MECHANISMS OF CAROTID BODY STIMULATION

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Abstract
Evidence that both an intracellular change in pH and a cholinergic mechanism are involved in the initiation of carotid body reflexes is cited, and the question of the origin and site of action of the cholinergic substance is discussed in terms of the known morphology of chemo-receptor tissue. This analysis indicates that the chemorecep-tor cells are the source of the humoral agent, and that its action is at the point of contact between chemoreceptor cells and sensory nerve endings. While the carotid body of the cat is too small to allow direct detn. of its acetyl-choline content, the presence of true cholinesterase is closely correlated with the presence of acetylcholine. Therefore, carotid bodies from 12 cats were analyzed for the cholinesterases by a microchemical titrimetric method. The true cholinesterase coefficient of the carotid body was 0.48 as compared with a true cholinesterase coefficient of 2.5 in the adrenal medulla, and 9.6 in the superior cervical ganglion. While the authors believe the cumulative evidence for the action of a humoral agent in carotid body physiology is valid, the low true cholinesterase values obtained in the present expts. indicate that acetylcholine is probably not the mediator involved.