Keiver K M, Draper H H, Ronald K
Department of Zoology, College of Biological Science, University of Guelph, Ontario, Canada.
J Nutr. 1988 Mar;118(3):332-41. doi: 10.1093/jn/118.3.332.
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 24,25-3H2D3. 1,25-3H2D3 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.
以鱼为食的哺乳动物，如海豹，摄入的维生素D水平似乎对大多数哺乳动物具有毒性。为了确定海豹如何应对高维生素D摄入量，研究了带帽海豹（Cystophora cristata）幼崽在断奶后禁食期间以及单独食用鲱鱼或每天补充400,000国际单位维生素D3的幼崽和成年海豹体内氚标记胆钙化醇（[3H]D3）的代谢情况。[3H]D3代谢为25-[3H]OHD3和24,25-3H2D3。未检测到1,25-3H2D3，但血浆中1,25-(OH)2D的水平与其他哺乳动物相似，且不受维生素D摄入量的影响。血浆维生素D、25-OHD和24,25-(OH)2D随维生素D摄入量增加而升高，但25-OHD的升高幅度不如其他哺乳动物。补充维生素D的海豹没有出现中毒迹象。未补充维生素D的海豹体内24,25-(OH)2D的水平（4至33纳克/毫升）高于其他25-OHD水平相似的哺乳动物，且不随25-OHD水平下降。在野生带帽海豹中也发现相对于25-OHD而言24,25-(OH)2D水平较高。维生素D、25-OHD和24,25-(OH)2D的半衰期比大多数其他哺乳动物报道的要短。25-OHD向24,25-(OH)2D的转化率增加以及它们大量脂肪中储存维生素D的能力较强，似乎是海豹对维生素D毒性具有抗性的因素。
