Ultrastructural similarity of endocrine-like cells of the human lung and some related cells of the gut.

Abstract

The ultrastructure of endocrine-like cells of the human lung was compared to the ultrastructure of endocrine-like cells of the stomach and pancreas in both adult and foetal material. Three types of endocrine-like cells were found in the human foetal lung. Type 1 or P1 cells contained very small granules (about 110 nm) of two varieties, cored and vesicular; type 2 or P2 cells with cored granules measuring about 130 nm; and type 3 cells with cored granules of about 180–190 nm. In the adult lung only one type Pa cells with cored granules could be found. Cells resembling foetal P1 cells were not found in foetal or adult gastric mucosa, or in the pancreas. In the gastric mucosa cells resembling pulmonary Pa or P2 cells were moderately represented and often difficult to distinguish from each other. Thus, they were grouped together as gastric P cells. Cells with granules resembling those of pulmonary type 3 cells were found most numerous in the adult oxyntic mucosa. Cells resembling gastric P cells (and pulmonary P2 cells) were rather numerous in foetal pancreas, but very rare in adult pancreas. Few cells containing granules somewhat resembling those of pulmonary type 3 cells were present in both foetal and adult pancreas. The results were discussed in respect to 1) the similarities between some gastric or pancreatic carcinoids and lung carcinoids, 2) the gastro-pancreatic P cells as a separate cell population, 3) the possible secretion by the lung endocrine-like cells of active substances, either amines or peptides, 4) the similarity between the secretory granules of Pa and P1 cells and neurosecretory granules of the hypothalamus and between P2 cells and some endocrine cells of the pituitary.