Indole-, imidazole- and phenyl-alkylamines in the skin of one hundred and forty American amphibian species other than bufonids.

Extracts prepared from dried or fresh skins of 140 American amphibian species, other than bufonids, were subjected to chemical and biological screening in order to determine the presence and concentrations of aromatic biogenic amines. The most frequent and abundantly occurring amine category was that of indolealkylamines, represented by their prototype 5-hydroxytryptamine and its N-methylated derivatives. Conjugated and cyclized indolealkylamines, typical for the toad skin, were apparently lacking. Phenylalkylamines were represented by two quaternary ammonium bases: leptodactyline and, very rarely, candicine. Leptodactyline was particularly abundant in leptodactylid frogs of the genus Leptodactylus. Histamine occurred in trace amounts in different species, in large amounts only in some Leptodactylus species of the "pachypus" section. On the other hand, N-methylated histamines and cyclized histamines (spinaceamines) were confined to the skin of Leptodactylus pentadactylus labyrinthicus. The possible taxonomical and evolutionary significance of amphibian skin amines is pointed out.