The chromaffin cells or bodies which in mammals and some other vertebrates are aggregated to form a central distinct structure of a pair of adrenal glands located just cephalad of the kidneys, are in principle highly specialized nerve endings of the post-ganglionic sympathetic nervous system.
Removal of this part from the adrenal gland is not fatal. This part in mammals, birds and reptiles, produces the catecholamines, adrenaline, (adrenine or epinephrine) and noradrenaline (noradrcnine or norepinephrine).
These hormones are secreted when adrenal glands are nervously stimulated and it is thought that separate cells release adrenaline and other cells release noradrenaline (Bard, 1961; Gorbman and Bern, 1962). In this regard two types of cells can be distinguished morphologically.
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These catechols are amino acid derivatives and probably synthesize in the cell from tyrosine amino acid by way of dihydroxy- phenylalanine and its decarboxylation product dopamine.
These are rapidly inactivated by the enzyme O-methyl transferees and possibly monoamine oxidase.
Noradrenaline hormone differs from adrenaline in that the methyl group on the nitrogen is lacking. Both of these hormones contain an asymmetric carbon atom, and both naturally occur as D isomers.
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D (—) adrenaline is about 15 times more potent than the synthetic L (+) isomer ; D (—) noradrenaline is 20 times more potent than its synthetic mirror image.
The proportion of adrenaline to noradrenaline varies from one species to another, and even within an individual from one circumstance to another.
Normally adrenaline is secreted 5 to 10 times the concentration of noradrenaline in the adrenal medulla but noradrenaline is also secreted by chromaffin tissue of sympathetic nervous system.