The house musk shrew, Suncus murinus as unique laboratory animal model for estimation of thyroid hormone function

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1) The house musk shrew Suncus murinus belongs to the most primitive mammalian oder Insectivora. This species is widely distributed in hot climate area from East Africa to East Asia2) We found that the type-1 iodothyronine deiodinase (D1) activity in shrew liver was one third of that in the rat liver. The other hand, D2 activity was higher level. To elucidate the mechanism for those activities, we cloned the D1 and D2 cDNA from the shrew liver. RT-PCR was performed using different sets of primers, which were designed based on conserved amino acid sequences of the D1, D2 and D3 among different species. The cloned cDNAs contain the entire open reading frame. A putative selenocystein (Sec) was identified, which is conserved among mammalian species. Cloned the D1 and D2 cDNA from the shrew were comparable same to other mammal species3) Blood T3 level in the shrew was stable at the fasting status, but T3 level in the mouse and rat was decreased. D1 mRNA in the liver and D2 mRNA in the brown adipose tissue were reduced but D2 activities in the brain were incresed. Brain D2 activities may support normal blood T3 level in the shrew4) Blood T3 level in the shrew was constant in fasting status and basic metabolism was not reduced in fasting status. So, the shrew is soon died in fasting status. The shrew is so unique animal to study the mechanism of thyroid hormone metabolism comparable to the rats and mice