Summary
Mice were anaesthetized by a maximal narcotic but not lethal dose of ethyl urethane. Continuous electronic computing of their ECG's shows marked sinus bradycardia from 30 min to 7 h after injection. After 7 h bradycardia is reduced more and more, but the initial frequency is not yet reestablished 12 h after injection. There occur arrhythmias in a similar time course.
Heart rhythm shows a very marked periodic shift: Pronounced bradycardia with increased arrhythmia is followed by faster and more regular heart beats. This shifting is produced regularly by nearly all the mice for several hours. Its main period is 7.6 min and its main frequency alteration is 0.83 c.p.s.
The PR interval remains nearly unaffected.
All frequency effects are mainly brought about by changing correspondingly the TP-intervals of the ECG. Thus the origin of the frequency alterations is to be found within the CNS or its autonomic pathways to the sinus node, within the sinus node itself, or in the sinauricular conduction system.
Urethane is not suitable for immobilizing mice in order to measure their heart function because of its strong effects on heart rhythm.
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Heimatanschrift: Prof. Dr. P. E. Haeser, SJ, Univers. do Vale do Rio dos Sinos, S. Leopoldo, R. S. Brasil.
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Lehr, E., Haeser, P.E. & Werner, G. Die chronotrope Wirkung der Urethan-Narkose auf das Mäuseherz. Naunyn-Schmiedeberg's Arch. Pharmacol. 273, 386–393 (1972). https://doi.org/10.1007/BF00499672
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DOI: https://doi.org/10.1007/BF00499672