DEVELOPMENT OF A CULTURE SYSTEM FOR BOVINE LUTEAL CELLS: EXAMINATION OF LUTEOTROPIC AND LUTEOLYTIC MECHANISMS
The function of bovine luteal cells in tissue culture was 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 P(,4) production. When the luteal cells were cultured in serum-free medium, LH produced an increase in P(,4) during the first 24 hours of culture. The responsiveness of the cells to LH then declined, and remained low until approximately day 7 of culture, at which time the cells regained their ability to respond to LH. The luteal cells were responsive to dbcAMP in both serum-containing and serum-free medium. These 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. The addition of either low density or high density lipoprotein to the serum-free cultures produced a 150-260% increase in P(,4) production without inhibiting the LH response. In the presence of lipoproteins, ('14)C-acetate incorporation into sterols and steroids was greatly decreased. These experiments suggest that cultured bovine luteal cells can use serum lipoproteins as a source of cholesterol to increase P(,4) synthesis, and the lipoproteins can influence endogenous cholesterol metabolism. The long-term effects of PGF(,2(alpha)) on luteal function were examined using this cell culture system. PGF(,2(alpha)) has either no effect on basal P(,4) production, or is slightly stimulatory. During the first 24 hours of culture, PGF(,2(alpha)) has no effect on LH-, cholera toxin-, or forskolin-stimulated P(,4). However, after day 1, PGF(,2(alpha)) inhibits the agonist-induced increases in P(,4), resulting in levels of P(,4) that are not different from controls. PGF(,2(alpha)) is also capable of blocking indomethacin-stimulated increases in P(,4) production. These findings indicate that although PGF(,2(alpha)) does not decrease basal steroidogenesis, it is able to block agonist-induced increases in P(,4) after day 1. The site of action of PGF(,2(alpha)) is beyond the LH receptor, and is either at, or beyond, the adenylate cyclase molecule.
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