I.V. lignocaine in reflex and allergic bronchoconstriction.

The protection against bronchospasm afforded by infusions of lignocaine was tested in dogs anaesthetized with thiamylal by challenge with aerosols of citric acid (CAA) or ascaris antigen (AAA). During the infusion of lignocaine, the response to CAA was blocked or markedly attenuated, but AAA still elicited a large increase in pulmonary resistance (RL). In untreated dogs, CAA increased RL from 0.14 +/- 0.05 (mean +/- SEM) kPa litre-1 s to 1.09 +/- 0.18, whereas in dogs treated with lignocaine, RL was 0.19 +/- 0.09 before challenge with CAA and 0.44 +/- 0.13 after challenge. AAA increased RL from 0.14 +/- 0.06 kPa litre-1 s to 3.01 +/- 0.65 in untreated dogs, and from 0.34 +/- 0.10 kPa litre-1 to 1.85 +/- 0.69 in dogs treated with lignocaine. Blood concentrations of lignocaine were 1.5 +/- 0.3 and 2.5 +/- 0.6 microgram ml-1 during challenge with CAA and AAA, respectively. We conclude that lignocaine, at blood concentrations which will reduce the risk of cardiac arrhythmia, markedly reduces reflex bronchonconstriction, but has relatively little effect on that initiated by allergic mediators.