Effect of chronic stress on estradiol action in the uterus of ovariectomized rats.

The aim of this study was to investigate the development of estradiol (E2) effects in ovariectomized rat uterus under chronic stress. The chronically stressed rats (swimming and overcrowded cages) were treated with a single injection of E2 dipropionate (10 micrograms/ rat, i.m.) in olive oil (0.1 ml/rat). Control groups of ovariectomized rats included one group treated with the same dose of E2 but maintained in stress-free conditions, a second group subjected to the same procedure of chronic stress but injected with olive oil only, a third group treated with olive oil and maintained in stress-free conditions, and a final group which consisted of uninfluenced ovariectomized rats. E2 effects were determined by measuring activity of proliferation (mitotic index), cellular, nuclear, and nucleolar volumes (morphometry), DNA content (Feulgen's method) in luminal and glandular epithelia, stromal cells of endometrium at 24, 36 and 48 h after injection of E2 or olive oil. In chronically stressed rats treated with E2, at each time point almost all the parameters in all the structures were significantly (P < 0.05-0.001) higher, than in unstressed E2-treated rats. In E2-untreated rats, the stress did not influence uterine tissues. Thus, the chronic stress enhances strongly the E2-induced effects in the uterus of ovariectomized rats. It is likely mediated by the changes of some steps in the mechanism of estrogen action that leads to the increase in the sensitivity of uterine structures to estrogens.