Cardiovascular effects of an organophosphate toxin isolated from Ptychodiscus brevis.

The dose-dependent hypotensive and bradycardic effects induced by an ichthyotoxic organophosphate compound isolated from the marine dinoflagellate Ptychodiscus brevis were studied. These effects were not antagonized by atropine, but potentiated by alpha-adrenoceptor blocker and hexamethonium. The toxin abolished the vasopressor effect elicited by phenylephrine, indicating an alpha-adrenergic blocking activity. The cardiovascular depressor responses were antagonized by tetraethylammonium while blockade of cholinergic and histaminergic receptors or inhibition of prostaglandin synthesis failed to modify these effects. The results indicate that the cardiovascular depressor effects of the toxin are probably mediated through alpha-adrenergic and ganglionic blockade accompanied by modulation of potassium channel activity.