ROLE OF ACETYL-L-CARNITINE IN RAT-BRAIN LIPOGENESIS - IMPLICATIONS FOR POLYUNSATURATED FATTY-ACID BIOSYNTHESIS

This study was undertaken to explore the metabolic fate of acetyl-L-ca rnitine in rat brain. To measure the flux of carbon atoms into anaboli c processes occurring at regional levels, we have injected [1-C-14] ac etyl-L-carnitine into the lateral brain ventricle of conscious rats. A fter injection of [1-C-14] acetyl-L-carnitine, the majority of radioac tivity was recovered as (CO2)-C-14 expired (60% of that injected). The percentage of radioactivity recovered in brain was 1.95, 1.60, 1.30, and 0.93% at 1,3, 6, and 22 h, respectively. Radioactivity distributio n in various lipid components indicated that the fatty acid moiety of phospholipid contained the majority of radioactivity. The radioactive profile of these fatty acids showed that the acetyl moiety of acetyl-L -carnitine was incorporated into saturated (60%), monounsaturated (15% ), and polyunsaturated (25%) fatty acids [mainly present in 20:4 (5.2% ) and 22:6 (7.8%)], Injection in the brain ventricle of radioactive gl ucose, the major source of acetyl-CoA in the CNS, revealed that glucos e was a precursor of saturated (85%) and monounsaturated (15%)but not of polyunsaturated fatty acids. Thus, this study demonstrated distinct fates of glucose and acetyl-L-carnitine following intracerebroventric ular injection. In summary, these data implicate acetyl-L-carnitine as an important member of a complex acetate trafficking system in brain lipid metabolism.