TERMINAL DIFFERENTIATION OF MOUSE PREADIPOCYTE CELLS - ADIPOGENIC ANDANTIMITOGENIC ROLE OF TRIIODOTHYRONINE

The role of triiodothyronine (T-3) in the differentiation process of O b1771 mouse preadipocyte cells has been studied under serum-free and h ormone supplemented culture conditions which were previously shown to lead to terminal differentiation. In the absence of T-3, a dramatic de crease in the adipogenic activity of the culture medium (EC(50) = 0.1 nM) could be observed, as indicated 12 days after confluence by the lo w levels of late markers of differentiation such as adipsin, lipid-bin ding protein aP2 and glycerol-3-phosphate dehydrogenase as well as the sharp reduction of the number of triacyglycerol-containing cells. Thi s decrease in adipogenic activity was accompanied by a parallel increa se of the mitogenic potency of the culture medium. Therefore, T-3 appe ars to be a hormone capable of modulating both proliferation and diffe rentiation of preadipocytes. T-3 ceased to be necessary provided the c ulture medium was supplemented with high concentrations of inducers of differentiation, such as 8-bromo-cAMP or carbaprostacyclin.