Alpha2 Adrenergic Agonists

Alpha₂ and opioid receptors are found in similar regions of the brain and even on the same neurons. Both receptor types activate the same signal transduction system mediated by membrane-associated G proteins. Activation of these proteins opens potassium channels, which in turn causes the cell to lose potassium and hyperpolarize. Use of alpha₂ adrenergic agonists may be contraindicated in animals which will be adversely affected by an increase in cardiac afterload or a decrease in cardiac output. Alpha₂ adrenergic agonists increase vagal tone and may cause severe bradycardia. Duration of analgesic, sedative, and cardiovascular effects are reduced with lower doses of alpha₂ agonists. Vomiting may occur following administration, therefore their use may be contraindicated if an increase in intraocular, intracranial, intra-abdominal, or esophageal pressure will be detrimental. Alpha₂ adrenergic agonists can lead to a transient hypertension and their administration to animals with an increased potential of arterial hemorrhage may be contraindicated.