Autoradiographic Localization of Substance P Binding Sites in Guinea-Pig Respiratory Tract

Autoradiographic binding sites for [125I]-Bolton-Hunter labelled substance P (BHSP) were investigated in the guineapig respiratory tract. Dense binding was observed on the smooth muscle of primary bronchi, secondary bronchi and terminal bronchioles. In the trachea, specific binding sites for BHSP were seen densely clustered over the trachealis muscle. Specific binding of BHSP to guinea-pig lung membranes was displaced by SP > SK > NK, indicating binding to a P-type site. No binding of BHSP was observed to arterioles in the lung. The presence of BHSP binding sites on guinea-pig respiratory smooth muscle is in accordance with the bronchoconstrictor actions of SP.