[Brain lipid metabolism during early period of global ischemia--with reference to the enzymes related to membrane phospholipid metabolism]

Abstract

It is generally known that free fatty acids (FFA) are liberated from membrane phospholipids in the brain tissue during the early period of ischemia. However, the precise mechanism of FFA liberation from phospholipids is still unclear, even though it is a central topic of neurosurgery. As an initial step toward a better understanding of the molecular mechanism, we have investigated the effects of global ischemia upon brain lipid metabolism. Brain ischemia was evoked by rat decapitation without anesthesia. Removed brains were incubated for 1, 5, 15 or 30 min at 37 degrees C and then quickly frozen in liquid nitrogen. After extraction of total lipids from the brains by Bligh & Dyer's method, the compositions of neutral lipids and phospholipids were analyzed by thin-layer and gas-liquid chromatography. For assaying deacylating enzyme (phospholipase A) activity, the brain homogenate was used as a crude enzyme. The reaction mixture including radioactive substrate, buffer (pH 7.3 & 4.0) and enzyme was incubated for 1 hour at 37 degrees C. Lipids were extracted from reaction mixture and separated by TLC. The enzyme activity was estimated by measuring the radioactivity in FFA or lysophosphatidylcholine liberated from L-alpha-di [1-14C] palmitoyl phosphatidylcholine. The reaction mixture for the assay of reacylating enzyme (acyl CoA: lysophospholipid acyltransferase) activity, contained acyl CoA, lysophosphatidylcholine, DTNB and microsomes, and the enzyme activity was determined by the amount of released CoA-SH detected spectrophotometrically. The results demonstrated that FFA, either unsaturated or saturated, rapidly accumulated in the brain during the early period of ischemia. Di-acylglycerols were also produced in the ischemic brain.(ABSTRACT TRUNCATED AT 250 WORDS)