[Chronobiological patterns of the action of thyroxine on cell reproduction in Ehrlich ascites tumor]

Experiments on white random-bred male mice were made to study the effect of L-thyroxine on cell proliferation of the hyperdiploid strain of Ehrlich's ascites carcinoma. It was shown that upon prolonged thyroxine administration (during 6 days of carcinoma growth) the action of the latter appeared dose-dependent. The doses used were 1, 10, 30, 60, 100 micrograms/100 g bw. Circadian rhythms were noted in the sensitivity of the dividing cells to the hormone applied in a dose of 10 micrograms/100 g bw as was a certain decrease in the total level of the mitotic activity. At the same time thyroxine did not exert any noticeable effect on the average daily magnitudes of the number of DNA-synthesizing cells and did not change the pattern of modulations in the radioactive index. The changes in the mitotic index and radioactive index were asynchronous in control and experimental animals.