5-hydroxytryptamine Metabolism by the Nuclear Fraction of Rat-liver Homogenate.

1. The metabolism of 5-hydroxy[1'-(14)C]tryptamine creatinine sulphate in the nuclear fraction of rat-liver homogenate was studied. In the incubation mixture five metabolites were found. 2. Two metabolites were not radioactive; one of them was identified as 5-hydroxyindole-3-carboxylic acid and the second tentatively as 5-hydroxyindole-3-aldehyde. 3. 5-Hydroxyindol-3-ylacetic acid, 1'-N-acetyl-5-hydroxytryptamine and 5-hydroxytryptophol were not precursors of 5-hydroxyindolealdehyde and 5-hydroxyindolecarboxylic acid. 4. It was shown that the metabolism of 5-hydroxytryptamine in the nuclear fraction involves monoamine oxidase, the precursor of 5-hydroxyindolealdehyde and 5-hydroxyindolecarboxylic acid being most probably 5-hydroxyindol-3-ylacetaldehyde.