We examined the dose response, time course and reversibility of the effect of methyl 2-tetradecylglycidate (McN-3716, methyl palmoxirate or MEP), an inhibitor of β-oxidation of fatty acids, on incorporation of radiolabeled palmitic acid (U-14CPA) from plasma into brain lipids of awake rats. MEP (0.1, 1 and 10 mg/kg) or vehicle was administered intravenously from 10 min to 72 hr prior to infusion of U-14CPA. Two hr pretreatment with MEP (0.1 to 10 mg/kg) increased brain organic radioactivity 1.2 to 1.8 fold and decreased brain aqueous radioactivity by 1.2 to 3.0 fold when compared to control values. At 10 mg/kg, MEP significantly increased brain organic fraction from 40 in controls to 85, 30 min to 6 hr pretreatment, and resulted in a redistribution of the radiolabeled fatty acid toward triacylglycerol. MEP changed the lipid/aqueous brain ratio of incorporated U-14CPA from 0.67 to 5.7. The incorporation rate coefficient, k*, was significantly increased by MEP (10 mg/kg) at 2 hr (31), 4 hr (59) and 6 hr (34). All effects were reversed by 72 hr, consistent with a half-life of ∼2 days for carnitine palmitoyl transferase I. These results indicate that intravenous MEP may be used with 1-11Cpalmitic acid for studying brain lipid metabolism in vivo by positron emission tomography, as it significantly reduces the large unincorporated aqueous fraction that would result in high background radioactivi
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