic Regulation of Pacemaker Sites. Introduction: Parasympathetic activity predominates over sympathetic activity not only with respect to heart rate but also with respect to the pacemaker location in the dog heart. After we removed the parasympathetic neural elements in the sinoatrial (SA) fat pad in the right atrium, we observed that cervical vagus stimulation did not decrease the atrial rate, but it did suppress the increase in rate evoked by sympathetic stimulation. We determined whether the pacemaker rate and location were affected by presynaptic or postsynaptic mechanisms. Methods and Results: We determined the earliest activation site by means of isochronic activation mapping of the right atrium of open chest, anesthetized dog hearts. An electrode array, which consisted of 48 unipolar electrodes, was used to record atrial activation. This array covered the three main pacemaker regions, including the SA node region. After parasympathetic nerve fibers in the SA fat pad had been denervated, vagus stimulation at 10 and 30 Hz did not decrease the heart rate, but it attenuated the increase in heart rate evoked by sympathetic stimulation or isoproterenol. Vagus stimulation at 10 Hz during sympathetic stimulation did not shift the earliest activation site from the superior pacemaker region to the SA node region in 11 of 18 experiments. However, vagus stimulation at 10 Hz during isoproterenol infusion shifted the earliest activation site to the SA node region in 11 of 13 experiments. More intense vagus stimulation during combined sympathetic stimulation or isoproterenol infusion shifted the earliest activation site to the SA node or the inferior pacemaker region in 15 of 18 and in all experiments, respectively. Conclusion: The results suggest that activation of parasympathetic elements not located in the SA fat pad attenuates the increase in heart rate and the shift in pacemaker location evoked by sympathetic activation. The sympathetic and parasympathetic effects interact at presynaptic and postsynaptic sites in the dog heart.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2002.00896.x
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanism for Atrial Tachyarrhythmia in Chronic Volume Overload-Induced Dilated Atria (2005)
    350 Main Street , Malden , MA 02148-5018 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 16 (2005), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Introduction: Atrial dilatation associated with chronic volume overload (CVO) plays an important role in the development of atrial fibrillation (AF). However, the underlying mechanisms are unknown. Methods and Results: CVO-induced atrial dilatation was created in Japanese white rabbits using arteriovenous shunt formation for 6 weeks. Epicardial action potentials were measured from both atria in Langendorff-perfused sham-operated control hearts (n = 8) and in CVO hearts (n = 8) using high-resolution optical mapping techniques. The left atrial diameter was greater in CVO hearts (16.0 ± 0.4 mm) compared to control hearts (11.0 ± 0.8 mm). During steady-state pacing, right and left atrial conduction velocities were significantly lower in CVO hearts compared to control hearts (P 〈 0.01). Rapid atrial pacing did not induce atrial tachyarrhythmia (AT) in any control hearts. However, in seven of eight CVO hearts 16 episodes of AT were induced, of which 9 exhibited a single reentrant circuit. The remaining 7 episodes exhibited a focal pattern of excitation without evidence of reentry. Interestingly, the activation rate was higher during reentry (16.1 ± 1.5 Hz) compared to focal AT (9.8 ± 1.0 Hz). In addition, 15 of 16 episodes occurred in the posterior left atrium (PLA). In all seven CVO hearts, AT was self-sustained for more than 10 minutes. Conclusion: CVO caused atrial dilatation, conduction slowing, and AT associated with reentrant and focal excitation originating from the PLA. These results suggest that the PLA may play an important role in AT induction associated with CVO-induced atrial dilation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2005.40331.x
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  • 4
    Electronic Resource
    Electronic Resource
    Parasympathetic Inhibition of Sympathetic Effects on Pacemaker Location and Rate in Hearts of Anesthetized Dogs (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 10 (1999), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Autonomic Effect on Pacemaker Location. introduction: The site of impulse origin in the right atrium generally is considered to be a single static locus within the sinoatrial (SA) node. Previous investigators showed that the pacemaker site may shift due to changes in sympathetic or parasympathetic neural activity. We investigated the interactions between sympathetic and parasympathetic influences on the site of impulse initiation in the right atrium in anesthetized dogs. Methods and Results: We determined the site of impulse initiation and the spread of excitation over the anterior and posterior regions of the right atrium by a matrix of 48 unipolar recording electrodes. We assessed the spread of excitation at 3-nisec intervals