Uterine DNA synthesis and cell proliferation during early decidualization induced by oil in mice

[3H]Thymidine autoradiography was used to study cell proliferation during decidualization induced by intraluminal oil in ovariectomized mice treated with oestrogen and progesterone. Development of the decidual reaction involves two distinct populations of stromal cells. Periluminal cells start to synthesize DNA 11--15 h after instillation and by 17--20 h, without dividing, differentiate into epithelioid decidual cells which continue to incorporate [3H]thymidine, presumably becoming polyploid. Cells peripheral to this zone also start to synthesize DNA between 11 and 15 h, but at 18.5 h many have divided before differentiating. None of these dividing cells had been arrested in G2. The periluminal and peripheral cells do not appear to differ in their proliferative antecedents.