Abstract: The ability of steroid hormones to modulate endometrial differentiation has been studied in guinea pigs. The purpose of the study was to determine the hormonal conditions favorable for supporting decidual I tissue formation and effects of progestin，antigestagen，estrogen and antiestrogen on uterine cell differentiation. The results indicated that the induction and extent of decidual formation were dependent on the progestin and estrogen. Estrogen is essential for supporting the progestin directed differentiation and proliferation of endometrium with the formation of decidual tissue in stimulated guinea pigs. The ability of decidual-ization occuring in the guinea pig only requires the endometrium be initially primed by these ovarian steroid hormones. The results also demonstrated that antigestagen RU486 and antiestrogen Clomiphene influence endometrium differentiation and decidual tissue formation.

Key words: "Guinea pig, Decidua, Progestin, Estrogen, RU486, Clomiphene "