Thyroid influence on the growth of hepatoma HW-165 in Wistar rats

The development of a fast-growing hepatoma (HW-165) in normal euthyroid Wistar rats, was shown to be stimulated by daily injection of a dose of triiodo-L-thyronine (T3) as low as 1.5 microgram/100 g body weight. Administered to thyroidectomized rats, T3 completely restored the frequency of tumor initiation and accelerated the growth of the hepatoma, which had been considerably slowed down in hypothyroid rats. Contrary to other investigators, working on fast-growing Morris hepatomas, we did not observe any significant increase in the T3 level in the serum of hepatoma HW-165-bearing rats. Similarly, the tetra-iodo-L-thyronine (T4) levels were of the same order of magnitude in the blood of both normal and tumor host animals. The mitotic activity was reduced in hepatomas transplanted in hypothyroid rats and increased in tumors of T3-treated animals. These results support the assertion of Short (20) suggesting a relationship between the mitogenic effects of iodothyronines on the normal hepatocyte and on transplanted tumors of hepatic origin.