title: Brown adipose tissue in cetacean blubber.
abstract: Brown adipose tissue (BAT) plays an important role in thermoregulation in species living in cold environments, given heat can be generated from its chemical energy reserves. Here we investigate the existence of BAT in blubber in four species of delphinoid cetacean, the Pacific white-sided and bottlenose dolphins, Lagenorhynchus obliquidens and Tursiops truncates, and Dall's and harbour porpoises, Phocoenoides dalli and Phocoena phocoena. Histology revealed adipocytes with small unilocular fat droplets and a large eosinophilic cytoplasm intermingled with connective tissue in the innermost layers of blubber. Chemistry revealed a brown adipocyte-specific mitochondrial protein, uncoupling protein 1 (UCP1), within these same adipocytes, but not those distributed elsewhere throughout the blubber. Western blot analysis of extracts from the inner blubber layer confirmed that the immunohistochemical positive reaction was specific to UCP1 and that this adipose tissue was BAT. To better understand the distribution of BAT throughout the entire cetacean body, cadavers were subjected to computed tomography (CT) scanning. Resulting imagery, coupled with histological corroboration of fine tissue structure, revealed adipocytes intermingled with connective tissue in the lowest layer of blubber were distributed within a thin, highly dense layer that extended the length of the body, with the exception of the rostrum, fin and fluke regions. As such, we describe BAT effectively enveloping the cetacean body. Our results suggest that delphinoid blubber could serve a role additional to those frequently attributed to it: simple insulation blanket, energy storage, hydrodynamic streamlining or contributor to positive buoyancy. We believe delphinoid BAT might also function like an electric blanket, enabling animals to frequent waters cooler than blubber as an insulator alone might otherwise allow an animal to withstand, or allow animals to maintain body temperature in cool waters during sustained periods of physical inactivity.
authors.affiliation: Kitasato University School of Veterinary Medicine, Towada, Aomori 034-8628, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Hashimoto
authors.affiliation: Kitasato University School of Veterinary Medicine, Towada, Aomori 034-8628, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Ohtsuki
authors.affiliation: Kitasato University School of Veterinary Medicine, Towada, Aomori 034-8628, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Kakizaki
authors.affiliation: Kitasato University School of Veterinary Medicine, Towada, Aomori 034-8628, Japan.
authors.forename: Kento
authors.initials: K
authors.lastname: Amou
authors.affiliation: Kitasato University School of Veterinary Medicine, Towada, Aomori 034-8628, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Sato
authors.affiliation: Kitasato University School of Veterinary Medicine, Towada, Aomori 034-8628, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Doi
authors.affiliation: The University Museum, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Sara
authors.initials: S
authors.lastname: Kobayashi
authors.affiliation: Faculty of Fisheries Sciences, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan.
authors.forename: Ayaka
authors.initials: A
authors.lastname: Matsuda
authors.affiliation: Kitasato University School of Veterinary Medicine, Towada, Aomori 034-8628, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Sugiyama
authors.affiliation: Division of Applied Biosciences, Kyoto University Graduate School of Agriculture, Kitashirakawa Oiwakecho, Kyoto 606-8502, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Funaba
authors.affiliation: Faculty of Fisheries Sciences, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsuishi
authors.affiliation: Enoshima Aquarium, Fujisawa, Kanagawa 251-0035, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Terasawa
authors.affiliation: Kitasato University School of Veterinary Medicine, Towada, Aomori 034-8628, Japan.
authors.forename: Junji
authors.initials: J
authors.lastname: Shindo
authors.affiliation: The University Museum, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Endo
mesh_terms: D002001:Adipose Tissue, Brown / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000502:physiology; D000818:Animals; D001833:Body Temperature Regulation; D004289:Dolphins / Q000033:anatomy & histology* / Q000378:metabolism / Q000523:psychology; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D050151:Subcutaneous Fat / Q000000981:diagnostic imaging / Q000378:metabolism / Q000502:physiology; D014057:Tomography, X-Ray Computed; D000071256:Uncoupling Protein 1
chemical_list: D007473:Ion Channels; D024101:Mitochondrial Proteins; D000071256:Uncoupling Protein 1