Action of 17α- and 17β-E2 on uterine mass in adult ovariectomized rats. 17α-E2 significantly increased the uterine weight as compared with the vehicle (corn oil; *P < 0.05), although this increment was significantly less than those of 17β-E2 (+P < 0.00005). In rats treated with 17β-E2 plus different doses of 17α-E2, less uterotrophic effect of 17β-E2 was evident. Statistical significance: **P < 0.005, ***P < 0.0005, ****P < 0.0001. The analysis shows that the treatment 1:1 (a) was different from 1:3, 1:5 and 1:100 (b; P < 0.05), which were not different between them (b; P > 0.05). Each bar represents the mean ± SEM, n = 6 rats per group.