Control of renal factors in plasma homovanillic acid measurements

To identify and control renal factors affecting plasma homovanillic acid (HVA), a dopamine metabolite and an indicator of brain dopamine activity in clinical research, nine healthy subjects were studied on 5 nonconsecutive days. First study day was the baseline and on the other days base, salt, water, or probenecid loads were given. On each day serial concentrations of HVA and serotonin metabolite 5-hyroxyindoleacetic acid (HIAA), another organic anion, in plasma were measured. Results suggested that base, salt, and water loads did not affect plasma concentrations of either metabolite. Probenecid, which partially blocks renal organic anion transport, induced similar increases in plasma HVA and HIAA. When plasma HVA:HIAA ratio was used to control for the effect of probenecid, differences between baseline and probenecid days were no longer significant. Results suggest that HVA and HIAA are similarly handled by the kidney and that simultaneously measured plasma HIAA could be used to distinguish renal influences in plasma HVA studies.