Abstract: Objective To investigate the role of GATA-4 in the pathogenesis of polycystic ovary syndrome (PCOS), and to provide some experimental data for the application of the rat model induced by letrozole. Methods Forty female rats were randomly divided into two groups, PCOS model group and control group. The rats in model group were administered letrozole with the dosage of 1mg/(kgI>&#/I>8226;d) dissolved in 10g/L carboxymethyl cellulose（CMC） by P.O./Q.D. for 21 days, and rats in the control group were administered with equal dosage and volume of CMC by P.O/Q.D. for 21 days. Gonadal hormone concentrations in serum were determined by radioimmunoassay; the histological changes in ovarian tissues were observed with HE staining, and the expression of GATA-4 in ovary tissue was detected by immunohistochemistry, real\|time PCR and Western blotting. Results With the comparison of two groups, the concentrations of estradiol and progesterone were found considerably reduced in the control group （EM>P/EM><0.05）, while the serum testosterone, follicle\|stimulating hormone(FSH) and luteinizing hormone(LH) levels were found increased markedly in the model group （EM>P/EM><0.05）. The ovaries in the model group showed high incidence of subcapsular ovarian cyst and capsular thickening and decreased number of corpora lutea comparing to those in the control group. The expression of GATA-4 in preantral follicle and antral follicle granulosa cells in the model group was significantly higher than those in the control group.With the observation on and comparison of staining densities, the mRNA transcription and protein depression of GATA-4 were significantly stronger in the model group than those in the control group（EM>P/EM><0.05）. Conclusion The extra higher expression of GATA-4 in follicle granulosa cells may be significantly correlated with the pathophysiology mechanism of PCOS. The

Key words: Polycystic ovarian syndrome, GATA-4, Letrozole, Ovary, Immunohistochemistry, Real\|time PCR, Western blotting, Rat