Adrenaline and Noradrenaline

Abstract

Noradrenaline and adrenaline are catecholamines that play major roles in regulation of the ‘inner world’ of the body by the brain. Noradrenaline (synonymous with norepinephrine), the main neurotransmitter of the sympathetic nervous system, is responsible for tonic and reflexive changes in cardiovascular tone. Adrenaline is a key determinant of responses to metabolic or global challenges to homeostasis, such as glucoprivation, and of manifestations of emotional distress. In contrast with the view that the sympathetic nervous and adrenomedullary hormonal systems function as a unit (the ‘sympathoadrenal system’) to maintain homeostasis in emergencies, across a variety of situations adrenaline responses are more closely linked to responses of the hypothalamic‐pituitary‐adrenocortical system than of the sympathetic nervous system. The sympathetic noradrenergic system is active even when the individual is at rest and maintains tonic levels of cardiovascular performance. Adrenoceptors in the membranes of effector cells determine the physiological and metabolic effects of catecholamines.

Key Concepts:

  • Noradrenaline and adrenaline are catecholamines.

  • Noradrenaline is the main neurotransmitter of the sympathetic nerves in the cardiovascular system.

  • Adrenaline is the main hormone secreted by the adrenal medulla.

  • The sympathetic noradrenergic system plays major roles in tonic and reflexive changes in cardiovascular tone.

  • Adrenaline is a major determinant of responses to metabolic or global challenges to homeostasis.

  • Adrenaline responses to stressors are more closely linked to responses of the hypothalamic‐pituitary‐adrenocortical system than of the sympathetic nervous system.

  • The sympathetic noradrenergic system is active even when the individual is at rest and maintains tonic levels of cardiovascular performance.

  • Adrenoceptors in the membranes of effector cells determine the physiological and metabolic effects of catecholamines.

  • Beta‐adrenoceptors mediate stimulatory effects of catecholamines on the rate and force of the heartbeat; stimulation of vascular alpha‐adrenoceptors produces vasoconstriction and increases blood pressure, and stimulation of vascular beta‐adrenoceptors – especially beta‐2 adrenoceptors in skeletal muscle – produces vasodilation.

  • Catecholamines affect cardiovascular functions by actions at adrenoceptors on cardiovascular cells, in the nervous system, and in the kidneys.

Keywords: adrenaline; epinephrine; noradrenaline; norepinephrine; catecholamine; sympathetic nervous system; stress; distress; homeostasis

Figure 1.

Diagram of steps in noradrenaline biosynthesis, release, cellular uptake and metabolism. Abbreviations: ALDH, aldehyde dehydrogenase; AR, aldose/aldehyde reductase; COMT, catechol‐O‐methyltransferase; DA, dopamine; DBH, dopamine‐beta‐hydroxylase; DHPG, dihydroxyphenylglycol; DOPA, dihydroxyphenylalanine; DOPAC, dihydroxyphenylacetic acid; DOPEGAL, dihydroxyphenylglycolaldehdye; LAAAD, l‐aromatic‐amino‐acid decarboxylase; MAO, monoamine oxidase; MHPG, methoxyhydroxyphenylglycol; NA, noradrenaline; NET, cell membrane norepinephrine transporter; NMN, normetanephrine; TH, tyrosine hydroxylase; TYR, tyrosine; and VMAT, vesicular monoamine transporter.

Figure 2.

Diagram of sources and fates of catecholamines and their metabolites in plasma. Abbreviations: AD, aldehyde dehydrogenase; ADR, adrenaline; COMT, catechol‐O‐methyltransferase; DHPG, dihydroxyphenylglycol; MAO, monoamine oxidase; MN, metanephrine; NA, noradrenaline; NMN, normetanephrine; SNS, sympathetic nervous system and VMA, vanillylmandelic acid. The black circles in white circles represent catecholamine stored in vesicles.

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Further Reading

Goldstein DS (2008) Neurochemical indices of autonomic function. In: Low P and Benarroch E (eds) Clinical Autonomic Disorders, 3rd edn, pp. 272–286. Philadelphia: Lippincott Williams & Wilkins.

Goldstein DS, Eisenhofer G and Kopin IJ (2006) Clinical catecholamine neurochemistry: a legacy of Julius Axelrod. Cellular and Molecular Neurobiology 26: 69–702.

Kvetnansky R, Aguilera G and Goldstein DS et al. (eds) (2008) Stress: Neurotransmitters, and Hormones: Neuroendocrine and Genetic Mechanisms. Boston, MA: Blackwell Publishing.

Miller AE (ed.) (2007) Autonomic Disorders. Continuum. Philadelphia: Lippincott Williams & Wilkins.

Nagatsu T, Nabashima T, McCarty R and Goldstein DS (eds) (2002) Catecholamine Research: From Molecular Insights to Clinical Medicine. New York: Plenum.

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Goldstein, David S(Sep 2010) Adrenaline and Noradrenaline. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001401.pub2]