2adrenergen

2adrenergen, a nonstandard term sometimes used to refer to the β-adrenergic receptor subfamily, denotes a group of adrenergic receptors that respond to the catecholamines adrenaline (epinephrine) and noradrenaline (norepinephrine). These receptors are G protein-coupled receptors that stimulate the Gs protein, increasing intracellular cyclic AMP and triggering various cellular responses.

The β-adrenergic family consists of three main subtypes: β1, β2, and β3. β1 receptors are primarily in the heart and, to a lesser extent, the kidneys, where they affect heart rate, contractility, and renin release. β2 receptors are abundant in smooth muscle and some vascular beds, including the lungs, where activation causes bronchodilation and vasodilation, and they also influence metabolic processes. β3 receptors are mainly in adipose tissue and are involved in lipolysis and energy expenditure. Receptors may be differentially expressed across tissues, and co-expression can modulate responses.

Physiological effects of β-adrenergic signaling include increased heart rate and contractility, relaxation of bronchial smooth muscle, relaxation of some vascular smooth muscle, and stimulation of lipolysis and glycogenolysis in liver and muscle. In the central nervous system, β receptors contribute to aspects of sympathetic tone and behavior.

Pharmacologically, β-adrenergic receptors are targets for agonists and antagonists. Nonselective agents affect multiple subtypes, while subtype-selective drugs are used for specific conditions. β2-selective agonists (eg, albuterol) treat asthma and COPD; β1-selective drugs (eg, metoprolol) and nonselective β-blockers address hypertension and arrhythmias. Side effects can include tachycardia, tremor, and metabolic disturbances.

See also: adrenergic receptors, alpha-adrenergic receptors, beta-blockers.