Men may be better than women at tolerating pain because of a key protein, scientists have proposed.

Its presence may explain the controversial finding that men have a higher pain threshold than women.

It's a gross oversimplification to say there's a gender difference in response to pain Prof David Rowbotham

The latest evidence is based on studies of laboratory mice carried out by a team at the University of California in San Francisco.

Some experts have dismissed the research however, saying pain is much more complex in people.

The US researchers found male mice lacking a protein called GIRK2 had a lower pain threshold than normal.

There was no difference in female mice with the same mutation, however.

This suggests that the molecule plays a sex specific role in transmitting pain signals.

Tailored treatments

The research results were published in the Proceedings of the National Academy of Sciences.

The team, led by Dr Igor Mitrovic, said: "Given that some pain syndromes require multi-drug treatments for the control of pain, these studies provide information for rationally based differential processes in men and women."

Experts say it will be a long time before 'his and hers' pain relief becomes a reality.

According to Dr Trevor Bushell of Strathclyde University in Glasgow, there is some evidence that men and women react to pain differently but it needs further research.

"Pain is a lot more complex in humans than animals," he told BBC News Online.

Dr Bushell, of the department of physiology and pharmacology at Strathclyde, said gender specific painkillers were theoretically possible.

It will take a great deal of work, however, to identify the different receptors and pathways involved in pain control in men and women.

'Multi-dimensional'

David Rowbotham, Professor of Pain Management and Anaesthesia at the University of Leicester, said pain differed widely depending on the context.

Pain caused by cancer, for example, is very different to that caused by physical injuries such as a broken leg.

It also has an emotional context and cannot be measured in the same way as, say, blood pressure or other physiological signs.

"It's a gross oversimplification to say there's a gender difference in response to pain," he told BBC News Online.

"Pain is a multi-dimensional thing and it depends on the context you're looking at."