A1receptorer

A1receptorer, or α1-adrenergic receptors, are a family of G protein–coupled receptors that mediate responses to circulating catecholamines, especially norepinephrine and epinephrine. They belong to the adrenergic receptor class and primarily signal through Gq/11 proteins to activate phospholipase C, generating inositol triphosphate and diacylglycerol, and leading to an increase in intracellular calcium. This signaling causes contraction of smooth muscle and modulation of neuron excitability in various tissues.

Three subtypes exist in humans: α1A, α1B, and α1D. They show distinct tissue distributions and physiological roles. α1A is abundant in the smooth muscle of the prostate and bladder neck. α1B is widely expressed in vascular smooth muscle and contributes to systemic vasoconstriction. α1D is found in vascular smooth muscle of certain organs and in some CNS regions. The receptors contribute to resting vascular tone and help regulate blood pressure, especially during sympathetic activation.

Endogenous ligands include norepinephrine with high affinity for α1 receptors; epinephrine also activates α1 receptors but with lower selectivity. Pharmacological manipulation uses agonists such as phenylephrine and midodrine to raise blood pressure or shrink mucosal edema, and antagonists such as prazosin, doxazosin, terazosin, and tamsulosin to treat hypertension or lower urinary tract symptoms by reducing smooth muscle tone. α1-selective drugs can cause adverse effects such as orthostatic hypotension, headaches, and nasal congestion.

Clinical relevance: α1 receptors are key targets in cardiovascular and urogenital therapy. They participate in conditions like hypertension, benign prostatic hyperplasia, and Raynaud phenomenon. They also contribute to reflex tachycardia and tissue-specific responses during drug therapy. See also: adrenergic receptors, GPCRs, norepinephrine.