THE MODE OF ACTION OF CERTAIN DRUGS WHICH STIMULATE RESPIRATION

¹ Department of Physiology, Middlesex Hospital Medical School, London

1. The mode of action of a number of respiratory stimulants—namely nicotine, lobeline, potassium, cyanide, sparteine, ethyl aceto-acetate, acetyl-acetone and sodium salicylate—has been examined in the cat under chloralose anaesthesia and in the decerebrate preparation to determine the nature and relative importance of the action of these substances on the respiratory centre (direct action) and on the sino-aortic nerve endings (peripheral action) respectively.

2. Nicotine and lobeline in small and moderate doses stimulate respiration almost exclusively by a peripheral action (confirmatory of Heymans and co-workers). Large doses may also directly stimulate the respiratory centre.

3. The initial stimulating action of cyanide and the entire stimulating action of sparteine is reflex in origin (confirmatory of Heymans and co-workers and Zunz and Tremonti). The direct initial action of these drugs is to depress the respiratory centre. In the decerebrate preparation cyanide produces a secondary prolonged stimulation which is independent of the integrity of the sino-aortic nerves.

4. The enol-containing group of drugs (ethyl aceto-acetate, acetyl-acetone and sodium salicylate) act both peripherally and centrally. The reflex effects predominate in the anaesthetized animal and the central in the decerebrate preparation.

5. The sensitivity of the respiratory centre to the direct excitatory action of certain drugs seems to be considerably greater than has been recognised by recent workers.