Platelet aggregation is thought to be involved in renal pathology through induction of the intraglomerular coagulation that leads to subsequent glomerular damage. Thromboxane A2 (a potent pro- aggregatory substance) is the major cyclooxygenase product of arachidonic acid metabolism in the platelet. Thus, activation of this pathway results in stimulation of the aggregatory process. However, little is known about the consequences of the cytochrome P-450 route of arachidonic acid metabolism. A recent study has highlighted the possibility that the products of cytochrome P-450 mediated arachidonic acid metabolism can regulate platelet activation. The purpose of the proposed study is to assess the possible involvement of this pathway in human platelet activation. First, the profile of cytochrome P-450 metabolism in human platelets will be determined and the possibility that the arachidonic acid epoxides (EETs) are major endogenous products of the human platelet will be assessed. It is envisaged that this study will be carried out by the use of human platelets pre- labelled with 3H-arachidonic acid. Structural characterization will be made by the use of mass spectrometry. The profile of released products will be examined in response to three different agonists: thrombin, epinephrine and platelet activating factor. Second, a quantitative assessment of EET release by human platelets in response to the three agonists will be made. It is envisage that techniques we have developed recently based on stable isotope dilution gas chromagraphy/negative ion chemical ionization mass spectrometry will be used in these studies. Third, the localization of EET esterified in the various lipid pools will be determined. This letter aim will be accomplished by a strategy based on high performance liquid chromatography and mass spectrometry. This method was recently developed for the characterization of EETs esterified in rat liver. Fourth, the mechanism by which the EETs are synthesized and release will be explored. Finally, the mechanism by which the EETs themselves inhibit platelet aggregation will be explored. These studies will have relevance to understanding a novel mechanism by which platelet function can be modulated by endogenous lipids. It is envisaged that this will help designing interventions to protect function in disease states where platelet stimulated coagulation is thought to play an important role.