An
adrenergic receptor is a
cell membrane protein, that reacts to
adrenaline and
noradrenaline (also called epinephrine and norepinephrine).
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:
In blood vessels these cause vasocontriction.
When an agonist binds to an α
2-receptor,
cyclic AMP levels within the cell decrease. These are found on pre-
synaptic nerve terminals.
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.
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.