Distribution of Vasoactive Intestinal Polypeptide-Immunoreactive Structures in the Opossum Esophagus

Abstract

Physiologic evidence that vasoactive intestinal polypeptide (VIP) regulates esophageal smooth muscle in the opossum has been gathered without knowledge of the distribution of VIP in that organ. We examined planar sections stained for VIP by the avidin-biotin complex method, measured VIP content in mucosa and muscularis propria by radioimmunoassay, and compared neural structures reactive to VIP antiserum with those revealed by osmication in the presence of zinc iodide. Immunoreactive terminal nerves interlaced smooth muscle bundles in all layers in all smooth muscle regions, formed loose tangled knots about widely dispersed muscle cells in striated muscle, and supplied vessels and submucosal glands. Bipolar interstitial cells in the circular muscle layer stained by osmication were not VIP-immunoreactive. Perikarya in both submucous and myenteric plexuses were VIP-immunoreactive. Vasoactive intestinal polypeptide-immunoreactive oval cells with round unstained nuclei and a faintly granular cytoplasm were scattered in the muscle in all regions and were concentrated in the planes of the plexuses. Vasoactive intestinal polypeptide content of muscularis propria in the smooth muscle esophageal body exceeded (p less than or equal to 0.05) that in the striated muscle esophageal body and the sphincter region, but contents in the latter two regions did not differ (p greater than or equal to 0.05). Mucosal content exceeded that of muscularis propria. The broad distribution and diversity of immunoreactive structures suggest that VIP may have functions in this organ besides the regulation of smooth muscle.