Influence of human lipoproteins on the progesterone synthesis of human term placenta in organ culture.

In the presence of LDL (200 micrograms/ml) and HDL (400 micrograms/ml), the uptake of radioactive cholesterol by a human term placenta in organ culture was enhanced by about 1.5 and 2.5, respectively, after 24-h incubation. Using cholesterol linoleate, the ratio was 1.0 and 1.5, and the tissue concentration of progesterone was 5-fold higher in the presence of LDL (600 micrograms/ml) than in the presence of HDL (4.4 mg/ml). A dose-dependent increase in medium progesterone was found using either LDL or HDL in combination with cholesterol or cholesterol linoleate, respectively. In human term placenta in organ culture, the human lipoproteins LDL and HDL both have a carrier function for cholesterol and cholesteryl linoleate, stimulate the uptake of these steroids in the placental tissue, and enhance placental progesterone formation. Furthermore, the lipoproteins facilitate progesterone release from the placental tissue.