REVIEW OF THE LITERATURE

The metabolism o f adrenaline (A) and noradrenaline (NA) may initially begin with o-methylation by catechol-o-methyltransferase (COMT) into methyladrenaline (MA) and methylnoradrenaline (MNA) (12, 13). Part of these methylated compounds are excreted in the urine (13) and a part are further deaminated bv rrionoamiIio-oxidase (MAOI into 3-niethoxy-4-hydroxymandelic acid, or vanilmandelic acid (VMA) ( 7 ) , o r are transformed by reduction to 3-methoxy-4-hydroxyphenylglycol (MHPG) (15) and excreted in the urinc. Alternatively A and NA can be deaminated in a primary process, resulting in 3,4-dihydroxymandelic acid (DHMA) (147), a part of which is excreted in the urine but a large part is o-methylated into VMA (Fig. 1). VMA is mainly excreted unchanged in the urine, but only a very small fraction is oxidated further into vanillic acid (VA) (63, 250, 298). A few other smaller metabolites of A and NA have been demonstrated. Among the metabolites of endogenous adrena line and noradrenaline VMA predominates, being about 70 times the amount of the free A and NA excreted into the urine, and about 10 times the amount of the total MA+MNA in the urine (26, 292). Following an infusion of radioactive A o r NA into man, about 4 per cent of the total dose is excreted into the urine as free hormone, slightly more than a third as VMA, and about the same amount as combined MA+MNA (93, 147, 156, 166). The part of radioactive NA injected into the circulation or the endogenous NA released from the noradrenergic neurones is rapidly taken up bp the tissues containing the noradrenergic innervation (15, 323) and is stored for the greater part as chemically unchanged