IODOTHYRONINE DEIODINASES IN A MAMMALIAN HIBERNATOR, THE CHIPMUNK (TAMIAS-ASIATICUS)

We examined the activities of iodothyronine deiodinase, a key enzyme f or thyroid hormone metabolism, in selected tissues of the chipmunk (Ta mias asiaticus), a mammalian hibernator, of both sexes in the summer s eason. Reverse T-3 5'-deiodinase (5'-D) activity was the highest in th e liver followed by the kidney; T-4 5'-D activity was the highest in b rown adipose tissue (BAT) and T-3 5-deiodinase (5-D) activity was the highest in the testes followed by the brain. Distributions of three ty pes of deiodinase activities in liver, kidney, BAT, and brain were com parable to other mammals reported, except that the type III deiodinase was unique in testes. The 5'-D activity of liver and kidney of chipmu nks was 52% and 24%, respectively, of male rats and the 5-D activity o f brain and testes of chipmunks was 227% and 567%, respectively, of ma le rats. In addition, the cold exposure increased BAT 5'-D activity in chipmunks as reported in the ground squirrels. Our results indicated that tissue distribution of deiodinases and response to cold exposure in BAT in hibernators are similar to nonhibernators. However, there wa s a quantitative difference of rT(3) 5'-D and T-3 5-D activities in so me tissues between chipmunks and rats, indicating different local thyr oid hormone metabolisms in hibernators and nonhibernators. (C) 1997 El sevier Science Inc.