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The Frog-Skin Pharmacist: How Vittorio Erspamer Found Brain and Gut Peptides in Amphibian Skin
Some scientists find one molecule in a career. Vittorio Erspamer, an Italian pharmacologist, found dozens, and most of them came from the skin of frogs and toads. His idea was simple: an animal that lives in water and mud needs a strong chemical defense, so its skin must be full of active compounds. He was right, and the compounds turned out to resemble signals made in our own brains and guts.
Key takeaways
- Erspamer first studied enteramine in the gut, later shown to be serotonin.
- He then moved to amphibian skin and found a series of short peptides, including physalaemin, caerulein and bombesin.
- Each one resembled a peptide that mammals make: substance P, cholecystokinin and gastrin-releasing peptide.
- He coined the word tachykinins for the fast-acting family that includes substance P.
- His approach showed that nature repeats peptide designs across species, a theme in the magainin story.
A hunch about skin
Erspamer worked at the Universities of Parma and Rome in the middle of the twentieth century. After studying a substance in the gut lining that he called enteramine, later identified as serotonin, he turned to the skin of amphibians. Frog skin glands release a mixture of compounds when the animal is threatened. Erspamer thought that those secretions would contain powerful agents that act on muscle, blood vessels and the nervous system, and he built an entire research program around testing them on strips of tissue.
Three peptides
- Physalaemin, from a South American frog, was reported in the 1960s. It made gut muscle contract and lowered blood pressure, and it resembled the substance that von Euler and Gaddum had found in horse brain, as told in the Substance P story.
- Caerulein, from the Australian green tree frog, behaved like the gut hormone cholecystokinin, stimulating gallbladder and pancreas secretion.
- Bombesin, a peptide of 14 amino acids from the European fire-bellied toad, was described in 1970. It stimulated the stomach and affected behavior when given to animals.
Twins in mammals
The big surprise was that the frog peptides led to mammalian ones. Physalaemin pointed toward substance P and its relatives, which Erspamer grouped as tachykinins. Caerulein resembled cholecystokinin. Bombesin led to the discovery of a similar mammalian peptide, gastrin-releasing peptide, isolated from pig stomach. Chemists had been unable to find these natural signals by searching mammalian tissues directly, because they were present in tiny amounts. The frog skin, with its generous supply, gave a starting point.
What the sequences taught
Comparing frog and mammal peptides showed that the business end of a peptide is often its tail. Many of these families share a conserved stretch at the C-terminus, and many end in an amide, as described in our terminal modifications post. The rest of the sequence tunes which receptor the peptide prefers.
Why it still matters
Amphibian skin is still a source of research peptides. Antimicrobial peptides, opioid-like peptides and many others have been described from it. The approach, using one species to find the key to another, is also behind modern studies of venom peptides like those in the cone snail story. Binding and activity are tested with tools such as radioligand binding and functional assays.
The bottom line
Erspamer’s skin extracts opened a window onto the gut-brain peptides that regulate digestion, feeding and pain. It is a reminder that biology repeats good designs, and that a careful observer can learn a lot from a humble source. Explore more in the Research Library.
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For laboratory research use only. Not for human or veterinary use, and not intended to diagnose, treat, cure or prevent any condition. This article is educational and is not medical advice.