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Eleven peptides have been isolated from the skin glands of the ‘buzzing tree frog’ Litoria electrica. The two most abundant peptides are tryptophyllin L 3.1 [Phe Pro Trp Pro (NH2)] and electrin 1 [Phe Val Pro Ile Tyr Met (NH2)]. These peptides show neither significant antimicrobial nor smooth muscle activity. Tryptophyllin L 3.1 is thought to be a neuromodulator or neurotransmitter, and it is similar in structure to the human endomorphins [e.g. Tyr Pro Trp Phe (NH2)] which act on the γ-receptor. Both Litoria electrica and the ‘red tree frog’ Litoria rubella produce tryptophyllin peptides: it is considered that both species evolved from the same ancestor.

Seventeen peptides have been isolated and characterized from specimens of the red tree frog 'Litoria rubella', collected from 15 locations throughout Australia. These can be classified into two families of peptides, viz. ( i ) the tryptophyllins L, of which Phe Pro Trp Leu (NH2), Phe Pro Trp Pro (NH2) and pGlu Phe Pro Trp Pro (NH2) are the major constituents, (ii) two types of rubellidins, the first of which is unique to 'Litoria rubella' [e.g. Val Asp Phe Phe Ala (OH)], and the second [e.g. Gly Leu Gly Asp Ile Leu Gly Leu Leu Gly Leu (NH2)], containing peptides of the caeridin type (like those isolated from Litoria caerulea and Litoria splendida). These peptides show no significant antimicrobial activity. The tryptophyllins are thought to be neuromodulators or neurotransmitters, but the roles of the anionic rubellidin peptides in the amphibian integument are not understood. A comparison of the skin peptide profiles of live specimens of 'Litoria rubella' collected from different locations suggests that there are a number of discrete populations (perhaps different species or subspecies) in ( i ) an area from Kakadu National Park to the Adelaide River in the Northern Territory, (ii) in and around Alice Springs, (iii) in the north of South Australia, and (iv) in several areas of the Kimberley region of Western Australia. In addition, there appear to be evolving populations along the eastern seaboard of Queensland.