Acetylcholine release from airway cholinergic nerves in horses with heaves, an airway obstructive disease.

This research studied the release of acetylcholine from airway cholinergic nerves in horses with heaves, an airway obstructive disease, and its regulation by various receptors. The study found no significant difference in acetylcholine release from cholinergic nerves between normal horses and those affected by heaves, but identified that prejunctional alpha 2-adrenoceptors in affected horses are dysfunctional.

Experiment Methods

• The research was conducted on both normal horses and those suffering from heaves, an obstructive airway disease.
• Sections from trachealis strips and bronchial segments of these horses were put into 2-ml tissue baths.
• Acetylcholine release was stimulated using electrical field stimulation and measured with high-performance liquid chromatography (HPLC) having electrochemical detection.

Observations with Respect to Acetylcholine Release

• The rate of stimulated acetylcholine release from cholinergic nerves in the trachea was found to be no different between normal horses and those suffering from the obstructive airway disease.
• The muscarinic receptor antagonist atropine increased acetylcholine release to similar extents in the two groups of horses, indicating no dysfunction of muscarinic autoreceptors in the large airways of horses with heaves.

Prejunctional Alpha 2-Adrenoceptors’ Dysfunction

• An abnormality was observed in terms of the regulation of acetylcholine release through alpha 2-adrenoceptors. Clonidine, an alpha 2-adrenoceptor agonist, had lesser inhibitory influence over acetylcholine release from the bronchi in horses with heaves when compared to normal horses. This suggests a dysfunction of prejunctional alpha 2-adrenoceptors in such horses.

No Influence of Prostaglandin E2 or Indomethacin

• Prostaglandin E2 (PGE2) or the cyclooxygenase inhibitor indomethacin, when added exogenously, showed no effect over acetylcholine release, thereby suggesting that decreased airway mucosal PGE2 production in horses with heaves, as previously reported, does not affect the release of acetylcholine.