THG315 was a gift from Theratechnologies, Inc. (Saint-Laurent, Québec), CGS12970 from Ciba-Geigy (Summit, NJ), and L-670596 from Merck-Frosst (Kirkland, Québec, Canada). Human brain endothelial cells were generously provided by the National Research Council of Canada (Ottawa, Ontario, Canada). The following materials were purchased: human aortic, dermal and umbilical vein endothelial cells (Clonetics, San Diego, CA); C-PAF (1-O-hexadecyl-2-N-methylcarbamyl-sn-glycero-3-phosphocholine), BN52021 (Ginkolide B), CV-3988, and PCA-4248 (Biomol Research Laboratories, Inc., Plymouth Meeting, PA); poly-l-lysine, ceramide, dimethyl sulfoxide (DMSO), nicotinamide, 3-(4,5-dimethyl thiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT), and propidium iodide (PI; Sigma Chemical Co., St. Louis, MO); Hoechst 33342 (Polysciences, Warrington, PA); antifade reagent (Fluoroguard; Bio-Rad Laboratories, Hercules, CA); platelet-activating factor scintillation proximity assay kit (Amersham, Oakville, Ontario, Canada); antibodies to factor VIII, smooth muscle-specific actin, and glial fibrillary acetic protein (GFAP; Dako, Carpinteria, CA); FITC-conjugated goat anti-rabbit antibody (Jackson ImmunoResearch Laboratories, West Grove, PA); PAF receptor antibody (Cayman Chemicals, Ann Arbor, MI); a direct fluorescein kit (Apoptag; Intergen, Gaithersburg, MD); Z-DEVD-FMK and Z-VAD-FMK (R&D Systems Inc., Minneapolis, MN); Hamilton syringe (Hamilton Co., Reno, NV); annexin-V-FITC kit (Biosource, Camarillo, CA); 1-O-octadecyl,[octadecyl-9,10-3H(N)]-2-acetyl-sn-glyceryl-3-phosphorylcholine (specific activity: 160 Ci/mmol; NEN Life Science Products, Inc., Boston, MA); other materials were purchased from Fisher Scientific (Montréal, Québec, Canada).