Recent evidence suggests that platelet-activating factor plays a role in ischemia-induced neural injury. The Pulsinelli-Brierley four-vessel occlusion model was used to study the effect of a synthetic platelet-activating factor antagonist, BN 50739, and its solvents, either dimethyl sulfoxide or hydroxypropyl-beta-cyclodextrin, on cerebral ischemia-reperfusion. Rats were subjected to either 30 min of ischemia or 30 min of ischemia followed by 60 min of recirculation. Changes in the brain mitochondrial free fatty acid pool size, fatty acyl composition of phospholipids, and respiratory function were monitored. When the BN 50739 (2 mg of BN 50739/kg of body weight i.v.) was administered at the onset of recirculation, it significantly reversed the ischemia-induced accumulation of mitochondrial free fatty acids and loss of polyunsaturated fatty acyl chains from phosphatidylcholine and phosphatidylethanolamine while simultaneously improving mitochondrial respiration. Dimethyl sulfoxide alone decreased the mitochondrial level of malonyldialdehyde and total free fatty acid pool size, but there was no improvement in mitochondrial respiration. Hydroxypropyl-beta-cyclodextrin was reported to be pharmacologically inactive and capable of dissolving BN 50739. However, hydroxypropyl-beta-cyclodextrin alone also caused a significant increase in content of cerebral mitochondrial membrane free fatty acids and hydrolysis of phosphatidylcholine in normoxic control animals. The overall effect of BN 50739 on mitochondrial structure and energy metabolism supports the hypothesis that platelet-activating factor may play a key role in ischemia-induced cerebral injury.