Figure 2.

Dog thyrocytes are sensitive to TGFβ₁ inhibition during G1. (●) Quiescent 4-day-old dog thyrocytes were stimulated at 0 h with TSH (1 mU/ml) in the presence of BrdU and the cumulative BrdU-labeling index was determined at the indicated times. (○) At the indicated times after TSH administration at 0 h in the presence of BrdU, TGFβ₁ (2 ng/ml) was added and the incorporation of BrdU was allowed to proceed until 48 h after TSH addition, at which time all cultures were fixed, and the BrdU-labeling index was determined. The 48-h labeling index without TGFβ was 54% (normalized to 100% on the axis; ●) and the maximal inhibition by TGFβ₁ (normalized to 100% on the axis; ○) was 70% inhibition of the nuclear labeling.