Adrenergic blocking agent

Adrenergic blocking agents are a class of drugs that work by inhibiting the action of the sympathetic nervous system, the part of the autonomic nervous system that the body does not control by will. When the sympathetic system is active, the body releases noradrenaline (norepinephrine) and adrenaline (epinephrine), which act on adrenergic receptors of the alpha-1, alpha-2, beta-1, beta-2 and beta-3 subtypes and produce the fight-or-flight response. That response includes constriction of many blood vessels, dilation of vessels supplying skeletal muscle or the coronary circulation, and a faster, stronger heartbeat that raises the metabolic demand on the heart. Adrenergic blocking agents treat certain diseases by occupying or blocking these receptors so that noradrenaline and adrenaline cannot activate them, which stops the body from mounting the fight-or-flight response. This entry records the class as a whole rather than any single drug, and it is a description of how the class is understood, not medical advice.