High density lipoprotein utilization by dispersed rat luteal cells.

Utilization of lipoproteins by cells prepared by collagenase dispersion of ovaries of immature gonadotropin-primed rats was studied. Human and rat HDL increased basal progestin secretion and incorporation of [14C]oleate into cellular sterol esters 2-fold during a 2 h incubation, with maximal stimulation occurring at a lipoprotein sterol concentration of 125 micrograms/ml. This concentration of HDL cholesterol also increased progestin production by cells stimulated with dibutyryl cyclic AMP. Human LDL or cholesterol-rich lipid dispersions had little effect upon either progestin secretion or sterol esterification at similar sterol concentrations. However, addition of delipidated human HDL apolipoproteins to the cholesterol-rich lipid dispersions markedly enhanced progestin production. Incubation of the dispersed cells in the presence of 25 micro M ML-236B, which blocked cellular de novo sterol synthesis by over 90%, had no effect upon progestin secretion. Specific uptake of human 125I-labeled HDL by the dispersed cells was observed. Analysis fo 125I-labeled HDL uptake as a function of lipoprotein concentration indicated that the uptake process was saturated at HDL levels of 200-400 micrograms protein/ml. The amount of HDL specifically associated with the cells at saturating levels after 1 h of incubation was sufficient to account for the increased progestin synthesis and sterol ester storage observed during this time. During the incubations cell-specific degradation of the 125I-labeled HDL apolipoprotein appeared to be minimal. We conclude that lipoprotein-carried cholesterol is an important substrate for rat luteal cells and that these cells possess a specific mechanism for the uptake of HDL.