Fat distribution in the skin of bottlenose dolphins (Tursiops truncatus and Tursiops gilli)

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Abstract
Frozen sections stained with Oil‐red‐O and semithin (0.5 μm) plastic sections stained with toluidine blue revealed an abundance of fat globules of various sizes in all strata of the epidermis of bottlenose dolphins (Tursiops truncatus and T. gilli). The fat was rather evenly distributed but sometimes appeared as circumscribed areas of heavier concentration involving hundreds of cells (as seen in a single plane). Occasionally, there were smaller groups of epidermal cells heavily loaded with lipid. The dermis presented a unique phenomenon in the presence of abundant extracellular fat distributed among the collagen bundles as droplets of various sizes or as larger, irregularly shaped lipid particles that seemed to conform to the spaces between collagen bundles. These lipid particles were sometimes seen to be closely applied to the dermal surface of the stratum basale. Equally unusual was the presence of lipid particles of various sizes and shapes in the lumen of some of the vessels of the dermal papillae. Granular cells resembling mast cells were commonly seen in the papillary dermis and some were closely associated with lipid particles. Blood vessels of the reticular dermis tended to have collections of lipid droplets in the loose connective tissue often found adjacent to the tunica adventitia. It is postulated that the extracellular dermal lipids (probably mainly triglycerides) are broken down to free fatty acids that diffuse into the basal layer of the epidermis and are there resynthesized into triglycerides. Possible uses for the epidermal lipids are discussed.

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