Characteristic expression of cholesterol sulfate in rabbit endometrium during the implantation period

Sialic acids and sulfate residues are the major negative-charged cellular components, which are considered to be crucial in embryonal adhesion to the endometrium. To explore the mechanism of implantation, we examined the change in the amounts of these substances in the rabbit endometrium during the implantation period. Gangliosides and sulfatides were present in very small quantity in the endometrium irrespective of the reproductive stage. Though the content of cholesterol sulfate was relatively low in the nonpregnant endometrium, it abruptly increased at day 5 of pregnancy, i.e. at the beginning of implantation, followed by a gradual decline toward day 9. Cholesterol sulfate level in the inter-implantation sites was about twice as much as that in the implantation sites and was comparable with that in the pseudopregnant endometrium. These results demonstrate that cholesterol sulfate is a major negative-charged lipid in the peri-implantation endometrium in rabbits. We further point to the difference in the concentration of cholesterol sulfate between implantation and interimplantation sites, thus suggesting cholesterol sulfate as a major participant in the process of implantation.