The regulatory role of tri-iodothyronine on the production of alpha-fetoprotein and albumin by mouse fetal liver cells.

The purpose of this study was to assess possible effects of tri-iodothyronine (T3) on the production of alpha fetoprotein (AFP) and albumin by mouse fetal liver cells. AFP from serum-free conditioned media of TIB73 mouse fetal liver cells was measured by immunoradiometric assay and albumin was measured by chromogenic assay. The expression of mRNAs was quantified by Northern blotting analysis. A marked inhibition of AFP secretion was found as well as an increase in albumin produced by T3 in a dose-dependent manner. The effects of T3 AFP and albumin secretion paralleled the effects of T3 on the steady-state expression of mRNAs encoding albumin and AFP. These data may point to a possible role of T3 in the transcriptional switch from AFP to albumin during fetal development and may explain the observation of high levels of AFP in cases of congenital hypothyroidism.