Uptake of L-dopa and L-5-hydroxytryptophan by endocrine-like cells in the rat larynx

Synopsis In the larynx of the rat, and to a lesser extentin the trachea and main bronchi, there are numerous cells which possess the amine-handling characteristics, but not the enzymatic ones, of the APUD series of endocrine polypeptide cells. The cytochemical properties of their contained granules, which are ultrastructurally atypical in reaching sizes up to 2000 nm on their longest axis, are not those of the APUD series since their protein is predominantly basic and arginine-rich, rather than acidic.A weak formaldehyde-induced autofluorescence is present in the cells, due to a substance with an excitation maximum at 400 nm and an emission maximum at 490 nm. This may be dopamine.The true nature of these endocrine-like cells is not apparent. They are regarded, for the present, as being related to cutaneous melanocytes.