Why do some people have a high tolerance for pain, while others experience the slightest touch as painful? Why do some injured soldiers perform heroic feats and claim that they felt no pain at the time?
Nobody quite knows, but new findings by Meinhart Zenk and Toni Kutchan at the Donald Danforth Plant Science Center offer some tantalizing possibilities.
Humans and other mammals excrete morphine in their urine. That has been known for a long time. The levels of morphine are also known to vary widely. The source of the morphine has been the unanswered question until now.
Zenk and colleagues in Germany showed in a recent article that mice, and presumably all mammals, have the metabolic equipment to manufacture morphine from the amino acid tyrosine, found in all proteins. Furthermore, the way morphine is produced by mammals mimics the same chemical steps as the pathway that the opium poppy uses.