A study of selected catecholamine metabolizing enzymes: a comparison of depressive suicides and alcoholic suicides with controls

—The regional distributions of monamine oxidase (MAO) (EC 1.4.3.4), catechol-O-methyltransferase (COMT) (EC 2.1.1.6), tyrosine hydroxylase (TH) (EC 1.14.3.2), and dopamine-β-hydroxylase (DBH) (EC 1.14.2.1) have been examined in human brains obtained at autopsy from persons who died of natural causes (controls), and from persons who committed suicide and were further categorized as suffering from affective disorder (depression) or from alcoholism. Post mortem animal studies showed no changes in MAO or COMT activities in rabbit brain or in DBH activity in rat brain when the intact bodies were left at room temperature up to 24 h. TH activity in rabbit brains, however, began to decline immediately after death and after 24 h at room temperature it was approximately 48 per cent of the fresh brain level. There was no significant variation in activity of COMT, TH and DBH in human brain attributable to age or sex. MAO activities in the 60–70 yr decade were 34 per cent higher than in the 30–40 yr decade. MAO activities were highest in the hypothalamus and substantia nigra, TH activities were highest in substantia nigra, putamen and head of caudate, and DBH activities were greatest in tegmentum of pons and hypothalamus. Only minimal regional differences in COMT activities were observed. No significant differences were found between enzyme activities in brain areas of controls and suicides with the possible exception of TH in the substantia nigra, where the depressive suicides (but not the alcoholics) showed greater activity (P < 0·02). These findings appear not to support the catecholamine hypothesis of affective disorder.