Italian scientists say they may have discovered a 'natural Viagra' in a pungent gas emitted by hot springs.
Hydrogen sulphide (H2S), sometimes called stink damp or rotten-egg gas, is found at many hot spas in Italy and elsewhere.
Despite its unpleasant smell, it has been commonly believed, especially in Italy since Roman times, to have medicinal properties.
This belief has been bolstered by recent studies which found that it was able to widen blood vessels.
The new, two-year Italian study found that these same 'vasodilatory' effects can be achieved to combat impotence just like Viagra.
The tests were performed by researcher Roberta d'Emmanuele di Villa Bianca under the guidance of Naples University pharmacology chief Giuseppe Cirino, Naples clinical urology researcher Vincenzo Mirone, and a Nobel prizewinning American pharmacologist, Louis Ignarro of the University of California at Los Angeles (UCLA).
First, they identified two enzymes in the human penis, CBS and CSE, which turn a common amino-acid (L-Cys) into the gas.
Second, they found that the gas caused blood vessels to expand in human penis tissue in test tubes.
Third, it caused erections in lab rats.
''The discovery could lead to the development of a new therapeutic target against impotence,'' said the study, published in the Proceedings of the National Academy of Sciences (PNAS).
UCLA's Ignarro won his Nobel Prize for Medicine in 1998 for discovering the importance of another naturally occurring gas, nitric oxide, for the human cardiovascular system.
