Cardiac sympathetic adrenergic pathways in which synaptic transmission is blocked by atropine sulfate.

1. Stimulation of the thoracic sympathetic nerve trunk caused a rise in arterial blood pressure and heart rate which was reduced but not abolished during the infusion of hexamethonium chloride, pentolinium tartrate, mecamylamine or tetraethylammonium chloride.2. Preganglionic stimulation no longer elicited a synchronous sC elevation in the post-ganglionic nerves. The persistent blood pressure and heart rate response was associated with an asynchronous discharge in these nerves.3. Both the persistent response and the asynchronous discharge were abolished by the intravenous injection of atropine sulphate in doses of 30 mug/kg.4. Atropine had no effect on spike amplitude or shape, conduction velocity or frequency response in either the pre- or post-ganglionic nerve trunks. Nor did it affect the rise in blood pressure and heart rate evoked by stimulation of the post-ganglionic cardiac sympathetic nerves.5. It is concluded that atropine partially blocked synaptic transmission in cardiac sympathetic adrenergic pathways.