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 lambda 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 lambda 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 phosphatidylinositol of 0.66 h (turnover = 105%h) is consistent with active participation of this FA in phospholipase A2 mediated signal transduction.