IDO1 and pituitary gland adenoma: Results: Serum kynurenine, kynurenic acid, 3-hydroxykynurenine, picolinic acid, IDO and kynureninase were significantly higher in the pituitary adenoma group than in healthy controls (p < 0.001), while tryptophan, kynurenine aminotransferase, anthranilic acid and quinolinic acid showed no significant differences.