Decreased 6-hydroxymelatonin excretion in Korsakoff's psychosis.

Mean (+/- SEM) urinary excretion rate of the major melatonin metabolite 6-hydroxymelatonin (micrograms/day) was lower in 7 (2.8 +/- 1.0) of 8 men with Korsakoff's psychosis (KP) than in 15 healthy men (11.4 +/- 1.4). Treatment with the alpha 2-noradrenergic agonist clonidine decreased daily 6-hydroxymelatonin excretion (p less than 0.02). Reduced daily excretion of 6-hydroxymelatonin in KP reflects decreased melatonin synthesis in the pineal gland, perhaps as a residual effect of lesions due to past thiamine deficiency (Wernicke's encephalopathy).