ACTION OF PROSTIGMINE AND ACETYLCHOLINE ON RESPIRATION

¹ Department of Physiology, Middlesex Hospital Medical School, London, W. 1.

1. The effects of intravenously injected prostigmine and acetylcholine on the respiration of cats under chloralose anæsthesia and of decerebrate cats were examined.

2. Prostigmine inhibits respiration of cats under chloralose anæsthesia; the depression of breathing may be either preceded or followed by periods of respiratory stimulation. The inhibitory effect of prostigmine is partially annulled by atropine, and enhanced by section of the vagi and denervation of the carotid sinus nerves.

3. The stimulatory phenomena preceding or subsequent to the inhibition are more marked in decerebrate preparations. The initial stimulation is usually abolished by elimination of the vaso-sensory nerves.

4. The inhibition of breathing and the secondary stimulation are partly due to an action on the respiratory and spinal centres.

5. Eserine inhibits respiration; it is less potent in this respect than prostigmine.

6. Acetylcholine produces a "triple response" consisting of initial stimulation, subsequent inhibition, and secondary stimulation. Injection of an anticholinesterase may result in (1) a simple potentiation of the effects of previously injected acetylcholine, (2) a marked enhancement of the inhibitory phase of the acetylcholine action, (3) a marked potentiation of the initial stimulation; this last effect disappears after the elimination of the vaso-sensory nerves.

7. After elimination of the vaso-sensory nerves, acetylcholine mainly inhibits respiration; secondary stimulation was sometimes observed.

8. Analysis of the results shows that acetylcholine stimulates the chemo-receptor zones in the carotid sinus and the aortic arch. The inhibitory effects on breathing are partially due to an action of acetylcholine on the respiratory centre and the spinal cord.