Hepatic Poly(ADP-Ribose) Polymerase Activity in Rat Is Controlled by Thyroid Hormones

Abstract

The in vivo effect of the thyroidal state on poly(ADP-ribose) polymerase activity was investigated in eu- and hypothyroid rats after treatment with L-triiodothyronine. Untreated hypothyroids showed an increased basal rate of the enzyme. The treatment of both eu- and hypothyroid rats with L-triiodothyronine induced a prompt drop of the endogenous activity not due to a reduction of the catalytic protein. This decrease well evident 1 h after treatment was transient, returning to controls values within 8 h. In isolated liver nuclei from euthyroids the in vitro exposure to increasing L-triiodothyronine concentrations from 10−18 to 10−6 M resulted in a progressive inhibition of the enzyme. This loss in activity was not derived from a reduction of the total level of the catalytic protein. The pretreatment with the antagonist amiodarone suppressed the hormone effect,suggesting that nuclear receptors could mediate poly(ADP-ribose) polymerase activity.