AJP - Lung Cellular and Molecular Physiology, Vol 268, Issue 3 368-L373, Copyright © 1995 by American Physiological Society
Catecholamine affects acetylcholine release in trachea: alpha 2-mediated inhibition and beta 2-mediated augmentation
X. Y. Zhang, N. E. Robinson, Z. W. Wang and M. C. Lu
Department of Large Animal Clinical Sciences, Michigan State University, East Lansing 48824.
We investigated the effects of catecholamines on acetylcholine (ACh)
release from equine airway parasympathetic nerves. Trachealis strips were
suspended in 2-ml tissue baths with Krebs-Henseleit solution containing
atropine (10(-7) M), neostigmine (10(-6) M), and guanethidine (10(-5) M).
Electrical field stimulation (20 V, 0.5 ms, 0.5 Hz, for 15 min) was
applied, and ACh was measured by high-performance liquid chromatography
with electrochemical detection. Epinephrine (Epi) and norepinephrine (NE)
inhibited ACh release in a concentration-dependent manner. Inhibition was
attenuated by the alpha 2-adrenoceptor antagonist idazoxan (10(-6) M) but
not by the alpha 1-antagonist prazosin (10(-6) M). After alpha 2-blockade
with idazoxan (10(-5) to 10(-4) M), Epi but not NE augmented ACh release.
Isoproterenol (10(-7) to 10(-5) M) increased ACh release, an effect that
was reversed by the beta 2-adrenoceptor antagonist ICI-118,551 (10(-5) M)
but not by the beta 1-adrenoceptor antagonist atenolol (10(-5) M). Our
results indicate that horse airway cholinergic nerves are modulated by both
alpha 2-inhibitory and beta 2-excitatory adrenoceptors, with the former
being predominant.
