Il a été montré que deux espèces de Parsonsia (famille Apocynaceae), qui attirent les papillons mâles de la sous-famille Danainae, contiennent des alcaloïdes du type 1,2-déhydropyrrolizidine, trouvés jusqu'à présent seulement chez les Boraginaceae; Since 1966 it has been recognized that methanol extracts of the skin of the Australian leptodactylid frogs Uperoleia rugosa and Uperoleia marmorata contain large amounts of a new peptide (uperolein) possessing a biological activity very similar to that of physalaemin. Uperolein has now been isolated in a pure form and shown to be an endecapeptide with the following sequence: Pyr-Pro-Asp-Pro-Asn-Ala-Phe-Tyr-Gly-Leu-Met-NH₂. Because uperolein differs from physalaemin only with respect to 2 amino acid residues, it may be considered as a Pro2-Ala6-physalaemin.