Induction of type III-deiodinase activity in astroglial cellsby retinoids

Thyroid hormones and retinoic acid (RA) are important modulators of growth, development, and differentiation. The effects of retinoids on type III deiodinase (D-III) activity were examined in astroglial cells cultured in a chemically defined medium devoid of hormones and growth factors. Incubation of astroglial cells with 5 micromolar all-trans-RA caused up to 200-fold increase in D-III activity, which reached a plateau after 48 h. All-trans-RA (5 uM) had little or no effect on type II deiodinase, the enzyme which catalyzes the activation of thyroxine to 3,5,3'-triiodothyronine.