Notes: L-DOPA-d3 is intended for use as an internal standard for the quantification of L-DOPA (Item No. 13248) by GC- or LC-MS. L-DOPA is a metabolic precursor of dopamine that is capable of crossing the blood-brain barrier.{17819} It is produced from L-tyrosine by tyrosine hydroxylase and metabolized by catechol-O-methyl transferase (COMT). In the brain L-DOPA is converted to dopamine. Formulations containing L-DOPA have been used in stroke recovery and in the treatment of Parkinson's disease.