by constructing isochronal activation sequence maps. Sympathetic stimulation increased the frequency of atrial excitation (i.e., the heart rate), but also shifted the earliest activation region (EAR) from a locus in the SA node to a locus in the superior vena cava (the superior pacemaker site). Vagus stimulation decreased the heart rate and shifted the EAR to a lower site in the SA node or a site in the interior right atrium along the sulcus terminalis (the inferior pacemaker site). A short period of vagus stimulation during a more prolonged sympathetic stimulation elicited a larger decrease in rate than did vagus stimulation alone and shifted the EAR from the superior site to the SA node or to the inferior site. After atropine, combined stimulation shifted the EAR to the superior site, but propranolol did not change EAR location. Conclusion: Our results suggest that parasympathetic activity predominates over sympathetic activity not only on heart rate, but also on the location of the EAR in the anesthetized dog.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8167.1999.tb00279.x
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  • 5
    Electronic Resource
    Electronic Resource
    ZATEBRADINE ATTENUATES CYCLIC AMP-RELATED POSITIVE CHRONOTROPIC BUT NOT INOTROPIC RESPONSES IN ISOLATED, PERFUSED RIGHT ATRIA OF THE DOG (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Clinical and experimental pharmacology and physiology 22 (1995), S. 0 
    Details
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. Inhibition of If or Ica by zatebradine has been reported in mammalian SA nodal cells. We thus investigated whether zatebradine differentially attenuates the positive chronotropic and inotropic responses to norepinephrine, isoproterenol, NKH 477 (an adenylyl cyclase activator), 3-isobutyl-1-methylxanthine (IBMX) and Bay k 8644 (a calcium channel agonist) in the isolated, blood-perfused dog atrium.2. When zatebradine (0.03–1 μmol) decreased sinus rate from 104 ± 4.5 to 73 ± 4.9 beats/min dose-dependently, it selectively attenuated the positive chronotropic but not inotropic responses to norepinephrine in a dose-related manner. Zatebradine decreased the norepinephrine-induced tachycardia (by approximately 80% from the control) more effectively than the spontaneous sinus rate (by approximately 30% from the control).3. Zatebradine similarly attenuated the positive chronotropic but not inotropic responses to isoproterenol, NKH 477 and IBMX. Fifty per cent inhibition doses of zatebradine (0.10–0.18 μmol) for the chronotropic responses to each substance were not significantly different.4. On the other hand, zatebradine attenuated neither positive chronotropic nor inotropic responses to Bay k 8644.5. We therefore suggest that zatebradine selectively attenuates the positive chronotropic but not inotropic responses to cyclic AMP-related substances due to inhibition of If but not Ica in the dog heart.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1681.1995.tb01914.x
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  • 6
    Electronic Resource
    Electronic Resource
    Cellular mechanism of pituitary adenylate cyclase-activating polypeptide-induced atrial tachyarrhythmia in canine isolated arterially perfused right atria (2003)
    Oxford, UK : Blackwell Science Pty
    Clinical and experimental pharmacology and physiology 30 (2003), S. 0 
    Details
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. Pituitary adenylate cyclase-activating polypeptide (PACAP) induces atrial tachyarrhythmia (AT). However, the cellular mechanism responsible for this remains unclear.2. In six canine isolated arterially perfused right atria, high-resolution optical mapping techniques were used to measure action potentials during control conditions and after PACAP injection (1 nmol).3. During steady state pacing at a cycle length of 300 msec, the action potential duration was shorter during PACAP than during control (P 〈 0.001). In addition, maximum repolarization gradients during PACAP (4 ± 1 msec/mm) were similar to those during control (5 ± 1 msec/mm; n = 6). Transmural repolarization gradients were also similar between the two groups.4. After PACAP, AT was easily initiated with a single premature extrastimulus and was associated with a focal pattern of activation. However, AT was not initiated by a single premature stimulus during control.5. In conclusion, the PACAP-induced AT is associated with a focal pattern of activation that is independent of local repolarization gradients. These data suggest that increased dispersion of repolarization is not necessarily required for the induction of AT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1681.2003.03940.x
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  • 7
    Electronic Resource
    Electronic Resource
    BRADYKININ-INDUCED VASCULAR RESPONSES IN DOG ISOLATED LINGUAL ARTERY (1999)
    Melbourne, Australia : Blackwell Science Pty
    Clinical and experimental pharmacology and physiology 26 (1999), S. 0 
    Details
