title: Vitamin D metabolism in the hooded seal (Cystophora cristata).
abstract: Fish-eating mammals, such as seals, appear to ingest levels of vitamin D that are toxic to most mammals. To determine how seals cope with high vitamin D intakes, the metabolism of tritiated cholecalciferol ([3H]D3) was investigated in hooded seal (Cystophora cristata) pups during their postweaning fast and pups and adults consuming herring alone or supplemented with 400,000 iu D3 daily. [3H]D3 was metabolized to 25-[3H]OHD3 and 24,25-[3H](OH)2D3. 1,25-[3H](OH)2D3 was not detected, but plasma levels of 1,25-(OH)2D were similar to those in other mammals and were not affected by vitamin D intake. Plasma vitamin D, 25-OHD and 24,25-(OH)2D increased with vitamin D intake, but 25-OHD did not increase to the extent seen in other mammals. The supplemented seals showed no evidence of toxicity. Levels of 24,25-(OH)2D were higher in the unsupplemented seals (4 to 33 ng/mL) than reported in other mammals with similar 25-OHD levels and did not decrease with 25-OHD. High levels of 24,25-(OH)2D relative to 25-OHD have also been found in hooded seals in the wild. The half-lives of vitamin D, 25-OHD and 24,25-(OH)2D were shorter than those reported for most other mammals. Increased conversion of 25-OHD to 24,25-(OH)2D and a high capacity for vitamin D storage in their large blubber mass appeared to be factors in the resistance of seals to vitamin D toxicity.
authors.affiliation: Department of Zoology, College of Biological Science, University of Guelph, Ontario, Canada.
authors.forename: K M
authors.initials: KM
authors.lastname: Keiver
authors.forename: H H
authors.initials: HH
authors.lastname: Draper
authors.forename: K
authors.initials: K
authors.lastname: Ronald
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000378:metabolism; D010872:Caniformia / Q000378:metabolism*; D002762:Cholecalciferol / Q000097:blood / Q000378:metabolism; D004032:Diet; D005243:Feces / Q000032:analysis; D006207:Half-Life; D006887:Hydroxycholecalciferols / Q000378:metabolism; D007408:Intestinal Absorption; D046048:Seals, Earless / Q000378:metabolism*; D014807:Vitamin D / Q000378:metabolism* / Q000633:toxicity
chemical_list: D006887:Hydroxycholecalciferols; D014807:Vitamin D; D002762:Cholecalciferol; D002117:Calcitriol