Identification and hatching factor activity of monohydroxyeicosapentaenoic acid in homogenates of the barnacle Elminius modestus

A crude eicosanoid extract of the barnacle Elminius modestus caused hatching of isolated egg masses from both E. modestus and Balanus balanoides . On thin-layer chromatography (TLC) two bands containing hatching factor activity were identified, a monohydroxy fatty acid (MHFA) band with potent hatching factor activity and a less active trihydroxy fatty acid (THFA) band. Gas chromatography-mass spectrometry (GC-MS) of the MHFA band showed that it consisted mainly of positional isomers of monohydroxyeicosapentaenoic acid, predominantly 8-hydroxyeicosapentaenoic acid (8-HEPE). A range of positional isomers of monohydroxyeicosapent­aenoic acid was produced by autoxidation of the methyl ester and this mixture was highly active in hatching E. modestus eggs. The commer­cially available stereoisomer 8( S )-HEPE hatched E. modestus eggs at concentrations as low as 10 -8 M. The saturated derivative 8-hydroxyeicosanoic acid did not show hatching factor activity.