Cardiovascular responses to acetylcholine: Effects of pentobarbital and autonomic blocking agents

The effect of acetylcholine chloride (ACh) on heart rate (HR) and blood pressure (BP) was studied in four dogs, awake and under anesthesia by means of pentobarbital sodium. In the awake dog, ACh caused a triphasic change in HR—a rise, fall and secondary rise. The BP showed an initial gradual fall followed by a secondary precipitous fall coinciding with the fall in HR, and then return to base line. Anesthesia accentuated the precipitous fall in HR due to ACh, and narrowed the pulse pressure during the initial fall in BP due to ACh. The effects of atropine sulphate, propranolol and d-tubacurarine on the above were studied, indicating the roles of the sympathetic and parasympathetic systems in mediating the HR and BP reactions to ACh in the awake state and under pentobarbital sodium anesthesia.