Localization of porphyrin in mouse Harderian glands

Lipid secreting Harderian glands in the ocular region of rodents contain a large amount of metal-free porphyrins. The localization of these porphyrins and the areas of formation of the lipidporphyrin complexes in the glandular lumina have not been clearly defined. We therefore examined the intracellular localization of porphyrin fluorescence both in tissue sections and in cultured cells of Harderian glands of 5 weeks old female ICR mice, using confocal UV-laser scanning microscopes. The fluorescence appeared in glandular cells containing lipid droplets, but not in non-glandular cells (e.g. myoepithelial or interstitial) without these droplets. Fluorescence in the cells was recognized in the cytoplasm, but there was no evidence indicating that porphyrins were restrictively stored in mitochondria. Nuclei and lipid droplets lacked fluorescence. It is thus reasonable to conclude that porphyrins accumulate in the cytoplasm, and that porphyrins and lipids are secreted separately from glandular cells. The lipid-porphyrin complex is therefore probably formed in the glandular lumina and not within the glandular cells.