Distribution of Met-enkephalyl-Arg-Gly-Leu in rat larynx: partial coexistence with vasoactive intestinal polypeptide, peptide histidine isoleucine and neuropeptide Y.

Using light microscopic (LM) enzyme-immunohistochemistry on deparaffinized adjacent sections Met-enkephalyl-Arg-Gly-Leu (ME-RGL) immunoreactivity was found to partially coexist with immunoreactive neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine (PHI) in intrinsic laryngeal neurons of the rat. Further ME-RGL-immunoreactive (ir) fibres were found around glands in the subepithelium, in connective tissue of striated muscle and in the perichondrium, as well as around arterial and venous blood vessels. They frequently contacted mast cells and macrophages. The presence of ME-RGL indicates pro-enkephalin-related origin of this novel laryngeal opioid system. From the specific target relations and close interrelations of fibres staining for opioids with those staining for the other peptides--which are known to be more or less characteristic of the sympathetic (NPY), parasympathetic (VIP, PHI) and sensory (calcitonin gene-related peptide; CGRP) subdivisions of the peripheral nervous system--we deduce that opioid/non-opioid interactions might co-control various laryngeal functions, e.g. glandular secretion, blood flow, immune and inflammatory responses and/or might be of relevance in trophic mechanisms.