Cell density influences hormonal responsiveness but not lipoprotein utilization in cultured bovine luteal cells

The objective of the present study was to investigate the effect of cell density on hormonal responsiveness and lipoprotein utilization by cultured bovine luteal cells. Luteal cells obtained from regularly cycling dairy cows were plated at three culture densities: 0.5 × 10⁶, 1 × 10⁶ and 2 × 10⁶ cells/flask in serum-free Ham's F-12 culture medium, and maintained for 9 days. Basal steroidogenesis was unaffected by cell density, while LH responsiveness was greatest in low density cultures. Progesterone produced in response to LH (10 ng/ml) was greater than control levels throughout the culture period in low density cultures. Luteal cells cultured at medium and high densities became responsive to LH only later in the culture period (days 5 and 9, respectively). In contrast, prostaglandin F_2α (PGF_2α, 100 ng/ml) was more effective in high density cultures, causing a complete inhibition of LH stimulation and returning progesterone levels to basal values. In low density cultures, treatment with PGF_2α + LH resulted in progesterone levels that were not significantly different from LH-treated cultures. There was no effect of cell density on utilization of either low density lipoprotein (LDL) or high density lipoprotein (HDL) for steroidogenesis. However, a synergistic effect of LH with either lipoprotein was observed in low and medium density, but not high density cultures. From these results, it is concluded that culture density can influence the responsiveness of bovine luteal cells to either LH or PGF_2α, but has no effect on lipoprotein utilization by these cells.