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Organochlorines are lipophylic molecules that accumulate in the fat where they remain for years. During weight loss, they are mobilized and their concentration increases in blood. The present work tests, in transgenic estrogen-reporter mice (ERE-tK-LUC), whether this increase is sufficient to modulate the estrogen receptors (ERs) in the whole body. Three weak estrogens were studied: p,p′DDT [1,1,1-trichloro2,2-bis(p-chlorophenyl) ethane], p,p′DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene], and βBHC [β-benzene-hexachloride].Dose-dependent analysis of reporter expression (luciferase) were performed in tissues of acutely treated mice. A body map of ER activation was obtained. All these chemicals modulated the reporter, although with a different efficiency and depending upon the tissue analyzed. Induction was confirmed in the liver by determining the expression of the endogenous progesterone receptor (PR) gene, at the dose and time point at which the luciferase gene was maximally induced.After experimental accumulation in the fat tissue, followed by a 48-h period of fasting, we tested whether these compounds could be mobilized to reach sufficient levels to activate the ERs in selected reproductive and nonreproductive tissues (testicle, prostate, liver, and lung). This experimental setting produced results that were different than those obtained following acute treatments. In loaded mice, fasting induced βBHC mobilization resulted in strong ER activation in the liver and the lung, which was blocked by ICI-182780. p,p′DDT mobilization had no effect in these tissues, but it acted efficiently in the prostate and testis. βBHC inhibited the ERE-mediated reporter in the testicle and induced the reporter in the prostate. In this tissue, βBHC action was not inhibited by the anti-estrogen ICI-182780. During fasting, βBHC, p,p′DDT, and metabolite p,p′DDE increased in blood concentration, from 2.25 ± 0.25, 0.51 ± 0.09, and 0.38 ± 0.06 μg/ml to 8.24 ± 0.95, 4.52 ± 0.68, and 5.06 ± 0.57 μg/ml, respectively. The effect produced by these organochlorines in the liver correlates with the modulation of the ERα protein.We conclude that these organochlorines modulate differently the expression of estrogen-regulated genes in male mice. Their effect is tissue- and compound-specific and is dependent on the energetic balance.