Endogenous Opioids: Their Physiological Role and Receptors

2 Abstract: The Endogenous Opioid system includes a large number of opioid peptides that are ligands for numerous types of opioid receptors. Three distinct families of endogenous opioid peptides have been well characterized-Endorphins, Enkephalins and Dynorphins. More recently, two additional short peptides, Endomorphin-1 and Endomorphin-2 that display a high affinity and selectivity for µ opioid receptors have been identified. The Endogenous opioid peptides bind to three primary opioid receptor types that mediate analgesia, designated µ, and . Preferentially, Enkephalins interact with the receptor, Dynorphins interact with the receptor and Endorphins bind to both µ and receptors with comparable affinity.