Localization of 3H-estradiol in the uterus of pregnant and non-pregnant armadillos

Summary The uptake and retention of radiolabeled estradiol by the uterus was examined in the armadillo. One pregnant and two non-pregnant armadillos were treated with 1.4 g/kg body weight of ³H-estradiol (E₂) by injection into the left ventricle, and one non-pregnant animal was injected with both the labeled hormone and 140 g/kg body weight of unlabeled E₂. One and a half hour after injection, the animals were sacrificed and the uteri were removed and processed for autoradiography. In the non-pregnant animals, nuclear localization was observed in the interstitial cells and glandular epithelium of the endometrium and the connective tissue cells and smooth muscle of the myometrium. Additionally, there was a gradation of uptake in the epithelial cells of the endometrium in that the glandular cells of the basal region were heavily labeled, while those cells in the sinusoidal, and luminal regions contained successively less label. The luminal cells were poorly labeled. In the pregnant female, the smooth muscle and glandular cells hypertrophied and their nuclei contained less label than was observed in the non-pregnant animals. The arteries of the myometrium were more easily distinguished in the pregnant animals and the nuclei of the endothelial cells and smooth muscle were more consistently labeled than those of the non-pregnant armadillos.