Visceral reflex responses following right intra-atrial injection of phenyldiguanide in rats.

1. Intra-atrial injection (right atrium) of pdg in nembutal anaesthetised rats produced bradycardia, hypotension and apnoea followed by hyperpnoea. In very lightly anaesthetised rats, injection of pdg close to the aortic valves produced similar responses and those responses disappeared on maintaining the animals in well-anaesthetised condition. 2. Administration of pdg either into the cerebral circulation or into cerebral ventricles did not produce bradycardia and apnoea. 3. The afferent pathway for these autonomic responses runs in vagus nerve, as shown by experiments before and after bilateral vagotomy. 4. The electrical activity of both expiratory and inspiratory muscles was inhibited during end-expiratory apnoea phase following injection of pdg into the right atrium. 5. Glycine, administered centrally or intravenously, exhibited blockade of pdg induced autonomic responses for more than forty minutes.