Alpha-adrenergic receptors (AR)

Alpha-adrenergic receptors are a class of G protein-coupled receptors that are the direct molecular targets of catecholamines like norepinephrine and epinephrine. They are divided into two main subtypes, alpha-1 (α1) and alpha-2 (α2), each with further subdivisions (e.g., α1A, α1B, α1D; α2A, α2B, α2C). These receptors are widespread throughout the body and play crucial roles in regulating various physiological processes, including blood pressure, heart rate, smooth muscle contraction, and neurotransmission. Phentolamine, a pharmacological agent, acts as a non-selective antagonist, blocking both alpha-1 and alpha-2 adrenergic receptors. It is critical to distinguish between the drug (phentolamine) and its true biological targets (alpha-adrenergic receptors), as only the latter are the receptors, enzymes, or other biological molecules that drugs interact with to exert their therapeutic effects.

Other names

Alpha receptorsα-adrenoceptorsalpha adrenoceptors

Alpha-adrenergic receptors mediate their effects by coupling to G proteins. Alpha-1 adrenergic receptors (α1-AR) primarily couple to Gq proteins, leading to activation of phospholipase C, increased intracellular calcium, and subsequent effects like vasoconstriction and smooth muscle contraction. Alpha-2 adrenergic receptors (α2-AR) primarily couple to Gi/o proteins, leading to inhibition of adenylyl cyclase, decreased cAMP levels, and effects such as inhibition of neurotransmitter release and peripheral vasodilation (via central action). Drugs targeting these receptors can act as agonists (activating them) or antagonists (blocking them), thereby modulating these physiological responses.