| Abstract: | Receptor-mediated uptake of low density lipoprotein (LDL) has been shown to provide a major source of cholesterol for a variety of cell types, particularly steroidogenic cells. In this study, the functional significance of lipoproteins in porcine ovarian granulosa cells and their mechanism of uptake by the cell was examined. Porcine LDL and high density lipoprotein (HDL) were isolated using a KBr density gradient, and the purity of both lipoproteins was confirmed by single corresponding bands on agarose gel stained for lipid and protein. Purified LDL and HDL were radioiodinated and labelled with colloidal gold for binding and tracer studies respectively. Both lipoproteins bind to cell surface and are internalized within 30 min at 37 degrees C. The cultured granulosa cells possess more HDL binding sites than LDL binding sites and are more responsive in progesterone production when supplemented with HDL. These results suggest that granulosa cells may preferentially utilize HDL over LDL as a source of cholesterol for steroidogenesis. |
