A quantitative study of the effects of cholinergic drugs on carotid chemoreceptors in the cat.

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Abstract
Conflicting qualitative evidence exists concerning the effects on chemoreceptor activity of some drugs which influence the cholinergic system. Quantitative evidence was obtained which should resolve the conflict. Experiments were performed in pentobarbitone-anesthetized cats in which the activity of chemoreceptor units in the sinus nerve was used to assess chemoreceptor responses. The effects of drugs on responses to intra-arterial ACh [acetylcholine] and NaCN were determined from dose-response data obtained from several animals and expressed as mean dose ratios. The chemoreceptor response to ACh was slightly inhibited by atropine, .alpha.- and .beta.-bungarotoxin and HC-3 [hemicholinium-3] almost completely suppressed by mecamylamine and markedly potentiated by physostigmine. Concomitant responses to NaCN were unaffected by atropine, .beta.-bungarotoxin, mecamylamine or physostigmine. There was a slight inhibition following .alpha.-bungarotoxin and a potentiation after HC-3. The results do not support the theory that ACh is an excitatory sensory transmitter in the carotid body.