Cardiovascular effects of thoracic afferent nerve stimulation in conscious dogs

Afferent stimulation of a severed thoracic autonomic nerve in 18 conscious dogs produced in 13 instances hypertension and in 5 instances hypotension. Reflex hypertension was usually accompanied by augmented atrial and ventricular force of contraction. The hypertension could be maintained for over 5-min duration by constant stimulation. Inotropic changes accompanying this hypertension were accentuated following atropine administration and abolished by propranolol. Blood pressure changes following atropinization were initially augmented. On the other hand reflex hypotension was accompanied by bradycardia and decreased atrial contractility. These changes were essentially abolished by atropine. Afferent nerve stimulation with frequences as low as 1 Hz initiated reflex changes. Maximal responses were obtained by stimulation frequencies of 10-15 Hz. It is concluded that significant and relatively sustained cardiovascular reflexes can be generated by stimulation of cardiac afferent nerves in conscious dogs.