Regulatory Peptides and Neuron-Specific Enolase in the Respiratory Tract of Man and Other Mammals

This short review deals with the distribution and cellular localization, in the respiratory tract, of five regulatory peptides (substance P, bombesin, vasoactive intestinal polypeptide (VIP), cholecystokinin, and somatostatin) and of a newly discovered neuroendocrine enzyme marker, neuron-specific enolase. Bombesin is found in typical mucosal endocrine cells, whereas the other regulatory peptides--principally substance P and VIP--are found, in significant concentrations, in autonomic nerves of the wall of the airways. Substance P, a putative sensory neurotransmitter, is found in autonomic nerves closely associated with the mucosal epithelium and the bronchial smooth muscle. VIP nerves, on the other hand, appear predominantly to innervate blood vessels, seromucous glands of the upper respiratory tract, and bronchial smooth muscle. The presence of neuron-specific enolase in both mucosal APUD cells and autonomic nerves has established this newly discovered neuronal enzyme as a useful marker for the entire neuroendocrine system of the lung and its derivative neoplasms.