Hormone regulation of growth: stimulatory and inhibitory influences of estrogens on DNA synthesis.

Estrogenic hormones first stimulate and then inhibit DNA synthesis in the uterus of the immature rat. Both the stimulatory and the inhibitory effects depend on the sustained presence of estrogen. Thus, estriol, which is equal in effectiveness to estradiol on early (up to 6 hr) responses, has only a partial stimulatory effect on DNA synthesis. Estradiol initially stimulates DNA synthesis, but the sustained presence of this steroid inhibits further synthesis of this macromolecule and cell division. These observations are discussed in terms of their relationship to current models of estrogen action and to estrogen dependency in some types of cancer.