Main Page | See live article | Alphabetical index An adrenergic receptor (or adrenoceptor) is a cell membrane protein that is the target of catecholamines. Adrenergic receptors specifically bind the catecholamines adrenaline and noradrenaline (also called epinephrine and norepinephrine) and are activated by these. Many cells possess these receptors, and the binding of an agonist will generally cause the cell to respond in a flight-fight manner. For instance, the heart will start beating quicker and the pupils will dilate. Table of contents 1 Sub-types of adrenergic receptors 1.1 Alpha-1 receptors 1.2 Alpha-2 receptors 1.3 Beta-1 receptors 1.4 Beta-2 receptors 1.5 Beta-3 receptors 2 External links Sub-types of adrenergic receptors There are several types of adrenergic receptors, but there are five main groups: Alpha-1 receptors In blood vessels these cause vasoconstriction. Blood vessels with alpha-1 receptors are present in the skin and the gastrointestinal system, and during the flight-or-fight response there is decreased blood flow to these organs. This is the reason people can appear pale when they've been frightened. Alpha-2 receptors When an agonist binds to an α2-receptor, cyclic AMP levels within the cell decrease. These are found on pre-synaptic nerve terminals. Beta-1 receptors These are present in heart tissue, and cause an increased heart rate by acting on the cardiac pacemaker cells. Many beta-blockers for treatment of angina will only affect these receptors and not the beta-2 receptors. Beta-2 receptors These are in the vessels of skeletal muscle, and cause vasodilation, which allows more blood to flow to the muscles, and reduces total peripheral resistance. These tend to work with adrenaline (epinephrine), but not noradrenaline (norepinephrine). Beta-2 receptors are also in bronchial smooth muscle, and cause bronchodilation when activated. Anti-asthma drugss, such as salbutamol (Ventolin) work by binding to β2 receptors. Non-selective beta-blocking drugs, such as propanolol (Inderal), can represent a risk to people with asthma by blocking the beta-2 receptors, causing bronchoconstriction. Beta-3 receptors Beta-3 receptors are present in adipose tissue and are thought to have a role in the regulation of lipid metabolism. External links Brief overview of functions of the beta-3 receptor This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.