[Chronotropic effects on the heart during the interaction of parasympathetic and sympathetic regulatory influences].

In the frog heart isolated sinus node with intact extracardiac sympathetic and parasympathetic pathways or intracardiac nerves, the intracellular pacemaker APs and extracellular nervous activity of the parasympathetic postganglionic intracardiac pathways were recorded. Two major sympathetic-parasympathetic interaction patterns were revealed: the antagonistic and the augmentative ones. In initial deep bradycardia, sympathetic stimulation diminished the parasympathetic inhibition, whereas in initial parasympathetic tachycardia, sympathetic stimulation augmented these parasympathetic effects. The recording of the intracellular pacemaker AP showed the effect of a complicated interaction between the sympathetic and parasympathetic transmitters on the heart pacemaker. Parasympathetic postganglionic nervous activity changed in two ways: there was either an attenuation during intense sympathetic stimulation or an augmentation during a weak sympathetic stimulation. Relative significance of the sympathetic and parasympathetic systems in the heart rate control and possible mechanisms of the two patterns of sympathetic-parasympathetic interactions, are discussed.