Hormonal regulation of DNA polymerase-β activity in the rat thyroid gland

Abstract

ABSTRACT Using hypophysectomized rats, it has been shown that DNA polymerase-β activity in the adrenal gland and testis is largely influenced by pituitary trophic hormones. Sucrose gradient centrifugation of thyroid extracts revealed three peaks of DNA polymerase-β activity sedimenting at 3·3S, 7·3S and 12S. Of these, hypophysectomy induced a decrease in the 3·3S DNA polymerase-β, whereas other molecular forms were affected only slightly. DNA polymerase-α and -γ activities were unaffected by hypophysectomy. These changes in DNA polymerase-β caused by hypophysectomy were reversed by daily i.p. injection of TSH. Furthermore, stimulation of the thyroid by excess TSH induced by the administration of 1-methyl-2-mercaptoimidazole resulted in an increase of all forms of thyroid DNA polymerase-β. These results show that the level of DNA polymerase is relatively constant after hypophysectomy but that DNA polymerase-β in the rat thyroid gland is also modulated by TSH mainly through the change of activity of the polymerase-β which sediments at 3·3S. J. Endocr. (1988) 119, 303–308