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 .