Mammals catecholamines

The biological function of amine oxidases involves the oxidation of biogenic amines formed during normal biological processes. In mammals, the monoamine oxidases are involved in the control of the serotonin catecholamine ratios in the brain, which in turn influence sleep and EEG patterns, body temperature, and mental depression. Two groups of amine oxidases are involved in the oxidative deamination of naturally occurring amines as well as foreign compounds. 

THE AROMATIC FAMILY The aromatic family of amino acids includes phenylalanine, tyrosine, and tryptophan. Of these, only tyrosine is considered to be nonessential in mammals. Either phenylalanine or tyrosine is required for the synthesis of dopamine, epinephrine, and norepinephrine, an important class of biologically potent molecules referred to as the catecholamines (Special Interest Box 14.2). Tryptophan is a precursor in the synthesis of NAD+, NADP+, and the neurotransmitter serotonin. 

Humans, like most other mammals studied in the various biosciences, respond with a sympathoadrenal reaction to challenging situations. The two catecholamines, adrenaline and noradrenaline, whieh are part of this reaction, seem to have quite diOeient functions. The (peripheral) secretion of noradrenaline plays a role in the mobilization of physical resources. The seeretion of adrenaline plays a role in the mobilization of mental resources. Recently, it has become clear how adrenaline is able to do this. Peripheral adrenaline has an effect on the vagus nerve, which terrrunates in the nucleus ofthe tractus sofitarius (NTS) in the medulla NTS then sends outputs to the locus coeruleus (LC), which releases noradrenaline in widespread areas ofthe forebrain (leDoux, 1996). 

Dopamine was produced by incubating liver microsomes of rabbits with p- and m-tyramine, noradrenaline, and normetanephrine by incubation with w-octopamine, and adrenaline by incubation with p- and w-methyloctop-amine/" The injection of labelled tyramine as well as of labelled octopamine in the intact animal (rat) caused the appearance of labelled noradrenaline and normetanephrine in the urine/ As tyramine is also hydroxylated to octopamine, it is possible that the production of noradrenaline from tyramine not only takes place via its conversion to dopamine, but also via its conversion to octopamine. The possibility that octopamine is produced by the hydroxylation of tyrosine to hydroxyphenylserine with ensuing decarboxylation is under discussion. The production of noradrenaline from 3,4-dihydroxyphenylserine, 192-201) amino-acid so far not discovered in the mammal could be demonstrated both in organ extracts and in intact animals. Finally, a transamination of 3-hydroxy- or 3,4-dihydroxyphenylpyruvate to the corresponding amino-acids (m-tyrosin, dopa), and their decarboxylation to m-tyramine and dopamine was observed in intact animals (cats). For the time being it is impossible to determine the importance of the means of formation of catecholamines which have been referred to here. Of the above-mentioned precursor substances, p- and m-tyramine,( octopamine, ... 

The extensive literature about the Upolytic effect of the catecholamines< > should not be reviewed here. Our experiments show ed that epinephrine and norepinephrine at doses higher than those producing maximal effects in mammals do not elevate plasma FFA in the duck. Continuous infusion of either epinephrine or norepinephrine failed to produce fatty liver in the duck, in contrast with their effect in dogs.< ... 

The oxidation of catecholamines is catalysed by a number of enzymes which are widely distributed in the plant and animal kingdoms. The quinonoid pathway may exist as a minor but normal metabolic pathway for these substances in mammals. This question will be discussed in more detail later (see p. 318). In general, the enzymes responsible for the oxidation of the catecholamines, such as tyrosinase and ceruloplasmin, contain copper. 

Subsequent catabolism of the various catecholamines in mammals has been widely investigated and leads to a range of catechol derivatives isolable as urinary metabolites. Two enzymes, catechol-O-methyltransferase (EC 2.1.1.6) and monoamine oxidase (EC 1.4.3.4). 

Table 3. Catecholamines in the Adrenal Glands of some Adult Mammals...

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