In vivo labeling of brain phospholipids by long‐chain fatty acids: Relation to turnover and function

An experimental method and model are described to quantitate kinetics of in vivo incorporation of fatty acids (FA) into stable brain phospholipids. When a radiolabeled long‐chain FA is injected intravenously in a rat, it rapidly equilibrates with brain FA‐CoA, the precursor pool for phospholipids. As different labeled FA enter different sn positions of specific phospholipids, a combination of labels can be used to investigate roles of different phospholipids in brain function and structure. By taking into account dilution λ of specific activity of brain FA‐CoA, compared with specific activity of FA in plasma, half‐lives of FA in individual brain phospholipids can be calculated. Values for λ less than 0.02 suggest marked recycling, and give half‐lives two orders of magnitude smaller than literature values. A half‐life of arachidonate in phosphatidyli‐nositol of 0.66 h (turnover=105%h) is consistent with active participation of this FA in phospholipase A 2 mediated signal transduction.