Kinetic Measurements of the Turnover Rates of Phenylethylamine and Tryptamine In Vivo in the Rat Brain

The turnover rates of phenylethylamine and tryptamine have been estimated as their rates of accumulation after inhibition of monoamine oxidase by pargyline and were found to be 1.53 nmol/g/h and 0.24 nmol/g/h, respectively. Rate constants for the substrate activities of these amines towards monoamine oxidase were calculated as 100 h−1 and 150 h−1, respectively. Tryptamine was found to exhibit a biphasic response to increasing pargyline dosage, demonstrating its dual activity to type B and type A monoamine oxidase, for which two rate constants were obtained, kB=100 h−1 and kA=50 h−1.