Immunocytochemical correlation of peptides and tyrosine hydroxylase in nerve fibres of the human parotid gland.

The peptidergic innervation of parenchymal and vascular components in the human parotid gland was investigated by double-labelling fluorescence. Peptide immunoreactivity in nerve fibres was correlated with the presence of tyrosine hydroxylase (TH). By light microscopy, acinar innervation consisted of fibres with the combinations neuropeptide Y (NPY)/TH and NPY/vasoactive intestinal polypeptide (VIP). Some fibres were solely NPY, TH or VIP immunoreactive. Rarely, substance P (SP)/calcitonin gene-related (CGRP)-immunolabelled fibres were associated with acini. Intercalated ducts were often approached by NPY/TH- and VIP-containing fibres. VIP innervation of excretory ducts was sparse. Intralobular and intralobar excretory ducts, in addition to NPY and TH, revealed CGRP and CGRP/SP innervation, whereas nerve fibres on interlobar excretory ducts very rarely contained NPY and none of the other mediators. Vascular innervation consisted of NPY/TH and SP/CGRP fibres; in a few fibres SP was colocalized with leu-enkephalin. Large arteries were encircled by some VIP-positive fibres. The findings suggest a specific participation of neuropeptides and of peptide combinations in the regulation of parotid exocrine function.