The non-adrenergic, vagal efferent system to the lung: does it exist, or is an artefact?

A third efferent pathway to the lungs - the non-adrenergic vagal inhibitory system - has previously been invoked to explain the residual neurally-mediated bronchodilatation, that is obtained after the administration of cholinergic and adrenergic blocking drugs. However, the experimental results cited as evidence for the existence of this third efferent pathway, can also be explained by an alternative mechanism, involving local axon reflexes in afferent fibres from lung receptors. If this latter explanation is correct, then the existence of the third efferent pathway is an artefact resulting from the experimental conditions. Caution should therefore be exercised before looking for ways of controlling this system, until it has been proven exactly which is the mechanism mediating it.