Figure 1.

Contrasting effects of thyroid hormone on tadpole intestinal epithelial and fibroblastic cells. The fibroblasts (A) and epithelial cells (B) were isolated from stage 57/58 of tadpole small intestine and then cultured on a six-well plastic dish in 60% L-15 medium containing 10% T₃- depleted fetal bovine serum at 25°C in the presence or absence of 10 or 100 nM T₃. The live cells were counted daily by trypan blue staining. Note that the epithelial cell number decreased even when no exogenous T₃ was present. This could be because of the residual T₃ in the treated serum. DNA fragmentation and flow cytometry analyses (Figs. 2 and 3) indicated that at least part of this decrease was due to apoptosis.