Effects of conceptus derived substances on the angiogenesis in the corpus luteum of pregnant rats

Effects of conceptus-derived substances on the angiogenesis of the corpus luteum (CL) were examined in pregnant rats. Labeling index (LI), the ratio of endothelial cells which labeled with bromodeoxyuridine, was used to evaluate angiogenesis. In pregnant rats with 10 or more conceptuses (Fc group), LI increased rapidly from day 12 to day 14 of pregnancy, whereas in the rats whose sonseptus number was reduced to one on day 7 (D7asp group) or day 12 (D12asp group) of oregnancy, there was no increase in LI on day 14 of pregnancy. Subcutaneous implantation of testosterone capsules, a major placental hormone which is converted to estrogen in the CL, between day 12 and 14 of pregnancy increased LI values only in the D12asp group but not in the D7asp group. The nuclear contant of estrogen receptor, which was determined by the EIA using a specific monoclonal antibody, was also increased by testosterone treatment in the D12asp group, but not in the D7aso group. These results indicated that the conceptus-derived substances wuold stimulate the ability of the CL respond to estrogen between day 7 and day 12 of pregnancy, which would be essential for the CL to develop its angiogenesis after day 12 of pregnancy.