Octopamine metabolism in invertebrates (Locusta, Astacus, Helix): Evidence for N-acetylation in arthropod tissues

Abstract

1. 1. Various tissues of adult Locusta migratoria, Astacus leptodactylus, Mytilus edulis and Helix pomatia were analyzed for monoamine oxidase (MAO) and N-acetyltransferase activity directed against octopamine. 2. 2. MAO activity against octopamine was detectable in Mytilus muscle and Locusta Malpighian tubules. No activity was found in any other tissue of the species studied ( Astacus not investigated). 3. 3. Low MAO activity against 5-hydroxytryptamine (5-HT) and dopamine (DA) was present in Helix tissues (about 1% of that found in rabbit tissues). 4. 4. N-Acetylation of octopamine, 5-HT and DA was prominent in Locusta nerve tissue and Malpighian tubules, and high in other locust tissues and in Astacus nerve tissue. Relatively low activity was found in skeletal muscle of these species. 5. 5. N-Acetylation of octopamine was enhanced by the addition of acetyl CoA. With 14C-labelled acetyl CoA, the label appeared in the acetylated product, which was identified as N-acetyl-octopamine. 6. 6. Addition of acetylcholine and eserine enhanced N-acetylation of octopamine in locust nerve tissue (by inhibiting cholin-acetylase which competes for acetyl CoA), but not in other locust tissues and in crayfish tissues. 7. 7. No N-acetylase activity was found in Helix and Mytilus. 8. 8. It is concluded that N-acetylation is the predominant mechanism of octopamine metabolism in arthropod tissues, particularly in the nervous system.