Thyroid hormone receptors in brain and liver during ageing.

The binding properties--binding capacity (MBC) and affinity (Ka)--of T3 nuclear receptors were analyzed in cortex, cerebellum and liver of rats aged 3, 6, 12 and 24 months. A slight but not significant decrease of Ka was observed in different tissues of normal rats. In hypothyroid animals the Ka in cortex at 24 months was significantly lower than at 3 months. During ageing the MBC of brain receptors decreased whereas hepatic receptors were not altered. Hypothyroidism did not further affect the MBC of the receptors. The data indicate that during ageing the T3 nuclear receptors behave differently in brain and liver. The difference in MBC suggests selectivity in organ sensitivity to thyroid hormones.