β-adrenergic receptors

adrenergic receptors that respond particularly to epinephrine and to such blocking agents as propranolol. They are subdivided into two basic types: β₁, found in the myocardium and causing lipolysis and cardiac stimulation, and β₂, found in smooth and skeletal muscle and liver and causing bronchodilation, vasodilation, and increased presynaptic release of norepinephrine. A third type, β₃, is atypical; it is more sensitive to norepinephrine than to epinephrine, is relatively resistant to propranolol blockade, and may be involved in lipolysis regulation in adipose tissue. Called also beta or beta-adrenergic r's.