Cellular differentiation of rat uterine adenocarcinoma cells by progesterone in vitro

Transplantable cloned HTP/Cl culture was a stable line derived from a rat uterine adenocarcinoma that was induced by 7,12-dimethylbenz(a)anthracene in vivo and did not display density-dependent inhibition of growth. This HTP/Cl culture easily adapted to grow in a culture medium containing progesterone, 8 mug/ml. As compared with HTP/Cl culture, HTP/Cl/P8 culture grown in the presence of progesterone was contact inhibited, and a cellular differentiation was observed in the tumor tissues that developed after inoculation of cells. These actions of progesterone on uterine adenocarcinoma cells were completely reversible on removal of the hormone in vitro. These results appeared to indicate that progesterone was involved in the regulation of both cellular proliferation and differentiation. The possible mechanisms of the regulation of rat uterine adenocarcinoma cells by progesterone are discussed in relation to cellular levels of cyclic adenosine 3':5'-monophosphate in vitro.