Normal hearts exhibit a positive time difference between the end of ventricular contraction and the end of QT interval, which is referred to as the electromechanical (EM) window. Drug-induced prolongation of repolarization may lead to the negative EM window, which was proposed to be a novel proarrhythmic marker. This study examined whether abnormal changes… (More)
Following a burst of pulses applied to the vagus nerve with progressively incremental delay after the P wave of the ECG, the narrow zone of the cardiac cycle was identified where even a small shift of the vagal burst position evoked an abrupt alteration of the chronotropic effect magnitude. Met-enkephalin potentiated the phase-dependent vagal chronotropic… (More)
In experiments on anesthetised cats we investigated functional significance of different cholinergic mechanisms regulating the magnitude of vagal chronotropic effect components, inhibitory tonic and synchronizing. It was established that inhibitory tonic vagal component is determined by intensity of acetylcholine hydrolysis and total amount of excited… (More)
In anaesthetised cats, effects of 24 regulatory peptides upon inhibitory tonic and synchronizing components of vagal chronotropic action, were studied. The findings allowed to divide the peptidergic vagotropic activity into three types: (1) a selective action upon inhibitory tonic vagal effect; (2) a selective modulation of synchronizing vagal effect; (3)… (More)
Administration of met-enkephalin to anesthetized cats promoted inhibition of the heart rate, weakening of the vagus chronotropic effect with changes of its functional structure consisting of suppression of the inhibitory tonic effect and potentiating synchronizing component. The comparison of the peptide's vagotropic action in the initial conditions versus… (More)
In cats, magnesium, potassium and finoptin diminished the vagal chronotropic effect whereas calcium potentiated it. In potassium chloride administration, the vagotropic action was due to a selective diminishing of the tonic component.
Effects of met-enkephalin and enkephalin analogue Tyr-D-Orn-Gly-Phe involved a depressing vagotropic action due to a selective decrease in the tonic component. The data obtained suggests different actions of met-enkephalin and its analogue upon the synchronizing component of vagal chronotropic action.
The effect of met- and leu-enkephalins in cats was characterised by depressing vagotropic action due to a selective decrease in the tonic component. The potentiation of synchronizing actions may serve as an index of a reliable and stable mechanism of the beat-by-beat control of the cardiac rhythm.