- Belong to a family of membrane-bound guanine nucleotide-binding protein-coupled receptors
- Consists of three main subtypes with different actions:
Receptor
Location
Effect
Alpha-2A
Prefrontal cortex and locus coeruleus of the brain
- Suppresses neuronal firing reducing the activity of ascending noradrenergic pathways:
- Sedative and anxiolytic effects
- Directly stimulate presynaptic α2A- and α2C-adrenoceptors in the spinal cord, thereby inhibiting the firing of nociceptive neurons
- Analgesic (anti-nociceptive) effect
- Reduces sympathetic outflow (sympatholytic action):
- Reduces sympathetic tone (promotes hypotension)
- Reduces cardiac sympathetic activity (reduces heart rate, cardiac output and myocardial oxygen consumption)
- Reduces renal sympathetic activity (inhibits renin and vasopressin release, promotes diuresis)
Alpha-2B
Peripheral blood vessels
- Vasoconstriction
Alpha-2C
Striatum and hippocampus of the brain
- Unclear clinical effects
- Postulated to have anxiolytic effects