Arachidonic acid metabolites are postulated to play a role in the pathogenesis of cerebral ischemia. In order to test the development of lipoxygenase metabolites of arachidonic acid in cerebral ischemia, we measured free arachidonic acid and slow reacting substance of anaphylaxis (SRS-A) and leukotriene C4 in the brain tissue. Moreover, we studied the influence of inhibitor of SRS-A release on postischemic cerebral edema. Severe forebrain ischemia in rats was induced by the modification of the method described by Pulsinelli and Brierley. Both vertebral arteries were electrocauterized through the alar foramen and then bilateral common carotid arteries were clamped by aneurysmal clips and mean arterial pressure was reduced to 80-90 mmHg. EEG activity was isoelectric throughout the period of carotid clamping. After forebrain ischemia had been maintained for 30 minutes, recirculation was started by removal of the arterial clamps and by increasing blood pressure to the preischemic level. Following the desired ischemic or postischemic periods, the brains were frozen in situ with liquid nitrogen. The brains were then chiselled out during irrigation with liquid nitrogen and stored at -80 degrees C until analysis. The brain extracts were analysed by high performance liquid chromatography for free arachidonic acid, by bioassay using the ileum of guinea pig for SRS-A and by radioimmunoassay for leukotriene C4. Brain water content was calculated with dry weight method. Inhibitor of SRS-A release, tranilast, was given intraperitoneally, 100 mg/kg 30 minutes before induction of ischemia and 50 mg/kg immediately before recirculation.(ABSTRACT TRUNCATED AT 250 WORDS)