Metabolism of an oral tryptophan load. II: Effect of pretreatment with the putative tryptophan pyrrolase inhibitors nicotinamide or allopurinol.
1 The effect of seven days administration of either allopurinol (300 mg daily) or nicotinamide (500 mg twice daily) on the metabolism of an oral L-tryptophan load (50 mg/kg) has been investigated. 2 Administration of either drug failed to alter the plasma total or free tryptophan or plasma kynurenine curve. Nor was the urinary excretion of tryptophan, kynurenine, 5-hydroxyindoleacetic acid or indole acetic acid influenced. 3 Allopurinol pretreatment did increase the volume of distribution of tryptophan. 4 These data suggest that allopurinol and nicotinamide are unlikely to be of value as tryptophan pyrrolase inhibitors in vivo and therefore would not increase the therapeutic effect of L-tryptophan when it is given to treat depressive illness.
D000284:Administration, Oral; D000328:Adult; D000493:Allopurinol / Q000494:pharmacology*; D006801:Humans; D008297:Male; D009536:Niacinamide / Q000494:pharmacology*; D014364:Tryptophan / Q000008:administration & dosage / Q000378:metabolism*; D014366:Tryptophan Oxygenase / Q000037:antagonists & inhibitors*
D009536:Niacinamide; D000493:Allopurinol; D014364:Tryptophan; D014366:Tryptophan Oxygenase