Abstract
The ichthyotoxin from Prymnesium parvum caused a slow contraction of the guinea-pig isolated ileum preparation, followed by decreased sensitivity to acetylcholine and to 5-hydroxytryptamine. These effects were reversed by washing. Administration of toxin was followed by insensitivity to further toxin. It was possible that a cholinergic transmitter participated in the contractions of the gut as this action was reduced both by atropine and by morphine. Illumination with visible light or warming a solution of toxin destroyed its antiacetylcholine activity before abolishing its stimulant action on gut. The crude extract of Prymnesium parvum may contain a mixture of active substances with different pharmacological actions.
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