Increase of Tryptophan and 5-Hydroxyindole Acetic Acid in the Brain of Ornithine Carbamoyltransferase Deficient Sparse-Fur Mice

Sparse-fur mice, 28 d of age with the x-chromosomal inherited defect of ornithine carbamoyltransferase, were used to investigate if tryptophan and the serotonin pathway in the brain are affected in this animal model which closely resembles the human inborn error of metabolism. Increased concentrations of tryptophan and 5-hydroxyindole acetic acid were found in forebrain and brainstem. Application of probenecid, which blocks the efflux of 5- hydroxyindole acetic acid from the brain, led to an augmented accumulation of this serotonin metabolite in the affected males. We conclude that the increased concentration of tryptophan in brain and the subsequent increased flux through the serotonin pathway are a consequence of hyperammonemia in this inherited defect of urea synthesis. Surprisingly, increased carbamoylphosphate synthetase was found in the liver of the male sparse-fur mice.