Abstract: This study was designed to explore the effects of Letrozole which is an P450 aromatase inhibitor on ovarian development in mice. SPF degree of Kunming female mice were randomly divided into control and 2,4,6,8,10,30,50 g/kg of Letrozole dose groups, consecutive administration for 3 d. At the 9, 15 and 30 d after stopping administration, the ovarian development was detected. The results showed that： ①The ovary index was significantly （P<0.05） increased in 6 and 8 g/kg groups at the 9 and 30 d，and 4 to 10 g/kg groups at the 15 d compared with control group, however, it was significantly （P<0.05）decreased in 50 g/kg groups at the 9 and 30 d compared with control group and 2,4,6,8,10 g/kg groups; ②The number of primary follicle was significantly（P<0.05）increased in 4,6,8 g/kg group at the 9 and 15 d and 6 g/kg group at the 30 d compared with control group and other dose groups, however, it was significantly（P<0.05）decreased in 30 and 50 g/kg groups at the 9 d and 50 g/kg group at the 15 d and 10,30,50 g/kg group at the 30 d compared with control group and other dose groups; ③The number of secondary follicle was significantly （P<0.05） increased in 4,6,8 g/kg groups at the 9,
15 and 30 d, however, it was significantly （P<0.05） decreased in 30 and 50 g/kg groups at the 9 d compared with control group; ④The number of mature follicle was significantly（P<0.05）increased in 4,6,8 g/kg groups at the 9 d and 6 and 8 g/kg groups at the 15 d and 2,4,6,8 g/kg groups at the 30 d, however, it was significantly （P<0.05） decreased in 10 to 50 g/kg groups at the 9 d and 30 and 50 g/kg groups at the 15 and 30 d compared with control group. These results indicated that the concentration of Letrozole with 4,6,8 g/kg can inhibited the P450 aromatase activity to some extent, reducing endogenous estrogen synthesis and promote the development of ovaries and follicles in mice.

Key words: mice; ovary; P450 aromatase; Letrozole