DETERMINATION OF THE L-DOPA L-TYROSINE RATIO IN HUMAN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY - USEFULNESS AS A MARKER IN METASTATIC MALIGNANT-MELANOMA/

A first procedure was devised for determining 3,4-dihydroxyphenylalani ne (L-DOPA) in human plasma by isocratic RP-HPLC coupled with electroc hemical detection. A second procedure was devised for determining 3-hy droxyphenylalanine (L-tyrosine) in human plasma by isocratic RP-HPLC c oupled with fluorescence detection. These methods were used to ascerta in the L-DOPA/L-tyrosine ratio in plasma of patients with melanoma. Re ference values were established by analysis of the L-DOPA/L-tyrosine r atio in the plasma of 35 normal healthy subjects. For 29 patients diag nosed as having melanoma without metastasis, the L-DOPA/L-tyrosine (11 .96x10(-5)+/-2.69x10(-5)) level was not significantly different from t hat of 35 normal controls (11.20x10(-5)+/-2.92x10(-5)). However, this level was significantly increased (p<0.05) in the plasma of 17 patient s with developing metastasis (21.02x10(-5)+/-4.68x10(-5)). (C) 1997 El sevier Science B.V.