I.V. LIGNOCAINE IN REFLEX AND ALLERGIC BRONCHOCONSTRICTION

The protection against bronchospasm afforded by infusions oflignocaine was tested in dogs anaesthetized with thiamylal bychallenge with aerosols of citric acid (CAA) or ascaris antigen(AAA). During the infusion of lignocaine, the response to CAAwas blocked or markedly attenuated, but AAA still elicited alarge increase in pulmonary resistance (R_L). In untreated dogs,CAA increased R_L from 0.14±0.05 (mean±SEM) kPalitre^–1 s to 1.09±0.18, whereas in dogs treatedwith lignocaine, R_L was 0.19±0.09 before challenge withCAA and 0.44±0.13 after challenge. AAA increased R_L.from 0.14±0.06 kPa litre¹ s to 3.01±0.65 in untreateddogs, and from 0.34±0.10 kPa litre^–1 to 1.85±0.69in dogs treated with lignocaine. Blood concentrations of lignocainewere 1.5±0.3 and 2.5±0.6µg ml^–1 duringchallenge with CAA and AAA, respectively. We conclude that lignocaine,at blood concentrations which will reduce the risk of cardiacarrhythmia, markedly reduces reflex bronchoconstriction, buthas relatively little effect on that initiated by allergic mediators.