Inhibition of aromatase activity impairs uterine decidualization. (A) The hormonal regimen used in the artificial decidualization protocol is shown. Mice were treated with or without letrozole (20 mg/kg body weight). Uteri were collected 72 h after the application of stimulus. (B) The extent of decidual response in ovariectomized mice treated with P (Left) and P plus letrozole (P+AI, Right) is shown. s and us denote stimulated and unstimulated uterine horns, respectively. (C) The quantitative analysis of the average weight gain of stimulated relative to unstimulated horns in mice (n = 5) subjected to artificial decidualization with or without letrozole treatment. The data are presented as mean ± SEM. (D) Uterine RNA was isolated 72 h after the initiation of decidualization and subjected to quantitative PCR analysis using gene-specific primers for ERα, alkaline phosphatase (Alkp), BMP2, connexin 43 (Cx43), and PRP. P and P+AI represent uterine RNA from ovariectomized mice treated with P and P plus letrozole, respectively.