Activity of lung irritant receptors in pulmonary microembolism, anaphylaxis and drug-induced bronchoconstrictions.

1. Lung irritant receptors have been studied in rabbits by recording action potentials from single vagal nerve fibres. Some of the rabbits were bilaterally vagotomized, and some paralysed and artificially ventilated.2. The receptors gave rapidly adapting irregular discharges on inflation and deflation of the lungs. Many were stimulated by insufflation of ammonia vapour into the lungs, and some by passage of a fine catheter into the right bronchial tree. The fibres had conduction velocities in the range 3.6-25.8 m/sec.3. The receptors were strongly stimulated by intravenous injections of histamine acid phosphate, 25-100 mug/kg. The response was considerably reduced by previous injection of isoprenaline which also reduced the bronchoconstriction due to histamine.4. The receptors were stimulated by intravenous injections of isoprenaline, phenyl diguanide and micro-emboli, and by anaphylaxis induced in rabbits previously sensitized to egg albumin.5. The receptor responses could not be closely correlated in size with simultaneous changes in total lung resistance, lung compliance, tidal volume or breathing frequency.6. It is concluded that, in rabbits with intact vagus nerves, lung irritant receptors contribute to the reflex hyperpnoea and bronchoconstriction of the conditions studied.