[Adaptation of electropic and ionotropic vagal effects on the isolated rabbit atrium]

Long-time vagal stimulation induces a decrease of electrotropic and inotropic effects on the isolated rabbit atrium in spite of constant stimulation frequency. This decrease is defined as effect adaptation. To compensate this effect adaptation, the n. vagus was stimulated with increasing stimulation frequency. Compensation is possible for a certain period referred to as control time. The adaptation of the electrotropic effects is more delayed and weaker than the inotropic effect adaptation. The control times of the electrotropic effect are longer than those of the inotropic effect. Acetylcholine perfusion without vagal stimulation shows the same results. It was shown that the effect adaptaion does not result from depletion of acetylcholine stores or from co-stimulation of sympathetic nerve fibres. The effect adaptation is discussed as being the result of machano-electrical coupling.