Washizaki K, Smith Q R, Rapoport S I, Purdon A D
Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892.
J Neurochem. 1994 Aug;63(2):727-36. doi: 10.1046/j.1471-4159.1994.63020727.x.
Brain fatty acid incorporation into phospholipids can be measured in vivo following intravenous injection of fatty acid tracer. However, to calculate a cerebral incorporation rate, knowledge is required of tracer specific activity in the final brain precursor pool. To determine this for one tracer, unesterified [3H]arachidonate was infused intravenously in pentobarbital-anesthetized rats to maintain constant plasma specific activity for 1-10 min. At the end of infusion, animals were killed by microwave irradiation and analyzed for tracer specific activity and concentration in brain phospholipid, neutral lipid, and lipid precursor, i.e., unesterified arachidonate and arachidonoyl-CoA, pools. Tracer specific activity in brain unesterified arachidonate and arachidonoyl-CoA rose quickly (t1/2 < 1 min) to steady-state values that averaged < 5% of plasma specific activity. Incorporation was rapid, as > 85% of brain tracer was present in phospholipids at 1 min of infusion. The results demonstrate that unesterified arachidonate is rapidly taken up and incorporated in brain but that brain phospholipid precursor pools fail to equilibrate with plasma in short experiments. Low brain precursor specific activity may result from (a) dilution of label with unlabeled arachidonate from alternate sources or (b) precursor pool compartmentalization. The results suggest that arachidonate turnover in brain phospholipids is more rapid than previously assumed.
静脉注射脂肪酸示踪剂后，可在体内测量大脑脂肪酸掺入磷脂的情况。然而，要计算大脑掺入率，需要了解最终大脑前体池中的示踪剂比活。为了确定一种示踪剂的这一参数，将未酯化的[3H]花生四烯酸静脉注入戊巴比妥麻醉的大鼠体内，以在1 - 10分钟内维持血浆比活恒定。输注结束时，通过微波辐射处死动物，并分析大脑磷脂、中性脂质和脂质前体（即未酯化花生四烯酸和花生四烯酰辅酶A池）中的示踪剂比活和浓度。大脑未酯化花生四烯酸和花生四烯酰辅酶A中的示踪剂比活迅速上升（t1/2 < 1分钟）至稳态值，平均为血浆比活的< 5%。掺入迅速，因为在输注1分钟时，> 85%的大脑示踪剂存在于磷脂中。结果表明，未酯化花生四烯酸迅速被大脑摄取并掺入，但在短期实验中，大脑磷脂前体池未能与血浆达到平衡。大脑前体比活低可能是由于（a）来自其他来源的未标记花生四烯酸对标记物的稀释，或（b）前体池的分隔。结果表明，大脑磷脂中花生四烯酸的周转比以前认为的更快。
