Catecholamine affects acetylcholine release in trachea: alpha 2-mediated inhibition and beta 2-mediated augmentation.

The research paper discusses how catecholamines, specifically epinephrine and norepinephrine, influence the release of acetylcholine in the trachea of horses by acting on alpha 2 and beta 2 adrenoceptors.

Experimental Setup

• In this study, the researchers studied the effects of catecholamines on acetylcholine (ACh) release from the airway parasympathetic nerves of horses. To do this, they created a controlled environment using trachealis strips from the horses suspended in a Krebs-Henseleit solution (a specific type of salt solution used to maintain physiological conditions) containing atropine, neostigmine, and guanethidine.
• They then stimulated these work samples electrically and measured the amount of ACh released using high-performance liquid chromatography, a method used to separate and identify individual components in a sample.

Role of Epinephrine and Norepinephrine

• The research found that both epinephrine (Epi) and norepinephrine (NE) inhibited, or reduced, ACh release in a concentration-dependent manner. This implies that the higher the concentration of these catecholamines, the lower the ACh release.

Role of Alpha 2-Adrenoceptor and Beta 2-Adrenoceptor

• The inhibition effect was lessened by the alpha-2 adrenoceptor antagonist, idazoxan, but not affected by the alpha-1 antagonist prazosin. Antagonists are substances, which if present in the bloodstream, reduce the physiological action of another substance. Thus, by reducing the action of alpha-2 adrenoceptor, ACh release was increased, but there was no such effect for the alpha-1 adrenoceptor.
• The study further showed that epinephrine, but not norepinephrine increased ACh release after alpha-2 blockade. Alpha-2 blockade is a procedure where the action of the alpha-2 adrenoceptor is reduced or nullified.
• On the other hand, beta-2 adrenoceptor antagonist ICI-118,551, but not the beta-1 antagonist atenolol, reversed the augmentation of ACh release by isoproterenol, a drug that mostly stimulates beta-1 and beta-2 adrenoceptors.

Conclusion of the Study

• In conclusion, the study reveals that in the trachea or airway of horses, there is both alpha-2 inhibition and beta-2 excitation of ACh release from cholinergic nerves. However, the alpha-2 inhibitory action is predominant.