| Objectives: To explore if there is chemopreventive effects of estrogen on 1,2-dimethylhydrazime induced aberrant crypt foci formation in rats .Methods: Thirty six 4-months-old female Sprague-Dawleye rats were underwent ovariectomy, then were randomly divided into 3 groups (A, B, C, n=12). In Group A the positive control, rats were treated weekly with DMH (25mg/kg, intraperitoneal injection) and experimental sesame oil (0.1ml/100g, subcutaneous injection) for 8 weeks. In Group B rats were treated weekly with DMH and estradiol cypionate (dissovled in sesame oil, 250μg/kg, subcutaneous injection, 10weeks). In Group C the negative control, rats were treated with same volume normal saline and experimental sesame oil. (All rats were bred in standard clean condition). After12 weeks treatment, all the rats were sacreficed and the colon were collected for ACF counting, and the expression of ER-βmRNA, PCNA,β-catenin, and caspase-9 protein were evaluated.Results: The average numbers of ACF, AC(1-3), AC(4-6), AC(>6) were 57.40±4.88,31.20±5.81, 17.60±1.14, 8.60±1.14 respectively in group A, and 36.60±4.09,22.00±3.46, 10.40±1.67, 4.20±1.09 respectively in group B, there was significant difference in two groups(p<0.001),and there was no ACF formation in group C. The expression level of ER-β mRNA in rat colon epithelium in group B was higher than that in group A (p<0.001) and group C (p=0.04). The PCNA labeling index andβ-catenin labeling index of rat colon epithelium in group B were lower than that in group A respectively (p<0.001, p<0.001). The expression level of protein caspase-9 of rat colon epithelium in group B was higher than that in group A (p<0.001).Conclusion: The estrogen reduced the formation of aberrant crypt foci via inhibiting proliferation and inducing apoptosis in rat colon epithelium.
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