Björn-Erik Roos

The effect of monoamine oxidase inhibitors on the level of 5-hydroxyindoleacetic acid in human cerebrospinal fluid.

Abstract IMPROVED analytical techniques have made possible the measurement of 5-hydroxyindoleacetic acid (5-HIAA) in the brain and cerebrospinal fluid. It has thus been found that rabbit brain stem contains about 0.5–0.8 μg/g. Twentyfour hours after i.v. injection of nialamid (100 mg/kg) to rabbit there is no measurable amount of 5-HIAA in the brain 1 . At the same time the 5-hydroxytryptamine (5-HT) is greatly increased. These data compare with the reports concerning inactivation of monoamine oxidase (MAO) in the brain of animals 2, 3 and humans 4, 5 . Thus Ganrot, Rosengren and Gottfries have shown that in human brain the MAO-activity after administration of clinical doses of iproniazid was less than five per cent of the normal value. Four days after the beginning of treatment with 50 mg iproniazid per day there was a decrease in MAO-activity of about 75 per cent. At the same time the values of 5-HT, noradrenaline and dopamine were about twice the normal. It was therefore possible to assume that these changes might be reflected in cerebrospinal fluid as a decrease in the level of 5-HIAA and the purpose of the investigation reported below was to test the hypothesis.