Adrenergic receptor

This response dilates pupils, increases heart rate, mobilizes energy, and diverts blood flow from non-essential organs to skeletal muscle.

The second hypothesis found support from 1906 to 1913, when Henry Hallett Dale explored the effects of adrenaline (which he called adrenine at the time), injected into animals, on blood pressure.

In June of that year, Raymond Ahlquist, Professor of Pharmacology at Medical College of Georgia, published a paper concerning adrenergic nervous transmission.

While the latter conclusion was subsequently shown to be incorrect (it is now known to be noradrenaline), his receptor nomenclature and concept of two different types of detector mechanisms for a single neurotransmitter, remains.

In 1954, he was able to incorporate his findings in a textbook, Drill's Pharmacology in Medicine,[6] and thereby promulgate the role played by α and β receptor sites in the adrenaline/noradrenaline cellular mechanism.

There are two main groups of adrenoreceptors, α and β, with 9 subtypes in total: Gi and Gs are linked to adenylyl cyclase.

Downstream effectors of cAMP include cAMP-dependent protein kinase (PKA), which mediates some of the intracellular events following hormone binding.

However, the opposite is true in the coronary arteries, where β2 response is greater than that of α1, resulting in overall dilation with increased sympathetic stimulation.

It causes vasoconstriction in many blood vessels, including those of the skin, gastrointestinal system, kidney (renal artery)[16] and brain.

[17] Other areas of smooth muscle contraction are: Actions also include glycogenolysis and gluconeogenesis from adipose tissue and liver; secretion from sweat glands and Na+ reabsorption from kidney.

β 2 adrenoceptor ( PDB : 2rh1 ​) shown binding carazolol (yellow) on its extracellular site. β 2 stimulates cells to increase energy production and utilization. The membrane the receptor is bound to in cells is shown with a gray stripe.
The mechanism of adrenoreceptors. Adrenaline or noradrenaline are receptor ligands to either α 1 , α 2 or β-adrenoreceptors. The α 1 couples to G q , which results in increased intracellular Ca 2+ and subsequent smooth muscle contraction. The α 2 , on the other hand, couples to G i , which causes a decrease in neurotransmitter release, as well as a decrease of cAMP activity resulting in smooth muscle contraction. The β receptor couples to G s and increases intracellular cAMP activity, resulting in e.g. heart muscle contraction, smooth muscle relaxation and glycogenolysis .