Mass fragmentography of dopamine and 6-hydroxydopamine: Application to the determination of dopamine in human brain biopsies from the caudate nucleus

Abstract A method is described for the determination of dopamine and 6-hydroxydopamine in human brain biopsies ( ca. 1 mg) using mass fragmentography of N.O-trifluoroacetyl derivatives. The sensitivity limit is 10 pg of dopamine and 20 pg of 6-hydroxydopamine. Untreated phenylketonuric patients show very low dopamine concentrations (? 1.9 ng per 100 μg of protein) in the caudate nucleus compared with control persons ( ca. ) 12 ng per 100 μg of protein). The deficiency of catecholamines in the brain, probably caused by a competitive inhibition of tyrosine 3-hydroxylase by phenylalanine, is believed to be an important factor in the pathogenesis of the neurological symptoms and of the mental retardation observed.