Effect of estrogen on cell proliferation in colonic mucosa of the mouse

The effect of estrogen on cell proliferation in the descending colon of the mouse as an example of a non-target organ was investigated. Ovariectomized mice were given single or multiple injections of 10 ng/g body weight of 17β-estradiol and were killed 1 h after³H-thymidine injection. Estrogen treatments decreased incorporation of³H-thymidine into the DNA of colonic mucosa most markedly at 4 h after the single or the last of multiple injections. The inhibitory effect of estrogen on³H-thymidine incorporation was greater and lasted longer after a single injection than after multiple ones. A similar inhibitory effect was observed in the colonie mucosa of male mice as well as in the mucosa of mice in which colonie epithelial cell proliferation was enhanced by refeeding after 48 h of fasting. However, the colonie mucosa of mice treated with estrogen implants for up to 4 days was not affected. Estrogen treatments caused no significant change in the DNA, RNA and protein contents of the colonie mucosa. The efficacy of estrogen treatments was verified by an increase in both the wet and dry weights of the uterine horns of ovariectomized mice.