Inhibitory effect of calcitonin gene-related peptide and calcitonin on opossum esophageal smooth muscle.

Calcitonin gene-related peptide (CGRP) is widely distributed in the gastrointestinal nerves, including those of the esophagus. The present investigation was undertaken to examine the effect and the mechanism of action of CGRP on the lower esophageal sphincter and esophageal contractions. This peptide caused dose-dependent relaxation of the lower esophageal sphincter. The D50 for inhibitory effect of intraarterial CGRP on the sphincter was 5.0 X 10(-13) mol/kg. Calcitonin gene-related peptide is 3000 times more potent than calcitonin. The effect of CGRP on the lower esophageal sphincter was partially antagonized by tetrodotoxin or black widow spider venom. The inhibitory effect of CGRP on the sphincter appears to be exerted at two levels: (a) at the sphincteric smooth muscle, and (b) at the noncholinergic, nonadrenergic inhibitory neurons. Calcitonin gene-related peptide also exerts a potent inhibitory effect on the peristaltic contraction of the esophageal body in response to swallowing and vagal efferent stimulation. Using immunohistochemical studies we also showed the presence of CGRP-immunoreactive neurons within the myenteric ganglia of the esophagus. These studies suggest that CGRP may play an important role as an inhibitory neurotransmitter in the esophagus.