The secret of successful sex

It's all down to chemicals

Scientists have worked out how the male erection is maintained.

They hope the discovery will lead to new treatments for impotence.

A team from Johns Hopkins University in Baltimore discovered ten years ago that an erection is caused when an erotic thought or physical sensation triggers the release of nitric oxide from the nerve endings in the penis.

The physiology of erection is like driving a car

Dr Arthur Burnett

This stimulates the blood flow that leads to the swelling of the tissues. However, that response lasts for only a few seconds.

Now a team from the same university has discovered how an erection, once formed is maintained.

By studying mice and rats in the laboratory they have discovered that the key is the continued production of nitric oxide by the blood vessels.

Hit the accelerator

Researcher Dr Arthur Burnett said: "The physiology of erection is like driving a car.

"You can't just turn the key and expect to go anywhere. You also need to hit and hold the accelerator."

Essentially, the blood vessels take over from the nerves after the first flush of excitement, releasing a continual supply of nitric oxide and thereby hardening and maintaining the erection.

Dr Burnett said: "Once blood starts flowing into the penis, the source of nitric oxide in the blood vessels is continuously activated so that more nitric oxide is released, more tissue relaxes, more blood comes in and a sustained erection is achieved."

The flow of blood creates a minor stress on the blood vessel wall, which activates the release of more nitric oxide from the endothelial cells of the blood vessel wall.

The source of nitric oxide in the blood vessel is an enzyme called endothelial nitric oxide synthase, which until now had been the missing piece of the puzzle.

The research is published in the Proceedings of the National Academy of Sciences.