To the Editor.—
Investigations in rodents demonstrated that short-term neuroleptic administration results in a rapid increment in the plasma homovanillic acid (pHVA) concentration, which is believed to reflect increased brain dopamine turnover.1 Pickar et al2 failed to demonstrate this acute neuroleptic-induced increase in the pHVA concentration in a group of schizophrenic patients.2 As Pickar et al2 correctly pointed out, we have also failed to detect changes in pHVA concentrations six hours after haloperidol administration.3 However, we would like to now report that there are robust increases in pHVA concentrations 24 hours after haloperidol administration.
Patients and Methods.—
Twenty-eight schizophrenic patients who were free of oral neuroleptics for at least three weeks and depot neuroleptics for at least three months participated in the study. Patients consumed a low-monoamine diet throughout the study and were fasting and at bed rest 14 hours before pHVA sampling. The pHVA