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Endogenous analgesics: do humans have the ability to synthesise morphine?

ABSTRACT

The alkaloid compound morphine is one of the strongest known opioid analgesic compounds and has a wide range of therapeutic applications (Yaksh 1997). Morphine was first isolated from the opium poppy Papaver somniferum, where it can be found in high levels (Shukla et al 2006). Trace amounts of morphine have been found in human tissues and fluids, where it was believed to be dietary in origin, coming from the ingestion of morphine-containing plant substances. Recent findings have disputed this fact and have raised questions over whether the traces of morphine found in humans and animals are dietary or endogenously synthesised.

Biosynthetic experiments on human neuroblastoma cells have shown that carcinoma cells have the ability to synthesise morphine (Poeaknapo et al 2005). If this is translated to normal human cells then this would provide further evidence for the ability of human cells to synthesise morphine.  Furthermore, the precursors for endogenous morphine synthesis in human cell lines have also been identified as oxygen, tyramine, reticulin and thebane. It seems that humans' cells have the required substrates to produce morphine.

In summary, the evidence shows that morphine is produced endogenously in humans.  There have been several suggestions of its function or benefit to humans although knowledge in this area is not currently conclusive.  Further studies will be required to conclusively show the physiological function of endogenous morphine in human beings.

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