Release of autonomic neuromediators by local ventricular electrical stimulation.

Trains of electrical stimuli were applied to the ventricular epicardium in pentobarbital-anesthetized dogs. The trains, delivered during the absolute refractory period via Walton-Brodie strain gauge arches, resulted in a highly localized potentiation of ventricular contractile force. The magnitude of the potentiation was directly related to the intensity of the trains. The positive inotropic response of either ventricle to trains of stimuli was abolished following chronic cardiac denervation or beta-adrenergic blockade with tolamolol, indicating that the response was probably mediated by the excitation of local sympathetic nerve fibers. Following the elimination of adrenergic influences, a slight negative inotropic response to trains of stimuli was observed in some animals. Administration of atropine blocked the negative inotropic response. When the adrenergic system was intact the administration of atropine resulted in a significant augmentation of the positive inotropic response of both ventricles to trains of stimuli. Thus in addition to norepinephrine release, it also appeared that electrical stimulation of the ventricles resulted in activation of local parasympathetic fibers with subsequent release of acetylcholine.