Involvement of the lodothyronines in liver and hepatoma cell proliferation in the rat.

3,3',5-Triiodo-L-thyronine (200 microgram/100 g) is shown to be a potent liver parenchymal cell mitogen in the rat, and thyroidectomy is seen to severely inhibit hepatocyte proliferation in regenerating rat liver. Taken together, these observations point to a crucial role for the iodothyronine in liver cell hyperplasia. The growth rates of the transplantable Morris hepatomas 7777 and 5123tc are shown to be retarded in the surgically thyroidectomized-parathyroidectomized rat. This inhibition of tumor growth can be reversed by thyroid hormone administration. It has earlier been observed that the hypothyroid state induced in the rat by administration of propylthiouracil or radioactive iodine retarded the growth of the transplanted Morris hepatomas 7800 and 44, suggesting that these tumors were also thyroid dependent. Our results suggest that the thyroid hormones may play a similar role in the growth of liver cell-derived cancers as they do in normal hepatocyte proliferation.