DNA synthesis in isolated mitochondria: effect of thyroidectomy and of triiodothyronine administration in vivo.

The incorporation was studied of labelled deoxy-ribonucleosides triphosphates into acid-insoluble material by isolated liver mitochondria, obtained from either normal young male rats, or thyroidectomized at weaning, or thyroidectomized and then treated with triiodothyronine (T3). The incorporation extents in normal animals decreased with the age starting from the weaning until the 210th day. Thyroidectomy reduced the incorporation extent to about 70% of the values observed in normal animals. During the T3 treatment of thyroidectomized rats a sharp increase of incorporation was observed one day after the first administration, followed by a decrease from the 1st to the 3rd day; successively the incorporation extent remained unchanged until the 12th day. Finally, evidence was provided that T3 doses used were thyreomimetic and definitely lower than the thyreotoxic ones.