receptorsalpha1

Receptors alpha1, or alpha-1 adrenergic receptors, are a subgroup of G protein-coupled receptors that respond to norepinephrine and epinephrine. There are three subtypes: alpha-1A, alpha-1B, and alpha-1D, encoded by the genes ADRA1A, ADRA1B, and ADRA1D. They are expressed in various tissues with the highest densities in vascular smooth muscle, the iris dilator muscle, the prostatic and bladder neck smooth muscle, and certain regions of the brain. The subtypes show distinct tissue distributions, with alpha-1A prevalent in the prostate and lower urinary tract, alpha-1B in vascular smooth muscle, and alpha-1D in some vascular beds and CNS regions.

Alpha-1 receptors couple primarily to the Gq/11 family of G proteins. Activation stimulates phospholipase C, generating inositol trisphosphate and diacylglycerol, which increase intracellular calcium and activate protein kinase C. This cascade promotes smooth muscle contraction and other calcium-dependent responses.

Physiological roles include vasoconstriction and regulation of blood pressure, mydriasis, and contraction of the urethral sphincter and prostatic smooth muscle, contributing to urinary continence and bladder outlet resistance. In the CNS, they participate in arousal, attention, and modulation of sympathetic tone.

Pharmacology: alpha-1 agonists such as phenylephrine and midodrine induce vasoconstriction and are used as decongestants or to treat hypotension. Antagonists like prazosin, doxazosin, and tamsulosin relieve smooth muscle tone in the vascular system and lower urinary tract, with tamsulosin showing selectivity for alpha-1A. Adverse effects include orthostatic hypotension, dizziness, and nasal congestion. Clinically, alpha-1 receptors are targets in hypertension management and in symptoms of benign prostatic hyperplasia.