AJP - Gastrointestinal and Liver Physiology, Vol 248, Issue 6 655-G662, Copyright © 1985 by American Physiological Society
Capsaicin effects on muscularis mucosa of opossum esophagus: substance P release from afferent nerves?
H. Robotham, J. Jury and E. E. Daniel
The effects of capsaicin on the function and structure of muscularis mucosa
of opossum esophagus were studied. In this tissue there are numerous nerves
containing a substance P-like immunoreactive substance (SPLS), and
electrical field stimulation (EFS) leads to a phasic response that appears
to be due to release of acetylcholine, followed by a tonic response at
higher frequencies of stimulation that appears to be due to release of a
SPLS. The acetylcholine released by EFS and exogenous muscarinic agonists
inhibits release of this SPLS (8). In the present study capsaicin (5 X
10(-5) M) was shown to cause a tonic submaximal contraction in most cases.
This was prevented by substance P tachyphylaxis and by pretreatment with
the partial agonist [D-Pro2, D-Trp7,9]substance P, the antagonist [D-Arg1,
D-Trp7, Leu11]substance P, and tetrodotoxin. This response to capsaicin
could not be repeated even after 2 h. Capsaicin also abolished the tonic
response to high-frequency EFS without affecting phasic responses and
reduced markedly the enhanced tonic response after atropine had abolished
the phasic response. This occurred with or without a preliminary
contraction to capsaicin. This tonic response to high-frequency EFS
recovered completely 1-2 h after washing out capsaicin. Then, a further
administration of capsaicin had no direct effect but again abolished tonic
responses to EFS. Capsaicin reduced responses to exogenous substance P or
carbachol only partially. When tissues were fixed and studied after
capsaicin had abolished tonic responses to EFS, specific damage to nerve
varicosities or synaptic vesicles in nerve varicosities could not be
demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)
