5-S-Cysteinyldopa and dopa in serum during treatment with 8-methoxypsoralen and UVA light.

5-S-Cysteinyldopa and dopa concentrations in serum were studied by high-performance liquid chromatography (HPLC) in patients with psoriasis treated by 8-methoxypsoralen and UVA light. A marked increase in 5-S-Cysteinyldopa was found after 3 days' treatment, although no increase in pigmentation could yet be observed. The highest concentrations of 5-S-Cysteinyldopa in serum were noted after 1 or 2 weeks' treatment. In one patient who showed no increase in serum 5-S-Cysteinyldopa treatment was unsuccessful. During PUVA treatment of 3 patients with psoriasis confined to the palms and/or soles a delayed increase in serum 5-S-Cysteinyldopa was noted after 5 weeks. This delayed response after treatment of a small area of the body is remarkable, and may indicate the formation of a systemic melanocyte stimulation factor. There was no increase in the serum dopa concentrations during PUVA treatment, and dopa analysis was of no value in assessing the activity of the melanocytes. Some unexpectedly high dopa values recorded before and during PUVA treatment may be explained by the fact that dopa originates in the nervous system or the adrenals.