Bombesin-like immunoreactivity in the lung

THE first suggestion that the lung contained endocrine cells was made by Feyrter¹ when introducing the concept of a diffuse endocrine or paracrine system, composed of epithelial 'clear cells'. The presence of argyrophil cells in human and other mammalian lungs was later confirmed ^2,3 and it was shown that some of these cells contained amines, demonstrated by argent-affinity, formaldehyde-induced fluorescence (FIF), and the possession of neurosecretory type granules. They have variously been termed Feyrter cells⁴, Kultschitzky cells⁵, argy-rophil- fluorescent-granulated or AFG cells⁶, enteroch-romaffin-like cells⁷, neurosecretory cells⁸, pulmonary argyrophil cells⁹, endocrine or endocrine-like cells^10,11, and possess APUD cell characteristics^10-13. Endocrine cells are present within the bronchial and bronchiolar epithelium both as single elements and as groups of cells. Groups of innervated, endocrine-like cells termed neuroepithelial bodies have been demonstrated⁴. Some pulmonary endocrine cells contain 5-hydroxytryptamine^10,14 and possibly other amines, but no peptide product has yet been identified in them. Said ¹⁵ has proposed that the lung may produce a vasoactive peptide and it has subsequently been shown that the lung produces an angiotensin II-like peptide^16,17 and two vasoactive peptides¹⁸, although the cellular origin of these peptides has not been established. Three major types of endocrine cell have been identified in human fetal lung (types 1, 2 and 3), a distinction based largely on the morphology of their secretory granules which are 110-200 nm in diameter¹². Granules in the type-2 cell of the lung resemble those in P cells of the gut and pancreas¹⁹. The P-cell product has not been identified but it may be a bombesin-like peptide ²⁰. Bombesin is a tetra-decapeptide isolated from frog skin ²¹ having a wide range of actions on the mammalian gastrointestinal tract and vasculature²². The similarity between P cells of the gut and certain granulated cells of the lung suggested that a bombesin-like peptide might be present in the human lung, and we report here the presence of bombesin-like immunoreactivity in human fetal and neonatal lung.