Study on the mechanisms of vitamin A-storage in arctic animals

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As xenobiotics may reduce the threshold of vitamin A-toxicity and both vitamin A and fatsoluble xenobiotics have a tendency to accumulate in the food chain, we have perfomied a systematic characterization of the hepatic vitamin A-storage in mammals and birds of the Svalbard archipelago and searched for sign of vitamin A-related toxicity in these animals. The top predators including polar bear, arctic fox, bearded seal and glaucous gull contained about 10-20 times more vitamin A than all other arctic animals studied as well as their genetically related continental top predators. The values are also high compared to normal human and experimental animals like mouse and rat. This massive amount of hepatic vitamin A was located in large autofluorescent lipid droplets in hepatic stellate cells. The droplets made up most of the cells' cytoplasm. The development of such an efficient vitamin A-storing mechanism in the hepatic stellate cells may have contributed to the survival of top predators in the extreme environment of the Arctic. These animals demonstrated neither sign of hypervitaminosis A nor pathological findings in the liver.Kidney total retinol, which may be used as a biomarke for vitamin A-related toxicity or excess, in polar bear and bearded seal were below 1% of their liver value, Which is in the normal range for most animals. Arctic fox and glaucous gull, however, had kidney levels of about 9 and 42% of the liver values, respectively. This increased kidney concentrations of total retinol in arctic fox and glaucous gull is most likely a sign of vitamin A-toxicity that deserved attention. This observation is alarming and has not been observed previously in free-living animals. Analysis of samples from older predators who over time may have accumulated more of vitamin A and organic pollutants may clarify whether these and other signs of vitamin Atoxicity is present in such animals.