STIMULATION OF INCORPORATION BY TRIIODOTHYRONINE OF THYMIDINE-METHYL-3H INTO HEPATIC DNA OF RAT

Administration of single dose of triiodothyronine (T3) results in hepatic cell proliferation as judged by the mitotic index and the enhanced thymidine-methyl-3H or orthophosphate-32P incorporation into DNA. Increased mitoses could be observed 24 hours after T3 administration; 72 hours after the hormone injection, binuclear cells were abundant. The enhanced hepatic DNA synthesis reached its peak 24-48 hours after T3 injection. Radioautographic techniques revealed that T3 increases DNA synthesis primarily in the hepatic cells. T3 had no effect on testicular DNA synthesis. T3-induced liver DNA synthesis was sensitive to the inhibitory effects of actinomycin D and cycloheximide. The present observations indicate that the early effects of thyroid hormone on liver protein and RNA synthesis initiates DNA synthesis, which in turn leads to the increased proliferation of hepatic tissue. © 1968.