Inter- and intra-individual variability in the levels of plasma homovanillic acid in schizophrenic patients

BackgroundChanges in the levels of homovanillic acid in blood plasma (pHVA) may reflect changes which occur in the brain. In healthy individuals, this concentration of pHVA is stable over time.MethodsOver the course of one month, we studied 98 acute schizophrenic patients who had not been taking any medication but were administered neuroleptics upon hospital admission, together with 23 chronic schizophrenic patients on long-term treatment from whom medication was withdrawn. Blood samples were taken at regular intervals from each individual and the concentration of plasma homovanillic acid was measured.ResultsWe found relative stable values of pHVA with an intraclass correlation coefficient of 0.363 in acute patients and 0.638 (p < 0.0001) in chronic patients, although no differences were found in mean values (13.79 and 14.18 μg/L, respectively) or in the variation range (7.20 to 26.7 μg/L and 6.96 to 29.96 μg/L respectively). The index of individuality was calculated to be 1.36 in acute patients and 0.74 in chronic patients.ConclusionsDespite the wide range of values in the concentration of pHVA and the presence of pharmacological stimuli, we found a certain reproducibility in the levels of this dopamine metabolite. These findings are consistent with the idea that the dopaminergic activity is characterized by a constitutive value which would be under genetic control. The higher stability observed in chronic patients may reflect a weaker, age-related dopaminergic plasticity; conversely, it may indicate that a lack of plasticity in response to a pharmacological stimulus may be an indicator of poorer prognosis.