The enantiomer and the positional isomer of platelet-activating factor

Abstract We have compared for rabbit platelet aggregating and desensitizing activity two different preparations of platelet-activating factor (PAF-acether) (1- O -alkyl-2- O -acetyl- sn -glycero-3-phosphocholine) and of its enantiomer (3- O -alkyl-2- O -acetyl- sn -glycero-1-phosphocholine). After phospholipase A 2 treatment, the unnatural enantiomers appeared about 3000-fold less active than PAF-acether, a result which definitively establishes the stereopecificity of the mode of action of this mediator. A new structural analog of PAF-acether, 1- O -hexadecyl-3- O -acetyl- sn -glycero-2-phosphocholine, was isolated and characterized. It was a weak platelet agonist, stressing further the importance for PAF-acether activity of the acetyl group at position 2 of the glycerol.