To determine the relationship between the concentrations of serum T3and hepatic nuclear T3receptor in a reversible nonthyroidal disease, we studied these parameters in rats with streptozotocin-induced diabetes mellitus, control rats, and rats that were weight-matched to the diabetic rats by food restriction. Results were similar either 1 or 9 weeks after the induction of diabetes. A significant decrease from control in mean serum T4 T3and free T3index was noted in the diabetic rats. However, mean serum TSH was not altered significantly. The hepatic nuclear T3-binding capacity in the diabetic rats was similar to that in the control at both time intervals, whereas the nuclear T3-binding capacity of fasted rats was decreased. The dissociation of serum T3 and hepatic nuclear receptor concentrations in diabetic rats suggests that receptor concentration is not modified by thyroid hormones in this nonthyroidal disease.
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