The effects of propranolol on acute hypertension of anesthetized dogs and on the carotid sinus reflex responses of anesthetized and awake dogs.

Experiments are presented to show the effects of (1) propranolol on tbe response of systolic blood pressure and diastolic blood pressure to bilateral carotid artery occlusion in choralose-anesthetized dogs; (2) the effects of propranolol on acute hypertensive states in chloralose-anesthetized dogs; and (3) the effects of propranolol on the response of trained awake dogs to bilateral carotid artery occlusion. Acutely, propranolol in successive doses administered intravenously lowered the systolic and diastolic blood pressure response to 35% and 27%, respectively, of the original response during bilateral carotid artery occlusion. There was no significant change in the systolic and diastolic blood pressure of controls. Systolic blood pressure, diastolic blood pressure, ventricular contractile force, dp/ dt, and heart rate, which were elevated by double vagotomy and carotid sinus denervation, were returned to control levels by doses of propranolol. Hypertensive blood pressures of dogs infused with angiotensin and norepinephrine were made normotensive by simultaneous infusion or bolus injection of propranolol. Administered centrally in "isolated head" experiments (dogs) and ventromedial nucleus (in cats), propranolol had no effect on acute hypertension or on carotid sinus reflex response or ventromedial nucleus stimulation. The systolic and diastolic blood pressure responses to bilateral carotid artery occlusion in awake dogs were not significantly altered after the 1st week of daily treatment with propranolol (2.5 mg/kg). The responses of both the systolic and diastolic blood pressure to bilateral carotid artery occlusion decreased, however, after 1 week of daily propranolol administration at 5.0 mg/kg and there was a further decrease in heart rate, and in systolic and diastolic blood pressure responses to bilateral carotid artery occlusion when propranolol was raised to 7.5 mg/kg in daily doses for 1 week.