Autoradiographic localization of substance P binding sites in guinea-pig airways

The distribution of substance P (SP) binding sites in guinea-pig airway was examined by in vitro autoradiography with tritium- and iodine-labeled SP. Specific SP binding sites were most abundant in tracheobronchial smooth muscle but were also detected in the mucosa/submucosa. Binding within the mucosa/submucosa was especially high in the region of glands. Binding of iodine-labeled SP to cartilage was negligible. Tritium-labeled SP bound non-specifically to airway cartilage. These observations are consistent with the proposed effects of SP-containing afferent nerves on airway resistance and vascular permeability. The localization of specific SP binding sites suggests that SP may also affect exocrine glands in the respiratory tract.