Intravenous injection of [1-14C]arachidonate to examine regional brain lipid metabolism in unanesthetized rats.
We examined the metabolic disposition and brain distribution of an unsaturated fatty acid, [1-14C]arachidonate, between 5 and 240 min following its intravenous bolus injection in unanesthetized adult rats. Injected [1-14C]arachidonate was cleared rapidly from plasma, with less than 10% remaining by 2 min. Total brain radioactivity, 0.2% of the injected dose, was near maximal by 5 min, reached a peak by 15 min, then slowly declined. Radioactivity in brain lipids constituted greater than 82% of the total brain radioactivity at all times. Radioactivity in aqueous-soluble metabolites was greatest at 5 min (13% of total) and declined to 5% by 240 min. Protein pellet-associated radioactivity gradually rose to a peak of 7% by 120 min. Within the lipid fraction, more than 92% of radioactivity was in glycerolipids, with greater than 81% in phospholipids. Radioactivity in inositol phosphoglyceride was maximal at 5 min (47% of phospholipid radioactivity); and declined to 34% by 20 min, whereas radioactivity in choline phosphoglyceride peaked at 15 min (41% of phospholipid radioactivity) and was constant thereafter. In contrast, radioactivity in ethanolamine phosphoglycerides increased from 7 to 17% during the course of the experiment. Quantitative autoradiography of brain sections indicated incorporation of [1-14C]arachidonate into gray-matter regions was 1.5- to threefold that into white-matter regions. The data were analyzed in terms of a model for brain fatty acid uptake from plasma. Estimates of unidirectional transfer constants, k, for [1-14]arachidonate from plasma to brain regions with an intact blood-brain barrier ranged from 0.0005 to 0.0015 ml.sec-1.g-1 and were correlated with those for [9,10-3H]palmitate. The results indicate that brain phospholipid metabolism in awake animals can be examined regionally and quantitatively using intravenous injection of [1-14C]-arachidonate combined with quantitative autoradiography and biochemical analysis.
DeGeorge
J J
JJ
Laboratory of Neurosciences, National Institute on Aging, Bethesda, Maryland.
Noronha
J G
JG
Bell
J
J
Robinson
P
P
Rapoport
S I
SI
D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism / Q000493:pharmacokinetics*; D001921:Brain / Q000378:metabolism*; D007275:Injections, Intravenous; D008297:Male; D010743:Phospholipids / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344
D001095:Arachidonic Acids; D010743:Phospholipids; D016718:Arachidonic Acid