5-Hydroxytryptamine in Coelenterates

Abstract

IN an earlier report¹, it was concluded from evidence obtained by pharmacological tests and paper chromatography that 5-hydroxytryptamine was a constituent of the sea-anemones, Metridium senile and Calliactis parasitica. More 5-hydroxytryptamine-like material was obtainable from Metridium tentacles, with their nematocysts, than from body wall which is relatively free of nematocysts. This led to the suggestion that 5-hydroxytryptamine might be a pain-producing factor in these stinging organelles. An independent study² of material released on discharge of isolated Metridium nematocysts yielded two hydroxyindoles tentatively identified by chromatography as 5-hydroxytryptophan and bufotenine. The identification of 5-hydroxytryptamine in Calliactis has now been made quite certain^3,4. However, the very large amount found in the coelenteric organ of this species and the relatively small amount in tentacles, coupled with the finding of little 5-hydroxytryptamine in Metridium and Anemonia sulcata, led Mathias, Koss and Schachter^3,4 to conclude that it is unlikely that 5-hydroxytryptamine is associated with nematocysts. Further evidence is now available that this conclusion may not be fully warranted.