Release of autonomic neuromediators by local ventricular electrical stimulation

stimuli were applied to the ventricular epicardium in pentobar-bital-anesthetized dogs. The trains, delivered during the abso-lute refractory period via Walton-Brodie strain gauge arches, resulted in a highly localized potentiation of ventricular con-tractile 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 P-adrenergic blockade with tolamolol, indicating that the response was probably me-diated 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 augmenta