(1)
Department of Anaesthesia, Royal Free Hospital, London, UK
An opioid is a substance that shows affinity for opioid receptor. Though they are very effective in the management of pain, they may not be effective in all kinds of pain.
16.1 Receptors
The opioid receptors are widely distributed throughout the body and are synthesised in the dorsal root ganglion. The receptors are G-protein receptors and cAMP is the second messenger:
δ (OP1): weak analgesic and causes complications like seizures and is anxiolytic.
κ (OP2): poor analgesic and causes complications like catatonia, hallucinations and hyperthermia.
μ (OP3): responsible for analgesia and causes side effects like respiratory depression and constipation.
Opioid-like receptor (OP4): blocks analgesia and is anxiolytic.
16.2 Endogenous Opioids
The main precursors are proenkephalin, prodynorphin and pro-opiomelanocortin. They are cleaved by aminopeptidases, dipeptidyl carboxypeptidase and neutral endopeptidase (peptidase inhibitors).
Related posts:
Full access? Get Clinical Tree
