Prejunctional alpha 2-adrenoceptors inhibit acetylcholine release from cholinergic nerves in equine airways.

This study investigates the role of alpha 2-adrenoceptors in inhibiting the release of acetylcholine, a neurotransmitter, from nerves that control the contraction of smooth muscle in horse airways.

Overview

• The study’s primary aim is to identify the existence and function of alpha 2-adrenoceptors on specific nerve cells, known as cholinergic nerves, in horse airway smooth muscle. These receptors when activated, inhibit the transmission of signals by these nerves that control muscle contraction.

Methodology

• The researchers stimulated these muscle contractions by using an electrical field stimulation (EFS) or by introducing a neurotransmitter, acetylcholine (ACh).
• Release of ACh was also induced by EFS, and its levels were measured using high-pressure liquid chromatography and electrochemical detection.
• If the ACh release and the muscle contraction response to EFS were inhibited by the alpha 2-adrenoceptor agonists, it suggested that these receptors are present on the cholinergic nerves.

Findings

• The alpha 2-adrenoceptor agonists, clonidine, and UK-14,304 affected the ACh release and muscle contraction response in a concentration-dependent manner. However, they did not influence the response to externally introduced ACh.
• This inhibition effect was lessened by alpha 2-adrenoceptor antagonists, yohimbine and idazoxan, but not by alpha 1-adrenoceptor antagonist prazosin. This confirms the presence and function of alpha 2-adrenoceptors on cholinergic nerves in the horse airway muscles.
• It is noteworthy that yohimbine did not have a significant effect under the given experimental conditions, suggesting that norepinephrine, a neurotransmitter, had no influence on these nerves via prejunctional alpha 2-adrenoceptors.