The lung in relation to vasoactive polypeptides.

Among the metabolic functions of the lungs are the formation, release, activation and inactivation of biologically active peptides. The following peptides may be present or formed in normal lung: vasoactive intestinal peptide or a peptide closely related to it, a spasmogenic peptide not yet fully identified, bradykinin, substance P, a bombesin-like peptide (especially in fetal and neonatal lung), and eosinophil-chemotactic peptides. These peptides are found in special neuroendocrine cells, in neurons, or in mast cells. Normal lung also inactivates bradykinin and activates angiotensin; both processes are catalysed by the same enzyme (kininase II or angiotensin-converting enzyme), located in pulmonary vascular endothelium. Pulmonary tumours and certain non-tumorous lesions can produce and release a variety of peptide hormones that are not normally generated by the lung in substantial amounts. This 'ectopic' secretion of hormones may be detectable only by sensitive assays or may result in specific clinical syndromes.