HEPATIC POLY(ADP-RIBOSE) POLYMERASE-ACTIVITY IN RAT IS CONTROLLED BY THYROID-HORMONES

The in vivo effect of the thyroidal state on poly(ADP-ribose) polymera se activity was investigated in eu- and hypothyroid rats after treatme nt with L-triiodothyronine. Untreated hypothyroids showed an increased basal rate of the enzyme. The treatment of both eu- and hypothyroid r ats with L-triiodothyronine induced a prompt drop of the endogenous ac tivity 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 vit ro exposure to increasing L-triiodothyronine concentrations from 10(-1 8) to 10(-6) M resulted in a progressive inhibition of the enzyme. Thi s loss in activity was not derived from a reduction of the total level of the catalytic protein. The pretreatment with the antagonist amioda rone suppressed the hormone effect,suggesting that nuclear receptors c ould mediate poly(ADP-ribose) polymerase activity. (C) 1994 Academic P ress, Inc.