Adrenergic receptors are a class of G protein-coupled receptors that are targets of the catecholamines. Many cells possess these receptors, and the binding of a catecholamine to the receptor will generally stimulate the sympathetic nervous system. The sympathetic nervous system is responsible for the fight-or-flight response, which includes widening the pupils of the eye, mobilizing energy, and diverting blood flow from non-essential organs to skeletal muscle. There are two main groups of adrenergic receptors, α and β, with several subtypes. α receptors have the subtypes α1 and α2. β receptors have the subtypes β1, β2 and β3. All three are linked to Gs proteins, which in turn are linked to adenylate cyclase. Agonist binding thus causes a rise in the intracellular concentration of the second messenger cAMP. Downstream effectors of cAMP include cAMP-dependent protein kinase (PKA), which mediates some of the intracellular events following hormone binding.

Norepinephrine (also known as Levarterenol or L-Noradrenaline), a neurotransmitter, is a potent adrenergic receptor (AR) agonist.

Norepinephrine is a neurotransmitter and hormone that plays a crucial role in the body’s stress response. Besides, Norepinephrine functions in the brain and body as a hormone, neurotransmitter and neuromodulator. It interacts with adrenergic receptors, mainly the β1 and β2 subtypes. The β1AR has a tenfold higher affinity for norepinephrine than the β2AR. Meanwhile, Norepinephrine has direct activity at the β2-adrenoceptor in higher concentrations. To assess the effect of Norepinephrine on cAMP production, the researchers treated the adipocytes with Norepinephrine. As expected, Norepinephrine increased cAMP production in iWA adipocytes. In addition, Norepinephrine induces lipolysis, the breakdown of fat cells, and the liberated fatty acids are required to activate UCP1 protein and stimulate heat production. Moreover, Norepinephrine increases CREB phosphorylation in iWA adipocytes.

To sum up, Norepinephrine is a neurotransmitter in both the peripheral and central nervous systems, and is potent adrenergic receptor (AR) agonist.


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[2] Xinyu Xu, et al. Cell Res. 2021 May;31(5):569-579.