Acta Pharmacologica Sinica 2005 February; 26 (2): 212-219; doi: 10.1111/j.1745-7254.2005.00536.x

Aim: To investigate the effect of mifepristone (RU486) as a single dose on pinopodes expression in the endometrial surface of mice at the time of implantation.

Methods:  Pregnant mice in the treated four groups received mifepristone subcutaneously (0.1 mg) between 07:00 and 08:00 AM on Pd (day of pregnancy)1, Pd2, Pd3, and Pd4. Pregnant mice in the non-treated group were used as controls. The uterine horns were collected randomly from two mice in each group between 21:30 and 22:00 PM on Pd4, and from another two mice of the same group between 09:30 and 10:00 AM on Pd5. The specimens were examined by scanning electron microscopy for the detection of pinopodes.

Results: When mifepristone was given on Pd1, developing and fully developed pinopodes were observed, but the expression was markedly reduced compared to the control group. When mifepristone was administered on Pd2, only a few developing pinopodes were present. When mifepristone was administered on Pd3, developing pinopodes were observed. When mifepristone was administered on Pd4, different development stage pinopodes were present in specimens collected between 21:30 and 22:00 PM on Pd4, but no pinopodes was observed in specimens taken between 09:30 and 10:00 AM on Pd5.

Conclusion: These findings suggest that administration of a single dose of RU486 subcutaneously on Pd1, Pd2, Pd3, and Pd4 might play a role in inhibiting development and maturation of endometrium, hence affecting embryo implantation in mice.

Keywords: mifepristone; endometrium; pinopode; embryo implantation; contraception