In vertebrates, the cardiovascular effects of bufadienolides and
bufotoxins have been attributed to their ability to increase cardiac contractility and decrease cardiac rate by inhibiting the [Na.sub.+]/[K.sup.+]-ATPase pump in a manner similar to digoxin (Chen & Kovarikova, 1967; Sakate & Oliveira, 2000).
Toad toxin mainly consists of derived steroids (bufadienolides and
bufotoxins) and biogenic amines (epinephrine, norepinephrine, serotonin, bufotenine, and dihydrobufotenine) [3-6].
These include
bufotoxins and larval skin extracts with antipredatory functions, which evoke alarm responses in toad tadpoles.
Bufonid parotoid macroglands, largely known by their toxic secretions, contain
bufotoxins that, in contact with the oral mucosa of the predators, may present cardiac glycosidelike activity, increasing the contractile force of the heart [11].