Adrenergic receptors, nonselective

Class

Nonselective adrenergic agonist (OTC inhaled epinephrine)

Pathway

Adrenergic receptor signaling — beta-2-mediated bronchial smooth muscle relaxation

Notes

original target text: Adrenergic receptors, nonselective (alpha-1, alpha-2, beta-1, beta-2, beta-3); bronchodilation mediated via beta-2

Adrenergic receptors are a family of cell-surface proteins that respond to the body's own signaling molecules epinephrine and norepinephrine, part of the sympathetic nervous system that governs the 'fight-or-flight' response. The family includes several subtypes—alpha-1, alpha-2, beta-1, beta-2, and beta-3—distributed across different tissues: blood vessels, the heart, the lungs, and smooth muscle elsewhere. A nonselective adrenergic agonist activates all of these subtypes simultaneously, rather than targeting just one. In the context of respiratory disease, the therapeutically desired effect is stimulation of beta-2 receptors on bronchial smooth muscle, which causes the muscle to relax and the airway to widen, easing breathing during bronchospasm, as occurs in asthma. Because the agonist is nonselective, it also engages alpha-1 receptors (vasoconstriction), beta-1 receptors (increased heart rate and cardiac output), and other subtypes throughout the body, producing effects well beyond the lungs. This mechanism represents an older, broader approach to bronchodilation compared with agents engineered for beta-2 selectivity, and it broadly matters in any condition characterized by reversible airway constriction, while its lack of selectivity is central to understanding both its rapid onset of action and its systemic side-effect profile.