[Dynamics of the vagus effect on the cardiac rhythm during blockade of various subtypes of M-cholinoreceptors in cats].
While single vagus bursts were used in cats with an incremental time delay following P-wave of the ECG, two zones were identified within the cardiac cycle differing from each other by their chronotropic responses. At the initial (approximately 120-130 ms) part of the cardiac cycle, an increase in the P-stimulus interval evoked a "moderate" (+8-16%) increment of the chronotropic response up to its maximal amplitude. Further increase of that interval provoked an "abrupt" (-80-90%) decrease of the vagus response. Block of M1-(pirenzepine), M2-(metoctramine and gallamine) or M3-(DAMP) cholinoreceptors diminished vagally-induced minimal and maximal prolongation of the ECG P-P interval and decreased the amplitude of its alterations associated with varying the position of vagus stimulus within the cardiac cycle. The coefficient delineating magnitude of the vagus effect over a zone with "moderate" changes of the chronotropic response was decreased after blocking the M1- and M2-cholinoreceptors, whereas duration of that zone was shortened following blockade of the M1- and M3-receptors. Velocity of the original vagus response and the rate of its subsequent decline decreased following blockade of the M1- and M2-subtypes of cholinoreceptors.
Osadchiĭ
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Kuban Medical Academy, 4 Sedin St., Krasnodar 350640, Russia.
D000818:Animals; D002415:Cats; D003864:Depression, Chemical; D004558:Electric Stimulation; D004562:Electrocardiography; D006321:Heart / Q000187:drug effects / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism; D009411:Nerve Endings / Q000502:physiology; D043643:Receptor, Muscarinic M1; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000378:metabolism*; D013268:Stimulation, Chemical; D014630:Vagus Nerve / Q000502:physiology*
D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D043643:Receptor, Muscarinic M1; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic
Dinamika vagusnogo vliianiia na ritm serdtsa koshki pri blokade otdel'nykh podtipov M-kholinoretseptorov.