Conversion of 1-alkyl-2-acetyl- [formula omitted] to platelet activating factor and related phospholipids by rabbit platelets

Abstract

The metabolic pathway for 1-alkyl-2-acetyl- sn - glycerols , a recently discovered biologically active neutral lipid class, was elucidated in experiments conducted with rabbit platelets. The total lipid extract obtained from platelets incubated with 1-[1,2- 3H]alkyl-2-acetyl- sn - glycerols or 1-alkyl-2-[ 3 H]acetyl- sn - glycerols contained at least six metabolic products. The six metabolites, identified on the basis of chemical and enzymatic reactions combined with thin-layer or high-performance liquid chromatographic analyses, corresponded to 1-alkyl- sn - glycerols , 1-alkyl-2-acetyl- sn - glycero-3-phosphates, 1-alkyl-2-acyl(long-chain)- sn - glycero-3-phosphoethanolamines, 1-alkyl-2-acetyl- sn - glycero-3-phosphoethanolamines, 1-alkyl-2-acyl(long-chain)- sn -glycero-3-phosphocholines, and 1-alkyl-2-acetyl- sn - glycero-3-phosphocholines (platelet activating factor). These results indicate that the metabolic pathway for alkylacetylglycerols involves reaction steps catalyzed by the following enzymatic activities: choline- and ethanolamine-phosphotransferases, acetyl-hydrolase, an acyltransferase, and a phosphotransferase. The step responsible for the biosynthesis of platelet activating factor would appear to be the most important reaction in this pathway and this product could explain the hypotensive activities previously described for alkylacetyl-(or propionyl)-glycerols. Of particular interest was the preference exhibited for the utilization of the 1-hexadecyl-2-acetyl- sn - glycerol species in the formation of platelet activating factor.