Noradrenaline/adrenergic system receptors

The biological actions of adrenaline and noradrenaline are mediated via nine different G-protein-coupled receptors, which are located in the plasma membrane of neuronal and nonneuronal target cells. These recqrtors are divided into two different groups, a-adrenergic receptors and P-adrenergic recqrtors (see P-adrenergic system). 

Noradrenaline is the neurotransmitter involved in regulating the adrenergic system it acts at a and p receptors but is most potent at a receptors. Adrenaline is a methylated metabolite of noradrenaline and functions as a circulating... 

The adrenal medulla synthesizes two catecholamine hormones, adrenaline (epinephrine) and noradrenaline (norepinephrine) (Figure 1.8). The ultimate biosynthetic precursor of both is the amino acid tyrosine. Subsequent to their synthesis, these hormones are stored in intracellular vesicles, and are released via exocytosis upon stimulation of the producer cells by neurons of the sympathetic nervous system. The catecholamine hormones induce their characteristic biological effects by binding to one of two classes of receptors, the a- and )S-adrenergic receptors. These receptors respond differently (often oppositely) to the catecholamines. 

Cardiovascular system 5-HT can directly stimulate or relax smooth muscles via 5-HTj 5-HT2 receptors and can influence the release of noradrenaline from adrenergic nerves and stimulate endothelial cells to release EDRF and prostaglandins. It... 

Sympathomimetics mimic the action of noradrenaline (norepinephrine), the principal neurotransmitter between the nerve endings of the sympathetic nervous system and the adrenergic receptors of the innervated tissues. They stimulate both alpha-adrenoceptors, causing constriction of smooth muscle and blood vessels, and beta-adrenoceptors, producing bronchodilatation. They are therefore useful in coughs where the tissues of the upper respiratory tract are congested, as they shrink swollen mucosa and open up the airways. 

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