PAF-like activity of O-acetylated sphingomyelin.

Abstract

O-acetylated sphingomyelin (Ac-SM) was found to cause aggregation of rabbit platelets in vitro. The Ac-SM-induced aggregation was accompanied by subsequent desensitisation of platelets to platelet-activating factor (PAF). The activity of Ac-SM exceeded that of acyl-PAF by about fourfold. BN 52021, a specific PAF-receptor antagonist, was found to inhibit the Ac-SM-induced aggregation. These results, together with earlier reports that sphingomyelin can inhibit the effects of PAF, suggest a new physiological function for sphingomyelin as a regulator of PAF-receptor binding. A search for enzymes to catalyse specifically the acetylation and deacetylation of sphingomyelin is required to confirm the physiological existence of sphingomyelin derivatives.