Regulatory Peptides in the Mammalian Respiratory Tract*

The quantitative distribution of five biologically active peptides was determined by RIA and immunocytochemistry in various regions of cat, rat, and guinea pig respiratory tracts. Vasoactive intestinal polypeptide (VIP) and substance P were found in higher concentrations than cholecystokinin (CCK), SRIF, and bombesin. In general, higher concentrations were found in the main airways than in lung tissue. Immunocytochemistry localized VIP and substance P to autonomic nerves, whereas bombesin was found in very scattered mucosal endocrine cells of the cat bronchial epithelium. CCK and SRIF could not be convincingly localized by immunocytochemistry because of their low tissue concentrations. Species differences were noted, with high VIP but low substance P concentrations in the main airways of the cat; this relationship was reversed in the rat and guinea pig. Gel permeation chromatography of extracts revealed one peak, coeluting with the pure standard peptide, for CCK-8, SRIF, substance P, and VIP. Bombesin immunoreactivity was separable into two peaks, the major of which corresponded in position to that of gastrin-releasing peptide, and a later minor peak to the position of the bombesin standard. Thus, several potent peptides are present in the respiratory tract, which suggests the possibility that they play a significant role in controlling respiratory function.