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.