Brain Phospholipase A2 Is Activated After Experimental Closed Head Injury in the Rat

Abstract

Head injury was induced in rats by a weight drop device, falling over the left hemisphere. The rats were killed at 15 min, 4 h, and 24 h after injury. Cortical slices were taken from the injured zone, from the corresponding region of the contralateral hemisphere, and from the frontal lobe of both hemispheres. These cortical slices were incubated in the presence of a fluorescent phospholipid analogue, 1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)aminocaproylphosphatidylcholine (C6-NBD-PC) which is a substrate for phospholipase A2 (PLA2) in intact cells. The interaction of this substrate with cells produces only one fluorescent product, the fatty acid C6-NBD-FA, released from the 2 position of C6-NBD-PC. Thus, the level of C6-NBD-FA produced is a direct measure of PLA2 activity. Fifteen minutes after trauma, a 75% increase of PLA2 activity was found in the injured zone. At 4 h, the frontal lobe of the contused, left hemisphere had elevated PLA2 activity, as well as the injured zone (92 and 81%, respectively). At 24 h, PLA2 activity at the site of injury was 245% of sham. In the right, noninjured zone, no significant changes in PLA2 activity were noticed during the entire time course of the experiment. Prostaglandin E2 (PGE2) was extracted from the same cortical slices as those used for PLA2 activity measurement. A significant correlation (Pearson coefficient test, correlation coefficient = 0.469, p < 0.05, n = 21) was found between the elevation of PLA2 activity and PGE2 levels measured in the injured hemisphere, at 4 and 24 h. The elevation of PGE2 production induced by the trauma was abolished when the rats were pretreated with dextran 70,000, which has been previously shown to inhibit PLA2 activity. The results of this study support the hypothesis that activation of brain PLA2 is involved in the increased cerebral production of eicosanoids induced by trauma.