Influence of renal clearance on peripheral homovanillic acid measurements in healthy subjects and schizophrenic patients

In order to investigate the effect of renal clearance on plasma homovanillic acid (HVA) concentrations, we examined plasma concentration and urinary excretion of HVA and creatinine per 4 h over 24 h in eight male schizophrenic patients and eight healthy male subjects. Renal clearances of HVA and of creatinine were determined per 4 h period. No significant differences were found between groups in the total 24 h excretion of either HVA or creatinine. Although differences between groups in plasma HVA concentrations and urinary HVA excretion per 4 h did not reach statistical significance, the renal clearance of HVA was significantly lower in the patient group than in the control group. There was no difference between groups in creatinine clearance. Diurnal changes were seen in the renal clearance of HVA and creatinine in both groups. Renal HVA clearance decreased from 23.00-07.00 h, with a coincident decrease in urinary HVA excretion and an increase in plasma HVA concentration. We provide evidence that renal clearance is an important determinant of plasma HVA concentration, and should be considered when interpreting plasma HVA data.