Rotten egg gas 'Viagra'

A smelly gas that gives rotten eggs their odour has been found to “play a key role in giving men erections”, The Independent reported. It said the scientists who made the discovery believe it could lead to the development of a new impotence drug. These results come from a study that used erectile tissue from men whose penises had been removed as part of sex-change surgery. It found that small amounts of hydrogen sulphide causes “certain muscle cells to relax, allowing blood to flow more freely into the penis, leading to an erection”.

This study has shown that hydrogen sulphide may play a role in human penile erections. However, this is early-stage research, which looked at the effects of hydrogen sulphide on human penile tissue in the laboratory rather than in a live person. Further studies will be needed to confirm whether hydrogen sulphide plays a role in erections in living humans. A better understanding of how human erections work may lead to new ways of treating erectile problems in the future, but treatments derived from this particular research are some way off.

Where did the story come from?

Dr Roberta d’Emmanuele di Villa Bianca and colleagues from the University of Naples Federico II and other universities in Italy, the UK and US carried out this research. No sources of funding were reported. The study was published in the peer-reviewed journal Proceedings of the National Academy of Sciences USA (PNAS).

What kind of scientific study was this?

This was a laboratory study using human tissue and rats. It investigated the role of hydrogen sulphide on erectile tissue from the penis. Erectile tissue is spongy tissue that fills with blood, expands and becomes hard during an erection. Hydrogen sulphide is best known as the smelly gas that causes the smell of rotten eggs. However, this chemical also exists naturally in the body, where it is thought to play a role in various processes, including the relaxation of blood vessels. Studies in animals have suggested that hydrogen sulphide is involved in penis erections, but whether it plays the same role in humans has not yet been investigated. The researchers obtained human penile tissue from six men who were undergoing sex-change surgery.

In the body, the production of hydrogen sulphide involves two proteins called CBS and CSE. These proteins make hydrogen sulphide from a precursor chemical called L-cysteine. The researchers tested whether the penile tissue contained CBS and CSE, and whether these proteins could produce hydrogen sulphide from L-cysteine. They also tried to determine where these proteins could be found in the penile tissue.

The researchers then exposed the tissue to an external source of hydrogen sulphide, or to L-cysteine, to see what would happen. They also looked at whether these effects were changed by various chemicals. Strips of penile tissue were also stimulated with electrical currents to make them contract. They then treated the contracted tissue with chemicals that stop the CBS and CSE chemicals from working (and therefore stop hydrogen sulphide from being made), and examined the effect.

Finally, they looked at the effects of hydrogen sulphide on anaesthetised rats. They injected the rats’ penises with an external source of hydrogen sulphide and monitored pressure inside the penis.

What were the results of the study?

The researchers found that the human penile tissue contained the proteins that make hydrogen sulphide (CBS and CSE), and these proteins could make hydrogen sulphide from L-cysteine. These proteins were both found in the muscle tissue of the penis, and CSE was also found in muscle tissue in the walls of the blood vessels and nerve cells of the penis.

Exposing penile tissue to an external source of hydrogen sulphide, or to L-cysteine (the precursor to hydrogen sulphide), caused the muscle in the tissue to relax. This finding supports the theory that hydrogen sulphide might play a role in facilitating erections, as relaxation of smooth muscle in the penis is necessary for an erection to occur.

Treating penile tissue with chemicals that stop the production of hydrogen sulphide enhanced the contraction of penile tissue caused by electrical stimulation. Injecting rats’ penises with a source of hydrogen sulphide caused an increase in pressure within the penis, which suggests that applying hydrogen sulphide can cause an erection.

What interpretations did the researchers draw from these results?

The researchers concluded that hydrogen sulphide is involved in muscle relaxation in human penile tissue, and therefore may be involved in facilitating erections in humans. They say that these findings may help further understand the biology of human erections, and may well lead to the development of treatments for erectile dysfunction and sexual arousal disorders.

What does the NHS Knowledge Service make of this study?

This study has shown that there may be a role for hydrogen sulphide in human penile erections. However, this is relatively early research, which looked at the effects of hydrogen sulphide on human penile tissue in the laboratory rather than in a live person. Confirmation of hydrogen sulphide's role in erections in living humans will need to come from future studies. A better understanding of how human erections work may lead to new ways of treating erectile problems in the future, but treatments derived from this particular research are some way off.