Green P, Yavin E
Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel.
J Lipid Res. 1993 Dec;34(12):2099-107.
Tracer amounts of either [1-14C]linolenic (18:3n-3, LNA), or [1-14C]linoleic (18:2n-6, LA) acids were intracranially injected into 19- to 20-day-old rat fetuses, and the time course of the in vivo formation and esterification of their long chain polyenoic metabolites was determined for up to 20 h. A rapid disappearance of free LNA and LA, with apparent half-lives of 60 and 40 min, respectively, was noticed. One hour after LNA injection, 32.3% and 14.3% of the total brain radioactivity was found in the neutral glyceride (NG) and phospholipid (PL) fractions, respectively. After 20 h, PL radioactivity attained a level of 75%. Phosphatidylcholine (PC), diacylglycerol (DG), and triacylglycerol (TG) constituted 40%, 23%, and 9% of the total brain label at 1 h, and 35%, 10% and 14% at 20 h, respectively. Ethanolamine-containing PL (including plasmalogen) radioactivity accounted for about 10% up to 6 h and increased nearly 3-fold at 20 h, primarily due to an increase in the amount of labeled docosapentaenoic and docosahexaenoic acids (DHA), the elongation-desaturation products of LNA. A similar pattern of incorporation into NG and PL fraction was observed after the administration of [1-14C]LA. After 1 h, PC, DG, and TG species constituted 23%, 10%, and 23% of the total brain radioactivity, whereas after 20 h it accounted for 44%, 6%, and 10%, respectively. Although radioactivity in the ethanolamine PL also increased substantially from 4% at 1 h to 29% at 20 h, the main labeled fatty acid in this fraction was LA. Labeled arachidonic acid (AA) constituted 42.7% of the total radioactivity in phosphatidylinositol (PI) at 20 h. At this time, it comprised 12.5% and 14% of the total radioactivity in PC and ethanolamine PL, respectively, suggesting a high degree of esterification selectivity. Comparison of the total amounts of LA and LNA and their corresponding labeled AA and DHA metabolites in brain and liver after 3 and 6 h indicated that the contribution of liver metabolism to the elongation-desaturation under these conditions was negligible. One hour after intracerebral injection of [3H]DHA (22:6n-3) or [3H]AA (20:4n-6), 29.2% and 12% of total radioactivity, respectively, was found in the ethanolamine PL while 20% and 40% was incorporated in PC, respectively. PI labeling by [3H]AA was 6- to 8-fold higher than that seen in the presence of DHA. A high percent of radioactivity (26.9% and 18.2%) was found in DG and TG species.(ABSTRACT TRUNCATED AT 400 WORDS)
将微量的[1-¹⁴C]亚麻酸（18:3n-3，LNA）或[1-¹⁴C]亚油酸（18:2n-6，LA）颅内注射到19至20日龄的大鼠胎儿体内，并测定其长链多烯代谢产物在体内形成和酯化的时间进程，最长达20小时。观察到游离LNA和LA迅速消失，其表观半衰期分别为60分钟和40分钟。注射LNA 1小时后，中性甘油酯（NG）和磷脂（PL）组分中分别有32.3%和14.3%的全脑放射性。20小时后，PL放射性达到75%的水平。磷脂酰胆碱（PC）、二酰甘油（DG）和三酰甘油（TG）在1小时时分别占全脑标记物的40%、23%和9%，在20小时时分别占35%、10%和14%。含乙醇胺的PL（包括缩醛磷脂）放射性在6小时内约占10%，在20小时时增加近3倍，这主要是由于标记的二十二碳五烯酸和二十二碳六烯酸（DHA）的量增加，它们是LNA的延长-去饱和产物。给予[1-¹⁴C]LA后，观察到其掺入NG和PL组分的模式相似。1小时后，PC、DG和TG组分分别占全脑放射性的23%、10%和23%，而20小时后分别占44%、6%和10%。虽然乙醇胺PL中的放射性也从1小时时的4%大幅增加到20小时时的29%，但该组分中的主要标记脂肪酸是LA。在20小时时，标记的花生四烯酸（AA）占磷脂酰肌醇（PI）中总放射性的42.7%。此时，它分别占PC和乙醇胺PL中总放射性的12.5%和14%，表明酯化选择性很高。3小时和6小时后，脑和肝脏中LA和LNA的总量及其相应的标记AA和DHA代谢产物的比较表明，在这些条件下肝脏代谢对延长-去饱和的贡献可忽略不计。脑内注射[³H]DHA（22:6n-3）或[³H]AA（20:4n-6）1小时后，乙醇胺PL中分别有29.2%和12%的总放射性，而PC中分别掺入20%和40%。[³H]AA对PI的标记比在DHA存在时高6至8倍。在DG和TG组分中发现了高百分比的放射性（26.9%和18.2%）。（摘要截断于400字）
