[Relation between intracardiac reflex effects on the rate of atrioventricular conduction and parameters of neural...

Intracardiac nerves of the frog isolated heart were cut and the central or the peripheral end was stimulated. The atrioventricular (a-v) conduction was measured. The data showed that the intracardiac parasympathetic nervous system could induce both acceleration and deceleration of the a-v conduction, depending on the parameters of stimulation. Atropine blocked both the positive and the negative dromotropic effects whereas beta-adrenoblocking agent inderal was ineffective. The possible mechanism of the dromotropic effects observed are discussed.