Noradrenaline/adrenergic system

The adrenergic system is an essential regulator that increases cardiovascular and metabolic capacity during situations ofstress, exercise, and disease. Nerve cells in the central and peripheral nervous system synthesize and secrete the neurotransmitters noradrenaline and adrenaline. In the peripheral nervous system, noradrenaline and adrenaline are released from two different sites noradrenaline is the principal neurotransmitter of sympathetic neurons that innervate many organs and tissues. In contrast, adrenaline, and to a lesser degree noradrenaline, is produced and secreted from the adrenal gland into the circulation (Fig. 1). Thus, the actions of noradrenaline are mostly restricted to the sites of release from sympathetic nerves, whereas adrenaline acts as a hormone to stimulate many different cells via the blood stream. 

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). 

Metabolism of adrenaline and noradrenaline 200 Commonly used drugs acting on the adrenergic system 201... 

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... 

Noradrenaline is the main catecholamine in postganglionic sympathetic nerves and in the central nervous system it is also released from the adrenal gland together with adrenaline. Recently adrenaline has also been shown to be a transmitter in the hypothalamic region of the mammalian brain so, while the terms "noradrenergic" and "adrenergic" are presently used interchangeably, it is anticipated that they will be used with much more precision once the unique functions of adrenaline in the brain have been established. 

Adrenergic drugs are natural or synthetic compounds that either partially or completely replicate the effects of norepinephrine (noradrenaline), epinephrine (adrenaline), and dopamine, and which cause a biological response similar to the activation of the sympathetic nervous system. They are also referred to as sympathomimeties beeause they mimic the stimulation of the sympathetic nervous system. 

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. 

Data of animal experiments discussed in this chapter suggest a variety of potential pharmacological targets for the treatment of pathological anxiety (Fig. 1). As the occurrence of traumatic events is usually unpredictable, it seems more promising to interfere with consolidation than with acquisition processes. In this context, the sympatho-adrenergic and the hypothalamic-pituitary-adrenal system are of particular interest. Both noradrenaline and corticosterone/cortisol are known to facilitate memory consolidation, in par-... 

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... 

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