The members of the collaboration are provided in Appendix A.

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The effects on [14C] sterol synthesis and excretion by exposure of L‐929 cells to several phosphatidylcholines (PC) has been examined. No significant effects were noted on either parameter during a 6‐hr period if exposure of cells to the phospholipid preceded the addition of [1‐14C] acetate by just 30 min. However, if cultures were grown in media containing delipidized serum and 2×10−5 M PC through 2 or more subculturings prior to adding [1‐14C] acetate, the amount of [14C] sterol increased in both cells and medium by 70–200% when saturated or monounsaturated PC were used. Dilinoleylphosphatidylcholine (18∶2 PC) at the same concentration did not stimulate synthesis or excretion of newly synthesized sterol. Total cellular sterol was determined by gas chromatography, and was only marginally affected by long‐term exposure to dipalmitylphosphatidylcholine (16∶0 PC), whereas the total sterol of the medium increased by 4‐fold over a 19‐hr period. Cultures which had been exposed to 16∶0 PC through 3 subculturings continued to display enhanced de novo sterol synthesis, but not excretion, for up to 5 hr after replacement with fresh medium lacking 16∶0 PC. The disparity in response to 2×10−5 M levels of 16∶0 PC and 18∶2 PC may relate to differences in metabolism of cellular fatty acids, whereas relatively small changes in the cellular fatty acid composition were noted with 16∶0 PC‐treated cells. The results indicate that extracellular PC can promote sterol synthesis and excretion by L‐929 cells, and that the magnitude of this response is influenced by the time of exposure to the phospholipid and by its fatty acid composition.