Lumbar cerebrospinal fluid homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5HIAA), and probenecid were measured in groups of patients suffering from schizophrenia or affective disorder following administration of probenecid (100 mg/kg over 18 hours) to block acid monoamine metabolite egress from cerebrospinal fluid (CSF). The CSF HVA value was lower in the total schizophrenic group compared with that of the affective disorder group and in a poor prognosis group of schizophrenics compared with that in a good prognosis group. These differences could not be accounted for by differences in CSF probenecid. Comparable net increases in HVA were produced by antipsychotic drug administration in subgroups from the two groups of schizophrenics.
If clinical schizophrenia is characterized by increased central dopaminergic transmission, this increased transmission is not associated with increased central HVA formation, as determined by the measurement of lumbar CSF HVA following probenecid.