Xy. Zhang et al., EXCITATORY PREJUNCTIONAL BETA(2)-ADRENOCEPTOR DISTRIBUTION WITHIN EQUINE AIRWAY CHOLINERGIC NERVES, Respiration physiology, 106(1), 1996, pp. 81-90
We examined the effect of activation of beta(2)-adrenoceptor (AR) by i
soproterenol (ISO) on acetylcholine (ACh) release evoked by electrical
field stimulation (EFS: 20 V, 0.5 Hz, 0.5 msec) from cholinergic nerv
es in five regions of equine airways. We also tested if the effect of
ISO was dependent on epithelium or prostanoids by examining the effect
of ISO on ACh release in the presence and absence of epithelium or cy
clooxygenase inhibition. Trachealis strips or bronchial rings were pre
incubated for 60 min with 10(-7) M atropine, 10(-6) M neostigmine, and
10(-5) M guanethidine. The ACh amount was measured by high-performanc
e liquid chromatography with electrochemical detection. Isoproterenol
(10(-8)-10(-6) M) augmented ACh release throughout the whole ah-way in
a concentration-dependent manner. Rubbing off the epithelium potentia
ted EFS-induced ACh release but neither epithelium removal nor cycloox
ygenase inhibition affected the magnitude of ISO-induced augmentation
of ACh release. These results indicate that in equine airway parasympa
thetic nerves: (1) excitatory prejunctional beta(2)-adrenoceptors are
distributed throughout the tracheobronchial tree; (2) the function of
this excitatory beta(2)-adrenoceptor is independent of endogenous pros
tanoids and epithelium; and (3) there is an epithelium-derived factor
that inhibits ACh release.