The French research team said these results could lead to newer pain control treatments, although other scientists were unsure of the significance of the work, stating that pain control based on this newest data is still uncertain.
The French team isolated the chemical opiorphin in human saliva, but said it may be present elsewhere in the human body. In order to study the pain-controlling effects of opiorphin, the researchers injected it into rats that had either chemically induced chronic pain or mechanically-induced acute pain.
Researchers determined that one milligram per kilogram of injectable opiorphin could suppress the pain of the rats to the same extent as a 6 milligram per kilogram dose of morphine.
The researchers surmised that the chemical opiorphin may be stopping enkaphalins -- chemicals found in the central nervous system that modify the body's response to pain -- from being destroyed.
John Wood, professor of molecular neurobiology at University College in London, said "The discovery that human saliva contains a pain-killing protein is very interesting, and follows on from the discovery of related protein activities in rats and cows. These proteins all stop the breakdown of natural morphine-like proteins that block pain pathways in the brain."
"What's particularly disturbing in this research is that rats were subjected to 'mechanically-induced acute pain.' This means that researchers used physical objects to torture the rats," said Mike Adams, a consumer health and animal rights advocate. "And it's all done in the name of profits for a pharmaceutical company. They torture rats to find a new painkiller that they can patent and sell to humans at profiteering prices," Adams said.