alpha2 - Adrenergic Receptors (NE)

Inhibition of adenylyl cyclase by agonists that bind to alpha2-adrenergic receptors.
Alpha2 adrenoceptor ligands inhibit adenylyl cyclase by causing dissociation of the inhibitory G protein, Gi, into its subunits; ie, an alpha_i subunit charged with GTP and a beta-gamma unit. The mechanism by which these subunits inhibit adenylyl cyclase is uncertain.
alpha2-adrenergic receptors cause specific actions in the following organs:

• Eye: ciliary epithelium (alpha-2 mediated decrease in aqueous humor production).
• Arterioles: (presynaptic alpha2-receptors cause decreased release and synthesis of catecholamines).
• Stomach and Intestine: decrease motility
• Pancreas: decreased release of insulin
• Brain (cardiovascular control center): activation of alpha2-receptors by NE causes increased parasymathetic outflow and decreased sympathetic outflow.

Adapted from Figure 9-2: StatRef Online Library: Basic and Clinical Pharmacology 8th ed. (2001)
by Michael Bolger, 8/26/01
Copyright(c) 2001 The McGraw Hill Companies, Inc. All rights reserved