In the present study, resorption/abortion was induced between days 25 and 45 of gestation with aglepristone (group IRA, n =10). The aim was to observe the change in the distribution of progesterone (PR) and estrogen receptors (ER), in receptors (ER), in comparison to a group of spontaneous resorptions/abortions (group SRA, n=5), and further group of normal healthy pregnant animals, ovariohysterectomized between days 25 and 45 of gestation (controls, n = 7). The receptors were assessed by means of immunohistochemistry (1HC) and RT-PCR. at the placental and interplacental sites of the uterine horn as well as in the corpus uteri. Significant differences were observed between the controls on one side and the groups of resorption/abortion on the other side. The total scores of the progesterone receptors (TPR) in the placental and interplacental part of the uterine horn, was significantly lower in the endometrial stromal cells (ESC) of the control group than in those of the SRA- and IRA-group, respectively (placenta: 5.8 vs. 6.5 and 6.7, p < 0.01: interplacental sites: 5.6 vs. 6.6, p < 0.05). In contrary, the total scores of the estrogen receptors (TER) at interplacental sites and the corpus uteri, respectively, was significantly higher in the myometrial smooth muscle cells (MSMC) and the ESC (p < 0.05) of the controls. We therefore conclude, that the here observed differences between groups point to an upregulation of TPR- and a down-regulation of TER-scores in endometrial stromal cells at different uterine sites during resorption/abortion, which indicates a special role of these cells. (c) 2008 Published by Elsevier Inc.