Medical Pharmacology Chapter 13: Pain Management: Opioids
The rationale for endogenous opioid peptides came from the idea that opioid receptors are probably present in the body for the purpose of interacting with endogenous or naturally occurring substances. As a consequence, research proceeded to attempt identification of these naturally occurring substances now known as ß-endorphins and related peptides.
Morphine (and related agents) cause analgesia by acting at the brain regions containing peptides which have opioid-like properties
Endogenous substances = endogenous opioid peptides
Previous used term "endorphin" now refers to ß-endorphins and related peptides derived from the precursor: prepro-opiomelanocortin
Most widely distributed opioid analgesic peptides:
Three major precursor proteins:
Prepro-opiomelanocortin (POMC) containing:
Some nonopioid peptides:
Preproenkephalin (proenkephalin A ) containing:
Six copies of met-enkephalin
One copy of leu-enkephalin
Preprodynorphin (proenkephalin B) containing active peptides containing the leu-enkephalin sequence.
α and β neoendorphin
Endogenous opioid precursors which are localized at pain modulation brain regions are probably released during stress, including pain or pain anticipation.
Also, precursor molecules for endogenous opioids are localized in adrenal medulla and gut neural plexuses.