T3 stimulates the synthesis of a specific mRNA in primary hepatocyte culture.

The mechanism of triiodothyronine (T3) induction of a thyroid hormone responsive mRNA (mRNAS14) was studied in primary cultures of adult rat hepatocytes. T3 induced mRNAS14 in less than one hour after addition to the cultures. After 24 hours exposure to T3, the level of mRNAS14 was 2.5 to 6 times above the untreated controls. Addition of Actinomycin-D to both induced and control cultures led to similar mRNAS14 disappearance curves, implying that T3 augments the synthesis of mRNAS14 rather than stabilizing pre-formed mature mRNA. Glucagon inhibits the T3 induction of mRNAS14. When added to both induced and control cultures, glucagon leads to similar fractional decay curves for mRNAS14, confirming the Actinomycin-D studies. These findings demonstrate T3 induces mRNAS14 directly in the hepatocyte by increasing the synthesis of the mature mRNA.