Modulation of the baroreceptor reflex by angiotensin II and other vasoactive drugs in anaesthetized greyhounds.

1. The effects of vascular infusions of acetylcholine, angiotensin II, noradrenaline and prostaglandin F2 alpha on the baroreceptor reflex were studied in the anaesthetized greyhound. 2. Vertebral artery infusions of low doses of angiotensin II, but not of acetylcholine or prostaglandin F2 alpha, resulted in a significant reduction in the depressor response to carotid sinus nerve stimulation. 3. The increases in blood pressure and heart rate in response to bilateral carotid artery occlusion were not significantly changes during vertebral artery infusions of acetylcholine, angiotensin II or prostaglandin F2 alpha. 4. The increases in blood pressure in response to intravenous infusions of noradrenaline were significantly enhanced during vertebral artery infusions of acetylcholine and angiotensin II, but not of prostaglandin F2 alpha. The bradycardia during noradrenaline infusions was significantly enhanced by angiotensin II alone. 5. The depressor response to carotid sinus nerve stimulation was significantly reduced during intravenous infusions of both noradrenaline and angiotensin II. 6. It is considered that although angiotensin II can be shown to have a specific central action to attenuate the response to carotid sinus nerve stimulation, the role of this action in the complete baroreceptor reflex is unproven.