by Whit Gibbons

August 20, 2006

I asked University of Georgia graduate student Brian Todd to respond to this two-part question: What good are frogs and why should ecologists study them? He titled his reply "The Frog Pharmacy."

"For many people, the connection between frogs, research, and human society may seem tenuous at best. Beyond remembering (not always fondly) the frog they dissected in biology class, most people would be hard put to describe even a single contribution frogs have made to humankind. But frogs have played an important, though little-known, role in scientific endeavors for many years. And current research suggests they will continue to do so.

"In the 1930s, frogs were important contributors to the medical field. Well before the advent of modern pregnancy tests, two scientists discovered that the African clawed frog could be used to test for pregnancy in women. In the next two decades, tens of thousands of these animals were imported from their native Africa as hospitals in North America began stocking them for use in early, rapid pregnancy detection.

"More recently, scientists have discovered that most frog species produce skin secretions of amino acid compounds called peptides. These peptides help protect frogs' otherwise sensitive and porous skin from bacterial and fungal infections. Some even discourage predators, which find the peptides distasteful. The discovery of these peptide secretions and their properties has produced several avenues of research with applications for human medicine.

"One research team from the United Kingdom has identified an important set of antibiotics in the skin of an Australian tree frog. These scientists have discovered that the peptides from the tree frog kill bacteria that are resistant to conventional antibiotics. Modern medicines typically combat bacteria by targeting vital enzymes, to which the bacteria can develop a resistance, an increasingly alarming problem in modern medicine. The frog peptides eliminate bacteria by dismantling bacterial cell membranes, making the frog-derived antibiotics more permanently effective.

"In other developments, the poison from a beautiful but deadly South American poison dart frog is finally being thoroughly analyzed for use as a painkiller. In 1976, extract from the skin of a rare frog from Ecuador was found to be more effective than morphine at blocking pain but was also highly toxic to most animals. The difficulty in isolating and identifying the precise chemical compound responsible for the painkilling effect among the suite of toxic compounds present in the frog’s skin secretions prevented it from being thoroughly evaluated. However, in 1998, researchers with the National Institutes of Health used new analytical tools to decipher the chemical structure of the compound, leading to the discovery of a new drug more effective than morphine with fewer negative side effects.

" By some estimates, as many as 40 million Americans depend on morphine for pain relief for medical conditions and postoperative pain treatment. However, side effects from morphine, such as dependency and heart and respiratory problems, have long plagued its use and application. With the discovery of the new compound ABT-594, which lacks these serious side effects, many millions of Americans who suffer from pain may look forward to brighter futures.

"Frogs may soon make another contribution to human society that would provide relief to many people. A team of researchers led by Craig Williams of the University of South Australia has begun testing the application of frog skin secretions as a mosquito repellant. The scientists have demonstrated that certain natural compounds in frog skin secretions repel mosquitoes--welcome news for people who enjoy outdoor activities in the warmer months but worry about using chemical repellants.

"Frogs and toads stand to make even more contributions to human society as scientists continue to investigate the thousands of unstudied chemical compounds present in their skin secretions. As Craig Williams put it, 'Frog skin is really a portable pharmacy.' And the next few years may see products developed from research on frogs that fill our own pharmacies.

"Finally, for many folks the sheer enjoyment derived from listening to the seasonal songs of frogs is enough. Whether you appreciate frogs for their intrinsic value or for their other fine contributions, they are welcome friends."

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