Alpha-adrenergic receptors are a type of G protein-coupled receptor found on the surface of cells in various tissues throughout the body, including blood vessels, heart, lungs, prostate, bladder, and central nervous system. They are activated by the neurotransmitter norepinephrine and play an important role in the regulation of smooth muscle contraction, neurotransmitter release, and blood pressure. Alpha-adrenergic receptors are the targets of medications such as alpha blockers and alpha agonists, which can be used to treat conditions such as hypertension, benign prostatic hyperplasia, and nasal congestion.