Possible involvement of arachidonic acid and eicosanoids in metamorphic events inHydractinia echinata (Coelenterata; hydrozoa)

Abstract
Upon induction of metamorphosis, larvae of the marine hydroid Hydractinia echinata release [14C]‐arachidonic acid from previously labeled endogenous sources. The lipoxygenase inhibitors nordihydroguaiaretic acid and 5,8,11,14‐eicosatetraynoic acid inhibited metamorphosis induced by Cs+ and 1,2‐sn‐dioctanoylglycerol, whereas the inhibitors of cyclooxygenase, indomethacin, and acetylsalicylic acid were ineffective, suggesting a role for lipoxygenase metabolites of arachidonic acid in induction of metamorphosis. Lipoxygenase products in Hydractinia echinata were isolated and identified by gas chromatography/mass spectrometry. 8‐ and 12‐HETE were the most abundant metabolites. In cytosolic fractions from larvae activity of an arachidonic acid metabolizing enzyme, presumably a lipoxygenase, was found. The metabolic product was identified by 1H‐NMR and chiral phase HPLC as 8(R)‐HETE. Its production was strongly inhibited by NDGA, but not by indomethacin.