Adenosine-Induced Cough: Mechanism
Adenosine causes cough by directly activating pulmonary C-fibers through adenosine A1 receptors located in the airways, triggering vagal sensory nerve pathways that initiate the cough reflex. 1
Neurophysiologic Mechanism
The cough response to adenosine occurs through a specific neural pathway:
Pulmonary C-fiber activation: Adenosine stimulates approximately 68% of pulmonary C-fibers when administered intravenously 1. These vagal sensory nerves terminate primarily in the larynx, trachea, carina, and large intrapulmonary bronchi 2.
A1 receptor-mediated: The stimulation is completely prevented by A1 adenosine receptor antagonists (like 1,3-dipropyl-8-cyclopentylxanthine), but not by A2 receptor antagonists 1. This confirms the mechanism is specifically A1 receptor-dependent.
Delayed onset: Unlike capsaicin which causes immediate C-fiber stimulation, adenosine has a latency of 6.5 seconds (range 3-18 seconds) and produces more prolonged activation 1. This explains why the urge to cough doesn't occur instantly but builds over several seconds after adenosine administration.
Clinical Context
The FDA label for adenosine confirms this mechanism is clinically relevant, listing bronchoconstriction and dyspnea as significant adverse effects 3. The label specifically warns that adenosine should be used with caution in patients with obstructive lung disease and is contraindicated in patients with bronchospasm or asthma 3.
Important Distinctions
Adenosine does NOT reliably trigger cough in anesthetized animals 4. Research in guinea pigs showed that adenosine selectively activates nodose ganglia C-fibers causing only tachypnea, not cough, in anesthetized states 4. This suggests the cough response requires intact higher brain processing and conscious perception of the urge to cough 2.
The bronchopulmonary C-fibers and mechanically sensitive, acid-sensitive myelinated sensory nerves play essential roles in regulating cough, with the brainstem and higher brain control systems processing this sensory information to generate the urge to cough 2.
Clinical Pitfall
Do not confuse the cough mechanism with bronchoconstriction: While both can occur with adenosine, they involve different pathways. Bronchoconstriction may involve mast cell activation and neural pathways 5, 6, whereas the direct cough stimulus is purely A1 receptor-mediated C-fiber activation 1.