It is suggested that the action of peroxisome proliferator-activated receptors (PPARs) cross-talks with estrogen signaling in the uterus. However, it is not known how PPAR agonists affect estrogen-dependent processes in the uterus, especially proliferation and morphogenetic changes. The effects of agonists of PPAR-alpha and -gamma on proliferative and morphogenetic reactions in the uterus under short- and long-term estrogen treatments were therefore examined. Ovariectomized mice were treated with estradiol dipropionate (4 micro g/100 g, s.c., once a week) or vehicle and rosiglitazone (PPAR-gamma agonist) or fenofibrate (PPAR-alpha agonist) or with no additional treatment for 2 days or for 30 days. Treatment with estradiol and PPAR agonists for 2 days did not affect uterine mass. In mice treated with estradiol and rosiglitazone for 2 days, proliferation was enhanced and levels of estrogen receptors-alpha and beta-catenin were decreased in all uterine tissues. Treatment with estradiol and fenofibrate for 2 days had the opposite effects on the parameters tested. In animals treated with estradiol and rosiglitazone for 30 days, uterine mass was increased, abnormal uterine glands and atypical endometrial hyperplasia were found more often and levels of estrogen receptors-alpha and beta-catenin were decreased. In animals treated with estradiol and fenofibrate for 30 days, uterine mass was decreased, most of the uterine glands had a normal structure, no cases of atypical hyperplasia were diagnosed, proliferative activity was declined and the levels of estrogen receptors-alpha and beta-catenin were markedly higher. Treatment with rosiglitazone or fenofibrate did not affect the serum estradiol level in the mice which received estradiol together with PPAR agonists for 30 days. Thus, rosiglitazone exerted the proliferative and morphogenetic effects of estradiol, but fenofibrate had the opposite effect. The actions of rosiglitazone and fenofibrate are associated with changes in the expression of estrogen receptors-alpha and beta-catenin in the uterus.

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