Human low density lipoproteins (LDL) in combination with cholesterol or cholesteryl linoleate as precursors for progesterone synthesis of human placenta in organ culture.

After preincubation of term placental tissue in organ culture for 24 h, progesterone synthesis is 2-3 fold lower than without preincubation. By adding human male serum proteins (MW less than 12,400), we obtained 2-3.5 fold lower tissue levels of progesterone. Serum proteins with high molecular weight (MW greater than 12,400) are postulated to facilitate progesterone release by binding free medium progesterone. In test series without preincubation, there are no significant (p less than 0.05) differences in progesterone formation in the presence of cholesterol (C), cholesteryl linoleate (CL), and LDL. In test series with preincubation, LDL causes a twofold increase in medium progesterone with C (0.1 and 1 mM) and CL (0.1 mM) in the presence of the low molecular weight serum protein (MW less than 12,400) solution. A decrease of 50% was obtained by 1 mM CL with/and without LDL. In culture medium containing high molecular weight serum proteins (MW greater than 12,400), 0.1 and 1 mM C and CL induce a twofold increase in progesterone production without any significant (p less than 0.05) differences between the single values. No further stimulation could be observed by LDL because there was sufficient LDL for maximal progesterone formation. In conclusion, LDL enhances the utilization of cholesterol and cholesteryl linoleate for progesterone production in term placenta. A lipoprotein cholesterol receptor is suspected.