[Parasympathetic regulation of the heart in teleosts and factors determining the regulatory direction of the chronotropic effect].

Changes in the sinus rhythm of the cod heart in response to single brief bursts of stimuli (50-200 msec) delivered to the vagus with different intervals after P-wave, were investigated. The moment of vagal stimulation in respect to cardiac cycle, the duration of free running cardiac period and intensity of nerve activity were found to be the factors determining the regulatory direction of chronotropic effects (acceleration or inhibition of the heart). Possible mechanisms of parasympathetic acceleration of the cardiac rhythm are discussed.