Effects of serum and lipoproteins on steroidogenesis in cultured bovine luteal cells

The effects of serum and lipoproteins on the function of bovine luteal cells in tissue culture were examined. Corpora lutea from regularly cycling dairy cows were dissociated with collagenase and cultured in Ham's F-12 medium with or without serum. The serum-free medium was supplemented with insulin, transferrin and hydrocortisone. Addition of LH to the serum-containing medium did not increase progesterone (P₄) production. When the luteal cells were cultured in serum-free medium, LH produced a dose-dependent increase (P< 0.001) in P₄ production during the first 24 h of culture. The responsiveness of the cells to LH then gradually declined, and remained low until days 9-11 of culture, at which time the cells regained their ability to respond to LH. The luteal cells were responsive to dibutyryl cAMP in both serum-containing and serum-free medium. Serum lipoproteins (low and high density) were able to produce a 150-260% increase in progesterone production by the luteal cells cultured in serum-free medium. The results indicate that the presence of serum in the cell culture medium inhibits the responsiveness of luteal cells to LH at a step prior to the increase in cellular cAMP, and that serum lipoproteins can be used to increase progesterone production by cultured bovine luteal cells.