Immunocytochemical Demonstration of the Co-storage of Noradrenaline with Met-enkephalin-Arg6-Phe7 and Met-enkephalin-Arg6-Gly7-Leu8 in the Carotid Body Chief Cells of the Dog

Cellular and ultrastructural localization of catecholamines in the dog carotid body was investigated by peroxidase-antiperoxidase method for light microscopy and by protein A-colloidal gold technique for electron microscopy, and compared with that of preproenkephalin A-related opioid peptides, i.e., Met-enkephalin-Arg6-Phe7 (Met-Enk-Arg-Phe) and Met-enkephalin-Arg6-Gly7-Leu8 (Met-Enk-Arg-Gly-Leu). Immunocytochemistry at the light microscopic level using consecutive semi-thin sections of Araldite-embedded tissue showed that some 30% of the chief cells contained immunoreactive noradrenaline together with Met-Enk-Arg-Phe and Met-Enk-Arg-Gly-Leu. A considerable number of chief cells exhibited immunoreactivities representing one or two of these three kinds of substances. A few chief cells showed none of the specific immunoreactivities. Immunoreactive adrenaline was not demonstrated in any cells of the dog carotid body. At the electron microscopic level, co-existence of noradrenaline with Met-Enk-Arg-Phe or Met-Enk-Arg-Gly-Leu in the same secretory granules was shown using the double labeling protein A-colloidal gold technique. Possible interactions of catecholamines and opioid peptides deserve consideration for the understanding of the chief cell's role in the carotid body chemoreceptor.