Definition

A synthetic phenanthrene and partial agonist at the mu-opioid receptor and antagonist at the kappa-opioid receptor, with analgesic and sedative activities, and potential antidepressant activity and anti-hyperalgesic effect. Buprenorphine binds to and activates the mu-opioid receptors in the central nervous system (CNS), thereby mimicking the effects of the endogenous opiates. Binding to opioid receptors stimulates exchange of GTP for GDP, inhibits adenylate cyclase, and decreases intracellular cAMP. This inhibits the release of various nociceptive neurotransmitters, such as substance P, gamma-aminobutyric acid (GABA), dopamine, acetylcholine, noradrenaline, vasopressin, and somatostatin. In addition, buprenorphine closes N-type voltage-gated calcium channels and opens calcium-dependent inwardly rectifying potassium channels, resulting in hyperpolarization, reduced neuronal excitability, analgesia and sedation. Buprenorphine also acts as an antagonist at the kappa-opioid receptor, which may result in antidepressant activity and anti-hyperalgesic effect.