Journal of Applied Physiology, Vol 69, Issue 5 1594-1598, Copyright © 1990 by American Physiological Society
Nonadrenergic inhibitory nerves attenuate neurally mediated contraction in cat bronchi
T. Aikawa, K. Sekizawa, S. Itabashi, H. Sasaki and T. Takishima
First Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
Effects of nonadrenergic and noncholinergic (NANC) inhibitory nerves on
cholinergic neurotransmission were examined in isolated bronchial segments
from cats in the presence of propranolol (10(-6) M) and indomethacin
(10(-6) M) by use of electrical field stimulation (EFS) techniques. EFS
caused contraction alone in tissues at the baseline tension and biphasic
responses (contraction and relaxation) in tissues precontracted with
5-hydroxytryptamine. Contraction was abolished by atropine (10(-6) M), and
relaxation was abolished by tetrodotoxin (10(-6) M). At the baseline
tension, EFS at frequencies greater than 10 Hz inhibited the subsequent (4
min later) contraction induced by EFS at 1-5 Hz. EFS-induced inhibition was
stimulus frequency dependent and reached maximum at 20 Hz. However, EFS at
20 Hz did not inhibit the subsequent contractile response to acetylcholine
(10(-7) to 10(-3) M). Exogenously applied vasoactive intestinal peptide
mimicked EFS-induced inhibitory effects, but substance P and calcitonin
gene-related peptide did not. The inhibitory effect of EFS at 20 Hz was not
altered by pyrilamine, cimetidine, naloxone, methysergide, phentolamine,
BW755C, AF-DX 116, or removal of epithelium. These results imply that the
NANC transmitter acts via presynaptic cholinergic receptors.
