Age-related changes in thyroid hormone responsive protein (THRP) expression in cerebral tissue of rats

To determine if aging in rats is associated with insensitivity of cerebral tissue to thyroid hormones (TH), the expression of a TH responsive protein or (THRP) in cerebral tissue was studied in male Fischer rats at 4, 12 and 24 months of age during euthyroid, hypothyroid and hyperthyroid states. The basal levels of THRP mRNA was significantly increased in 24-month-old and in 12-month-old rats while THRP mass measured by Western blots was decreased compared to 4-month-old rats. Compared to euthyroid rats, hyperthyroidism in 4-month-old rats was associated with 5.1-fold increase in THRP mRNA and 3.7-fold increase in protein content while in hyperthyroid aged rats, the increase of THRP mRNA was only 1.6-fold and the increase in the protein was 2.4-fold. Hypothyroidism did not significantly alter THRP or its mRNA in either young or aged rats. It is concluded that aging in rats is associated with reduced cerebral tissue responsiveness to thyroid hormones.