Role of lipoproteins and de-novo cholesterol synthesis in progesterone production by cultured bovine luteal cells

serum and, while dibutyryl cyclic AMP (dbcAMP) caused a marked stimulation of progesterone production in complete serum, it had only a small effect in LPDS. Lowdensity lipoprotein (LDL) and high-density lipoprotein (HDL) increased basal and dbcAMP-stimulated progesterone production. Cells were 7 times more sensitive to LDL than HDL although the maximum response to both lipoproteins did not differ significantly. Inhibition of de-novo cholesterol synthesis by compactin had no effect on dbcAMP-stimulated progesterone production by cells cultured with complete serum or LPDS plus lipoproteins. Basal progesterone production in complete serum was increased by compactin and this was associated with a marked inhibition of cell proliferation, both effects being reversed by mevalonic acid. Compactin caused a 50% reduction in dbcAMP-stimulated progesterone secretion by cells cultured in LPDS. These data show that bovine luteal cells are dependent upon lipoproteins to provide substrate for progesterone synthesis and that, while LDL is the preferred lipoprotein, both LDL and HDL may be of importance in vivo.