Effect of Acute Sympathectomy on Responses to Angiotensin and Norepinephrine

The vasopressor response to angiotensin administered intra-arterially to the perfused hindquarters of the dog was reduced significantly after acute sympathectomy. Responses to norepinephrine and tyramine remained unchanged. Similar results were obtained following gangliouic blockade with hexamethonium and cervical spinal transection. After the response to augiotensin was reduced following sympathectomy, the cut lumbar sympathetic nerves were stimulated electrically. During the period of stimulation, an increase in the vasoconstrictor effect to angiotensin was obtained, but complete restoration to the control magnitude was not seen consistently. Possible mechanisms for the reduction in the response to angiotensin following sympathectomy are discussed. The present evidence suggests that the tonic discharge of normally functioning sympathetic nerves is capable of facilitating the response to angiotensin and that sympathectomy results in an abolition of this effect.