Table 1.
Receptor | Endogenous Peptides | Opioid Agonists | Effects | Side Effects |
---|---|---|---|---|
µ mu [MOR]/Oprm1 | β-Endorphins Endomorphin-1 Endomorphin-2 |
Morphine Fentanyl Meperdine Methadone Codeine Oxymorphone Hydromorphone Levorphanol |
Analgesia | Tolerance and dependence after chronic exposure to opioid
agonists Respiratory depression Nausea Urinary retention Biliary spasms and constipation Sedation Reward/euphoria |
K kappa [KOR]/Oprk1 | Dynorphin-A Dynorphin-B |
Morphine Levorphanol |
Analgesia | Tolerance and dependence after chronic exposure to opioid
agonists Diuretic effect Sedative effect Dysphoria |
δ delta [DOR]/Oprd1 | Leu-enkephalin Met-enkephalin |
Meperidine Codeine Hydromorphone Levorphanol |
Analgesia Spinal analgesia |
Tolerance and dependence after chronic exposure to opioid
agonists Antidepressant effect Reward/Euphoria Respiratory depression Constipation |
NOP | N/OFQ | — | Analgesia (spinally) | Exacerbation of chronic pain condition Tolerance to morphine Depression Hyperalgesia (low dose of N/OFQ) Parkinson’s disease |