Atropine prevents the reflex tracheal relaxation arising from the stimulation of intestinal and skeletal muscle afferents in dogs

Using cholinergic and beta-adrenergic antagonists, we characterized the efferent arms of two reflex arcs that relax tracheal smooth muscle in dogs. The reflex arcs investigated were activated by the capsaicin-induced stimulation of afferent endings in the intestine and in the hindlimb. We found that the reflex tracheal relaxations were due to a withdrawal of a tonic cholinergic input. Beta-adrenergic pathways played little role in causing these reflex responses.