EPIDERMAL LIPID IN SEVERAL CETACEAN SPECIES - ULTRASTRUCTURAL OBSERVATIONS

The ultrastructure of the skin of four cetacean species, bottlenose do lphin (Tursiops truncatus) long-finned pilot whale (Globicephala melae na), humpback whale (Megaptera novaeangliae), and fin whale (Balaenopt era physalus) was investigated with particular reference to epidermal lipid. It has already been established that massive lipid reservoirs e xist in whales, that the biochemical structures of cetacean lipids are unique, and that unusual intracellular lipid droplets appear in the e pidermis. We report here some novel findings on scanning electron micr oscopic morphology of epidermal lipid, and on its ultrastructural morp hology in general and specialized integumentary sites, including speci es not previously investigated. The intracellular epidermal lipid drop lets were more extensive than lamellar body-derived intercellular lipi d which is within the interstices of stratum externum cells. The intra cellular droplets were spherical, highly variable in size ranging from 0.24 mum to 3.0 mum in diameter, appeared singly or were aggregated i n cytoplasmic cavitations, and often were closely associated with epid ermal cell nuclei. Evidence for exocytosis of the intracellular drople ts was not observed. Significant numbers of intracellular lipid drople ts are not observed in the epidermis of terrestrial mammals, so their presence is one of several aquatic specializations of the cetacean int egument. Its full significance remains obscure, but it is more probabl y associated with epidermal cell metabolism than with secretion of lip id.