Relative mitogenic activities of various estrogens and antiestrogens.

The abilities of a variety of estrogens and antiestrogens to stimulate DNA synthesis in the prepuberal rat uterus were compared. One microgram of each compound was administered in vivo via a single intraperitoneal injection. DNA synthesis was assayed in vitro in isolated nuclei 24 h later. The relative mitogenicities of the steroidal estrogens were: 16 alpha-E2 less than 17 alpha-E2 = E3 = 16-EpiE3 less than 16 beta-E2 = 17 beta-E2. The potencies of several nonsteroidal estrogens were also tested. Indenestrol A was as potent at 17 beta-E2, whereas indanestrol and dimethylstilbestrol had weaker activities. The antiestrogens, nafoxidine and 4-hydroxytamoxifen, were both potent stimulators of DNA synthesis. The abilities of an estrogen to stimulate increases in uterine wet weight, DNA polymerase alpha activities, and DNA synthesis in uterine nuclei 24 h after injection were closely correlated. Because the magnitude of the stimulation of DNA synthesis was greatest, its measurement is the most sensitive of these assays of uterotrophic activity.