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 produc tion rate, and renal clearance of homovanillic acid (HVA) in 60 health y adult volunteers. The arterio-renal fractional extraction of HVA com bined with the renal plasma flow (Fick Principle) were used to estimat e the whole body HVA production rate and the renal plasma HVA clearanc e. The arterial HVA plasma concentration, whole body rate of HVA produ ction, and HVA plasma clearance were determined to be 54 +/- 3 nmol/l, 27 +/-2 nmol/min and 502 +/- 32 ml/min, respectively. The resting art erial HVA plasma concentration was positively correlated with aging, w ith the increased HVA concentrations in the older subjects being due t o a diminished renal HVA plasma clearance. The diminished clearance of HVA occurred in response to a decreased renal plasma flow; the fracti onal 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 i ncreases in the arterial level of HVA do not necessarily reflect an in creased rate of HVA production but may arise due to a diminished excre tion rate of HVA from the body.