Disposition of homovanillic acid in the primate

The influence of aging on the plasma concentration and renal clearance of homovanillic acid

Using percutaneously placed arterial and venous catheters, we examined the influence of aging on the plasma concentration, whole body production rate, and renal clearance of homovanillic acid (HVA) in 60 healthy adult volunteers. The arterio-renal fractional extraction of HVA combined with the renal plasma flow (Fick Principle) were used to estimate the whole body HVA production rate and the renal plasma HVA clearance. The arterial HVA plasma concentration, whole body rate of HVA production, and HVA plasma clearance were determined to be 54 +/- 3 nmol/l, 27 +/- 2 nmol/min and 502 +/- 32 ml/min, respectively. The resting arterial HVA plasma concentration was positively correlated with aging, with the increased HVA concentrations in the older subjects being due to a diminished renal HVA plasma clearance. The diminished clearance of HVA occurred in response to a decreased renal plasma flow; the fractional extraction of HVA across the kidney remained unchanged with aging. This study emphasises the need for using age-matched control groups in neurochemical and neuropsychiatric studies, and demonstrates that increases in the arterial level of HVA do not necessarily reflect an increased rate of HVA production but may arise due to a diminished excretion rate of HVA from the body.

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.