The alpha-1 adrenergic receptor is a G protein-coupled receptor primarily responsive to norepinephrine, found mostly postsynaptically in the central and peripheral nervous systems, and is divided into subtypes α1a, α1b, and α1d. These receptors are located in various tissues including vascular smooth muscle and play roles in functions such as vasoconstriction, mediating heart contraction, and relaxation of gastrointestinal smooth muscle. Agonists like phenylephrine are used for vasoconstriction, while antagonists like prazosin treat hypertension by inducing vasodilation.

1. Alpha-1 adrenergic receptor
Sabah Mansoor
2014-PhD-1070

2. Alpha-1 adrenergic receptor
• alpha-1 (α1) adrenergic receptor is a G protein Coupled
Receptor (GPCR) associated with the Gq, heterotrimeric
protein.
• more responsive to Norepinephrine than to epinephrine.
• Catecholamines like norepinephrine (noradrenaline) and
epinephrine (adrenaline) signal through the α1-adrenergic
receptor in the central and peripheral nervous systems.

3. Types of alpha receptors
• α-adrenoceptors exist on peripheral sympathetic nerve
terminals and are divided into two subtypes α1, and α2.
• α1 is found mostly postsynaptically, whilst α2 although
typically sited presynaptically, can also occur
postsynaptically.
• Alpha 1 adrenergic receptor consists of three highly
homologous subtypes, including α1A, α1B, α1D- adrenergic.

5. α-Adrenoceptor Location and function
Alpha 1 receptors are located on:
• all vascular smooth muscle, although densities vary
throughout the body
• GI & urinary sphincters
• dilator muscle of the iris
• arrector pili muscle of hair follicles
• On central and peripheral nervous system

6. • In the Central Nervous System they are found mostly
postsynaptically and have an excitatory function.
• Peripherally they are responsible for contraction and are
situated on vascular and on non-vascular smooth muscle.
• α1-adrenoceptors on vascular smooth muscle are located
intrasynaptically and function in response to neurotransmitter
release.
• For non-vascular smooth muscle they can be found on the
liver, where they cause hepatic glycogenolysis and potassium
release. On the heart they mediate a positive inotropic effect.
• Cause relaxation of Gastro Intestinal smooth muscle and
decrease salivary secretion.

7. Signaling Cascade

9. agonists and antigonists
Alpha 1 agonists
vasoconstrictive agents they are used to reduce edema and
inflammation. naphazoline, phenylephrine and
propylhexedrine.
Alpha 1 antagonists
causes vasodilation and decreased peripheral resistance;
therefore they are used in the treatment of hypertension
(prazosin). Treatment of benign prostatic hyperplasia.
tamsulosin is a subtype-selective alpha 1A receptor that has
more specificity toward smooth muscle in genitourinary
tract.

11. REFERENCES
• Stedeford T, Cardozo-PF, Vultaggio B, Muro CC, Luzardo GE, Harbison
RD. 2001. Alpha1-andrenergic receptors and their significance to
chemical-induced nephrotoxicity—a brief review. Res. Commun. Mol.
Pathol. Pharmacol. 110 (1-2): 59-72.
• Chen ZJ, Minneman KP. 2005. Recent progress in alpha 1-andrenergic
receptor research. Acta Pharmacol Sin. 26 (11): 1281-7.
• Piascik MT, Perez DM. 2001. Alpha1-angrenergic receptors: new
insights and directions. J. Pharmacol. Exp. Ther. 298 (2): 403-10.
• Sushmita P,Peter BR. 2011. The functional role of the alpha-1
andrenergic receptors in cerebral blood flow regulation. Indian J.
Pharmacol. 43 (5): 502-506.