Epsilon opioid receptor (EOR) (EOR)

The epsilon opioid receptor (EOR) is a putative G protein-coupled receptor (GPCR) within the opioid family, historically identified by its high sensitivity to the endogenous peptide beta-endorphin (Schulz et al., 1981). While the mu, delta, and kappa receptors are well-defined by specific genes, the EOR has not been definitively cloned as a separate gene product in humans and is often considered a splice variant or a specific conformational state of the mu-opioid receptor (OPRM1) (IUPHAR/BPS). Buprenorphine, a semi-synthetic opioid used in the management of severe pain and opioid use disorder, is recognized for its complex interaction with multiple opioid receptors, including partial agonism at the EOR (Huang et al., 2001). This interaction is hypothesized to contribute to buprenorphine's unique pharmacological properties, such as its high analgesic potency and its ceiling effect on respiratory depression, which enhances its safety profile compared to full mu-agonists. The EOR is involved in antinociceptive signaling and the modulation of the reward system, making it a target of interest for developing treatments that balance efficacy with reduced risk of overdose. Despite its elusive molecular identity, the EOR remains a significant concept in opioid pharmacology for explaining the diverse effects of mixed agonist-antagonist drugs like buprenorphine.

Other names

ε-opioid receptorEpsilon-type opioid receptorPutative epsilon opioid receptor

Partial agonism