Abstract

In the innervated pump-perfused hind leg of the cat and in the innervated pump-assisted cross-perfused hind leg of the cat, saxitoxin causes a vasodilation by a direct relaxant action on the vascular muscle (at doses lower than 1.5 µg/kg) and by an additional blockade of vasoconstrictor nerves (at doses higher than 1.5 µg/kg). These actions of saxitoxin are similar to those of tetrodotoxin. Saxitoxin differs from tetrodotoxin in causing a less severe hypotension, which is accompanied by a greater tendency for compensatory release of catecholamines. This tendency is responsible for the frequent occurrence of a secondary pressor effect after saxitoxin hypotension and may account for the apparent absence of hypotension in clinical cases of paralytic shellfish poisoning.