3D Structure
Biol. Function
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Anabolism and Metabolism
Adrenal Medulla L-adrenaline is a hormone and a neurotransmitter. Such substances mostly transfer short-time impulses and therefore have to be activated and inactivated very fast and effectively. Adrenaline is synthesized in the neurones of the adrenal medulla (see Synthesis) and stored in the chromaffin granula. An activating signal, which can be induced through a low blood glucose level, triggers the release of adrenaline into the blood.
Adrenal Medulla
Two enzymes are responsible for the fast and effective degradation of adrenaline: the Catecholamine-O-methyltransferase (COMT) and the Monoaminoxidase (MAO).
Adrenaline - a Hormone

Adrenaline has the opposite effect of insuline. It is a first messenger hormone and will be released when the glucose level in blood is low. Because of the binding to the -adrenergic receptors, it triggers the adenylatcyclase cascade (or cAMP cascade). This activating cascade effects the mobilisation of glycogene (liver) and triacylglycerines (fat tissue) and a generel increase of the metabolic rate. The resulting rise in blood sugar enables the fermentation of glucose in the muscles. Adrenaline furthermore reinforces these effects, because it increases the secretion of glucagon (a hormone with the same effects as adrenaline) and decreases the release of insulin.
Adrenaline - a Neurotransmitter

Adrenaline works also as neurotransmitter and has an effect on the sympathetic nervous system (heart, lungs, blood vessels, bladder, gut and genitalia). This neurotransmitter will be realeased by nervous stimulation in response to physical or mental stress and binds to a special group of transmembrane proteins - the adrenergic receptors. There are two kinds of adrenergic receptors: the - and -receptors.
Its effects are: increase in the rate and strength of the heartbeat, dilation of bronchi and pupils, vasoconstriction, sweating and reduced clotting time of the blood. Blood is shunted from the skin and viscera to the skeletal muscles, coronary arteries, liver and brain.

L-adrenaline has only a short lifetime because of its fast degradation. The oral intake of adrenaline has no effect. Therefore it has to be administered parenterally. It is used as sympathicomimeticum (drugs, which support the beating of the heart), broncholyticum (drugs, which relax the brochial muscles) and antiasthmaticum (drugs against asthma). It also is used to staunch or prevent bleedings during surgery or in the case of inner organ bleeding. Because adrenaline leads to contraction of blood vessels, it is administered in combination with local anaesthetics. In this combination, anaesthetics have a longer lasting effect and can be administered in smaller doses.

Last change: 1999-04-12