AGING DECREASES RETINOIC ACID AND TRIIODOTHYRONINE NUCLEAR EXPRESSIONIN RAT-LIVER - EXOGENOUS RETINOL AND RETINOIC ACID DIFFERENTIALLY MODULATE THIS DECREASED EXPRESSION

The expression of nuclear receptors of retinoic acid (RAR) and triiodo thyronine (TR) was analyzed in the liver of rats aged 2.5 (young), 6 ( adult) and 24 (aged) months. In aged rats, decreased binding propertie s, binding capacity (C-max) and affinity (K-a), of nuclear receptors w ere observed. This resulted, at least in part, from decreased transcri ption of receptor genes in that the amount of their mRNA also decrease d. Moreover, the activity of malic enzyme (ME) and tissue transglutami nase (tTG), whose genes are TR and RAR responsive, respectively, was r educed in aged rats. These results are in agreement with the decreased binding capacity of these receptors. An inducer-related increase of R AR and TR expression was observed 24 h after a single dose of retinoic acid administration (5 mg/kg), while retinol administration (retinyl palmitate, 13 mg/kg) was without incidence on nuclear receptor express ion in aged rats. (C) 1997 Elsevier Science Ireland Ltd.