The Site of Cardiovascular Action of Angiotensin II in the Brain

The site of action of vertebral artery infusions of angiotensin was studied in the chloralose-anaesthetized greyhound. 2. The cardiovascular response to vertebral artery infusion of angiotensin (0·25–2·0 ng kg−1 min−1) was not reduced by clamping the basilar artery between the pons and the pyramidal decussation. There was no response to infusion of angiotensin through a catheter inserted in a rostral direction into the basilar artery above the clamp. The site of action must therefore lie caudal to the pons. 3. Transection of the spinal cord at the first cervical segment did not abolish the response to vertebral artery infusions, which was still mediated by the vagus nerve and abolished by subsequent vagotomy. The site of action must therefore lie rostral to the cervical cord. 4. Local infusions of angiotensin into the small arteries supplying the medulla produced a response similar to that obtained with vertebral artery infusion of angiotensin. 5. These results indicate that the site responsible for these central effects of angiotensin lies in the medulla.