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. Kinin-induced vascular responses were studied and kinin receptor subtypes were characterized in canine isolated and preconstricted lingual arteries.2. A low dose of bradykinin (BK; 〈 3 × 10–14 mol) induced only vasodilation, while a higher dose of BK (〉 3 × 10–13 mol) frequently induced a biphasic response: a transient constriction followed by dilation.3. The BK-induced vasodilation was mostly endothelium dependent but was also partly endothelium independent because although the dilation response was greatly reduced after removal of the endothelium, it was not completely abolished.4. The dilation response to BK was significantly inhibited by the B2 kinin receptor antagonist HOE 140 and was partly reduced by indomethacin (10 μmol/L) (P 〈 0.05).5. Bradykinin-induced vasoconstriction was enhanced in endothelium-denuded preparations. The constriction was significantly inhibited by HOE 140 (10–10 mol/L). The BK-induced responses were not affected by the B1 kinin receptor antagonist des-Arg9-[Leu8]-BK (3 × 10–11 mol/L).6. The B1 kinin receptor agonist des-Arg9-BK (〉 10–12 mol/L) produced vasodilation in 60% of endothelium-intact preparations. In 20% of the endothelium-intact preparations des-Arg9-BK produced a biphasic response: weak vasoconstriction followed by weak vasodilation. The des-Arg9-BK-induced dilation and constriction were significantly inhibited by des-Arg9-[Leu8]-BK (3 × 10–11 mol/L), but were not affected by HOE 140 (10–10 mol/L).7. In conclusion, it appears that both B1 and B2 kinin receptors are present in the dog lingual artery. Both receptor subtypes mediate either vasodilation or vasoconstriction and BK-induced vasodilation is mostly endothelium dependent, although it may also be partially prostaglandin dependent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1440-1681.1999.03057.x
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  • 8
    Electronic Resource
    Electronic Resource
    CEREBROVASCULAR CONTRACTILITY AFTER CLOT REMOVAL IN MONKEY SUBARACHNOID HAEMORRHAGE (1999)
    Melbourne, Australia : Blackwell Science Pty
    Clinical and experimental pharmacology and physiology 26 (1999), S. 0 
    Details
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The effects of mechanical clot removal during early surgery on pharmacological cerebrovascular reactivity after subarachnoid haemorrhage (SAH) were investigated in the monkey.2. Contractions to potassium chloride, 5-hydroxytryptamine and noradrenaline in rings of proximal parts of middle cerebral arteries (MCP), surrounded with clot, and basilar arteries (BAP), far from the clot, were examined 7 days after SAH, in which an autologous blood clot was bilaterally placed around major cerebral arteries.3. Compared with the sham-operated group, contractions in the clot removal groups at 48 and 72 h after SAH were reduced in MCP and enhanced in BAP.4. These results suggest that divergent vascular contractility may occur according to the distance between artery and clot if the clot is removed later than 48 h after SAH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1440-1681.1999.03063.x
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  • 9
    Electronic Resource
    Electronic Resource
    INOTROPIC RESPONSES OF ISOLATED ATRIAL AND VENTRICULAR MUSCLE FROM THE DOG HEART TO INOSINE, GUANOSINE AND ADENOSINE (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Clinical and experimental pharmacology and physiology 8 (1981), S. 0 
    Details
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The inotropic effects of inosine, adenosine and guanosine were compared in isolated and blood-perfused canine atrial and ventricular muscle preparations paced at 1.5 2.5 Hz.2. In isolated atria, guanosine and inosine usually had positive inotropic effects, but adenosine consistently had a marked negative inotropic effect.3. In ventricular muscles, the three purine compounds examined produced dose-related positive inotropic responses, but adenosine also produced a slight negative inotropic response which preceded the positive inotropic response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1681.1981.tb00148.x
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  • 10
    Electronic Resource
    Electronic Resource
    POTENTIATION OF THE NEGATIVE CHRONOTROPIC AND INOTROPIC EFFECTS OF ADENOSINE BY 2-PHENYLAMINOADENOSINE (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Clinical and experimental pharmacology and physiology 10 (1983), S. 0 
    Details
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Effects of 2-phenylaminoadenosine on SA nodal pacemaker activity and atrial contractility were studied, using eleven isolated, blood-perfused dog atrial preparations. The compounds were administered via the cannulated sinus node artery of the isolated atrium.2-Phenylaminoadenosine induced negative chronotropic and inotropic effects and was 100 times less potent than adenosine in this action.The interaction between adenosine and 2-phenylaminoadenosine was studied. 2-Phenylaminoadenosine potentiated the effect of adenosine on atrial muscle, but not that of acetylcholine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1681.1983.tb00164.x
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