Adrenergic receptor

Many cells possess these receptors, and the binding of an agonist[?] will generally cause the cell to respond in a flight-fright type way. For instance the heart will start beating quicker and the pupil will dilate.

There are several types of adrenergic receptors, but there are four main groups:

Alpha-1 receptors In blood vessels these cause vasocontriction.

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. A good beta-blocker 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, but not noradrenaline.