Arachidonic acid and its metabolites during cerebral ischemia and recirculation. Pharmacological interventions

Complement depletion does not reduce brain injury in a rabbit model of thromboembolic stroke

The contribution of the complement system to cerebral ischemic and ischemia/reperfusion injury was examined in a rabbit model of thromboembolic stroke by delivery of an autologous clot embolus to the intracranial circulation via the internal carotid artery. A two-by-two factorial design was employed to study the impact of complement depletion via pretreatment with cobra venom factor (CVF, 100 U/kg i.v.) in the setting of permanent (without tissue plasminogen activator; t-PA) and transient (with t-PA) cerebral ischemia. Thirty-two New Zealand white rabbits were assigned to one of four groups (n=8, each group): control without t-PA, control with t-PA, CVF without t-PA and CVF with t-PA. In the complement intact animals, t-PA administration resulted in an approximate 30% reduction in infarct size when compared to the group not receiving t-PA (20.4+/-6.6% of hemisphere area vs. 30.1+/-7.2%; mean+/-SEM). However, infarct sizes in the complement depleted rabbits, with (30.7+/-8.2%) or without (30.2+/-7.9%) t-PA, were no different from the control group receiving no therapy. Similarly, no difference in regional cerebral blood flow or final intracranial pressure values was noted between any of the four groups. Complement activation does not appear to be a primary contributor to brain injury in acute thromboembolic stroke.

Effect of ibuprofen on regional eicosanoid production and neuronal injury after forebrain ischemia in rats

Post-ischemic metabolism of arachidonic acid by cyclooxygenase results in the elaboration of numerous eicosanoids and in the generation of free radicals. Accordingly, the effect of cyclooxygenase inhibition by ibuprofen on post-ischemic eicosanoid production and delayed neuronal death was evaluated in Wistar-Kyoto rats subjected to incomplete forebrain ischemia. In control (C) and ibuprofen-treated groups (n = 5 each), pre- and post-ischemic eicosanoid production in the caudate nucleus (CN) and dorsal hippocampus (HPC) were evaluated by microdialysis. The ibuprofen-treated animals were given ibuprofen, 15 mg/kg i.v., prior to insertion of microdialysis probes. Forebrain ischemia was induced by bilateral carotid artery occlusion (BCAO) for 10 min with simultaneous hypotension to 35 Torr. The concentrations of thromboxane B2 (TxB2), 6-keto-PGF1 alpha and PGF2 alpha in the microdialysate were measured by radioimmunoassay. In two additional concurrent groups of rats (n = 10 each), neuronal injury in the HPC, CN and cortex (parietal, temporal and entorhinal regions) was evaluated histologically three days after 10 min of forebrain ischemia with and without pre-ischemic ibuprofen administration. In the control microdialysis group, levels of TxB2, 6-keto-PGF1 alpha and PGF2 alpha increased in both CN and HPC after probe insertion. These probe related increases were substantially reduced in the ibuprofen group. After ischemia and reperfusion in the control group, the levels of TxB2 and PGF2 alpha increased in both CN and HPC. Levels of 6-keto-PGF1 alpha increased in the CN but not in the HPC. The administration of ibuprofen substantially reduced post-ischemic TxB2 and PGF2 alpha levels in both CN and HPC and decreased 6-keto-PGF1 alpha levels in the CN. The results of these initial microdialysis studies left the possibility that, in the ibuprofen group, the reduction in eicosanoid levels after probe penetration might have influenced the subsequent post-ischemic eicosanoid production. Therefore, in an additional group of animals (n = 5), ibuprofen was administered after probe insertion. Only PGF2 alpha levels were measured in this group. Increased levels of PGF2 alpha comparable to the original control group were detected after probe penetration. Nonetheless, after ibuprofen administration, the pre- and post-ischemic levels of PGF2 alpha were again significantly reduced. In the histologic evaluation groups, overall neuronal injury was significantly less in the ibuprofen treated animals. This protective effect of ibuprofen was most clearly evident in the CA3 sector of the HPC.(ABSTRACT TRUNCATED AT 400 WORDS)

Eicosanoid production in the caudate nucleus and dorsal hippocampus after forebrain ischemia: a microdialysis study

Thromboxane (Tx)B2 and 6-keto-prostaglandin (6-keto-PG) F1 alpha formation in the hippocampus and caudate nucleus were evaluated by microdialysis during and following forebrain ischemia. Spontaneously hypertensive rats were subjected to bilateral carotid artery occlusion with simultaneous hypotension for 8, 14, or 20 min. Dialysate was collected during the ischemic interval and during the reperfusion period. TxB2 and 6-keto-PGF1 alpha levels were measured by radioimmunoassay. In both structures, TxB2 production increased significantly during the reperfusion period in all three ischemic groups. By contrast, increased 6-keto-PGF1 alpha elaboration was observed after only the longest ischemic duration. While TxB2 levels gradually decreased during the 3-h reperfusion period in all groups, the levels in the group subjected to 8 min of ischemia returned to control values most rapidly. A relationship between the duration of ischemia and TxB2 production was therefore evident. 6-Keto-PGF1 alpha levels increased in only the group subjected to 20 min of ischemia and, by contrast to the pattern of TxB2 change, 6-keto-PGF1 alpha levels remained elevated throughout the reperfusion period. During reperfusion, the ratio of TxB2 to 6-keto-PGF1 alpha increased substantially versus the preischemic period in both structures. The data demonstrate that eicosanoid elaboration following cerebral ischemia can be evaluated by the microdialysis technique. In addition, they indicate that the thresholds (duration of ischemia) for the postischemic production and the temporal profiles of TxB2 and 6-keto-PGF1 alpha in the caudate and hippocampus differ. They also demonstrate that there is regional heterogeneity in the patterns of eicosanoid elaboration after forebrain ischemia.