Small quantities of hydrogen sulphide are released by nerve cells in the penis before intercourse, causing the male sex organ to become erect, Italian scientists have found.
The foul-smelling gas is released in larger amounts by decaying eggs and from the exhaust pipes of cars fitted with catalytic converters, but researchers now believe it could be used to create a rival to Viagra.
"We found that hydrogen sulphide is involved in human penile erection," Professor Giuseppe Cirino of the University of Naples Federico II told The Independent.
"The hydrogen sulphide pathway represents a new therapeutic target for erectile dysfunction and it should be possible in future to deliver drugs that either deliver hydrogen sulphide or that control the hydrogen sulphide production."
A similar discovery about the role of another chemical, nitric oxide, in causing erections eventually led to the development of Viagra, which stimulates blood supply to the penis.
Around a third of men to not react to that anti-impotence drug and they could benefit from a new medication based on hydrogen sulphide, Prof Cirino told the newspaper.
The research, which was based on tests carried out on erectile tissue removed from eight male-to-female transsexuals who had their sex organs removed, was published in the journal Proceedings of the National Academy of Sciences
