Effect of streptozotocin-induced diabetes mellitus on type 1 deiodinase (D1) in inherited D1-deficient mice

We investigated the effects of streptozotocin (STZ)-induced diabetes on thy roid hormone levels, type 1 deiodinase (D1) activity and messenger RNA (mRN A) levels in inherited D1 deficient C3H mice in a comparative manner with c ontrol C57 mice. The apparent maximum velocity (V-max) D1 values in C3H mic e were 3% (liver) and 26% (kidney) of those in C57 mice. In C3H mice, simil ar serum T3, slightly higher T4, and 2.6-fold higher rT3 levels were observ ed compared with C57 mice. In STZ-induced diabetes, serum T4 level markedly decreased in both C3H and C57 mice. Serum T3 levels in STZ-C3H mice simila rly decreased as in STZ-C57 mice. On the other hand, serum rT3 levels incre ased to 3.3-fold higher in STZ-C3H than in STZ-C57 mice. The V-max values w ere decreased to 12% (STZ-C3H) and to 30% (STZ-C57) in liver, and decreased to 33% (both STZ-C3H and STZ-C57) in kidney. The changes in D1 mRNA levels in diabetes versus control were comparable to those of D1 activities in bo th strains. In summary, similar mechanism(s) to those which decrease the D1 expression and the serum T3 level in diabetes, function in D1 deficient C3 H mice as in C57 mice. It appears that hepatic and renal D1 activity alone can not explain the similar reduction in T3 level in STZ-C3H mice and STZ-C 57 mice.