Cerebral ischemia induced quantitative changes in rat brain membrane lipids involved in phosphoinositide metabolism

The content and acyl group composition of phosphatidylinositol, poly-phosphoinositides, diacylglycerols, phosphatidic acids, and free fatty acids in rat brain homogenates of cerebral cortex and subcellular fractions were examined with respect to a 2 min post-decapitative ischemic treatment. With the exception of free fatty acids, these lipids are involved in the cyclic event associated with the receptor-mediated poly-phosphoinositide turnover. The ischemic treatment elicited a decrease in poly-phosphoinositide level in brain homogenates, synaptosomes, plasma membranes, and microsomes but not in myelin, and an increase in diacylglycerols, which was observed in brain homogenates and synaptosomes but not in other subcellular fractions. On the other hand, the level of phosphatidylinositol was not altered. The acyl groups of phosphoinositides are enriched in stearic and arachidonic acids. The diacylglycerols and free fatty acids that accumulated during the ischemic treatment are also enriched with the same fatty acids. There is a decrease in phosphatidic acid level after the ischemic treatment, but the change was only found in brain homogenates and synaptosomes. Therefore, the diacylglycerols increased during the ischemic treatment may be derived from hydrolysis of poly-phosphoinositides and phosphatidic acids. However, the amount of poly-phosphoinositides degraded is not enough to account for both diacylglycerols and free fatty acid increase.