AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 1 140-G146, Copyright © 1986 by American Physiological Society
Characterization of substance P effects on canine antral muscle
E. A. Mayer, G. van Deventer, J. Elashoff, S. Khawaja and J. H. Walsh
Synthetic substance P increased the frequency and amplitude of
spontaneously occurring contractions of circular and longitudinal muscle
strips from canine gastric antrum in vitro. In longitudinal muscle, ED50
values calculated for frequency and amplitude were 3.7 X 10(-9) M and 9.7 X
10(-7) M, respectively. The effect of substance P on frequency in both
layers and on amplitude in the circular layer was myogenic and unrelated to
receptors for acetylcholine, norepinephrine, serotonin, histamine, and
enkephalins. In the longitudinal muscle the amplitude response was
partially inhibited by tetrodotoxin, atropine, and hexamethonium. The
effect on amplitude but not on frequency was dependent on extracellular
calcium. When compared to other stimulants of antral muscle contraction,
the biological potency of substance P was higher than that of acetylcholine
but significantly lower than that of gastrin and bombesin. Two putative
substance P antagonists ([D-Pro2,D-Phe7,D-Trp9]substance P and [D-Pro2,
D-Trp7,9]substance P) did not block the response of longitudinal muscle to
substance P. Only the chronotropic response to substance P showed
consistent, prolonged desensitization. These findings suggest that the
mechanisms mediating the response to substance P in the canine antrum are
different from other reported tissues.
