Pharmacological evidence for two types of baroreceptors in the carotid sinus of the cat

Abstract

The effects of general anaesthetics and of phentolamine on the vasomotor reactions, evoked from the carotid sinus region, were studied in the prethalamic cat. 1. 1. The carotid occlusion reflex (COR) could regularly be evoked after destruction of the chemoreceptors in the glomus, 3ut the rise of blood pressure was smaller than that produced by the COR in cats with intact chemoreceptors. The response disappeared after division of the sinus nerve. 2. 2. Subnarcotic amounts of pentobarbitone (about 8 mg/kg) blocked the COR in both conditions while the hypotensive responses to carotid stretching or sinus nerve stimulation were abolished only by doses 2–3 times higher. 3. 3. In the cat with intact chemoreceptors, small doses of phentolamine eliminated the depressor responses, while much larger doses were needed to reduce the COR. 4. 4. Conversely, in the animal deprived of its glomus chemoreceptors, the residaul COR was more sensitive to phentolamine than were the depressor responses. 5. 5. It is concluded that there are two types of baroreceptors present in the wall of the carotid sinus which react to a rise or a fall respectively of the pressure in the sinus.