Circulatory Control via Vagal Afferents

Abstract Castenfors, J. and T. Sjöstrand. Cirulatory control via vagal afferents. I. Adjustment of heart rate to variations of blood volume in the rat. Acta physiol. scand. 1972. 84. 347–354. On withdrawal of 20–35 % of the blood volume the heart rate may increase, decrease or remain unchanged. The effect has been found to be dependent on animal strain, anesthesia and the autonomic balance. In Sprague‐Daley rats a lowering of the heart rate has been practically constantly observed, sometimes after an initial rise. Bilateral vagotomy eliminates the reduction of heart rate but does not obviously influence the rise. Atropine inhibits the bradycardia largely, and propranolol the tachycardia. On administration of both atropine and propranolol, both the lowering and the rise of heart rate are entirely eliminated. Ligation of the common, external and internal carotid arteries eliminates the bradycardia. Bilateral exclusion of afferents via the communicating branch between the superior and inferior laryngeal nerves usually eliminates the bradycardia. It is presumed that in the rat the heart rate response to hemorrhage is determined by antagonistically acting receptor mechanisms which affect the autonomic tone on the heart, one in a vagotonic and the other in a sympathicotonic direction. The afferents mediating the bradycardia run entirely or for the most part via the recurrent nerve and the laryngeal com‐municans to the cranial part of the cervical vagus.