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 cells10,11, and possess APUD cell characteristics10-13. 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-hydroxytryptamine10,14 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 peptide16,17 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.
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