Adrenoreseptorijärjestelmän

Adrenoreseptorijärjestelmä, better known as the adrenergic receptor system, consists of G‑protein‑coupled receptors that bind catecholamines such as norepinephrine and epinephrine. The system is divided into two major classes: alpha (α) and beta (β). Alpha receptors are further subdivided into α1 and α2 subtypes, while beta receptors include β1, β2 and β3. Each subtype displays distinct tissue distribution and intracellular signaling pathways.

α1 receptors are predominantly found in vascular smooth muscle, where their activation causes vasoconstriction and an increase in systemic blood pressure. α2 receptors are located mainly in presynaptic nerve terminals and other tissues such as platelets; they inhibit neurotransmitter release and modulate insulin secretion. β1 receptors are concentrated in the heart, mediating increased heart rate, contractility and conduction velocity. β2 receptors are common in bronchial and skeletal muscle, leading to bronchodilation and relaxation of smooth muscle. β3 receptors are expressed in adipose tissue and contribute to lipolysis and thermogenesis.

The adrenoreceptor system is essential for the acute “fight‑or‑flight” response, governing cardiovascular, respiratory, metabolic and neuroendocrine adjustments. Pharmacological agents that target specific subtypes—including selective β blockers, α antagonists and β agonists—are widely used in treating hypertension, arrhythmias, asthma and heart failure, illustrating the system’s clinical importance.

Understanding the subtype‑specific actions and regulation of the adrenergic receptors remains a focus of ongoing research, particularly in the context of chronic diseases where sympathetic overactivity can exacerbate pathophysiology.