[Mechanisms of the analgesic effect of alpha 2 adrenergic agonists].

Alpha 2 adrenergic agonists stimulate specific receptors in the dorsal horn of the spinal cord leading to blockade of potassium and calcium channels. Presynaptic alpha 2 receptors inhibit the release of substance P and other neuropeptides which stimulate transmission of nociceptive stimulations. Post-synaptic alpha 2 receptors hyperpolarize neurons membranes and decrease the activity of nociceptive neurons. In addition, alpha 2 adrenergic agonists have a synergistic action with opioid and cholinergic agonists.