Renal 131I-hippuran extraction in man: effects of dopamine

AimsThis study examined the 131 I-hippuran extraction fraction during baseline renal blood flow rates and at high flow rates induced by dopamine.Methods In 12 healthy subjects, arterial and renal venous sampling was used to measure the renal extraction of 131 I-hippuran.Effective renal plasma flow values determined by the urinary clearance of 131 I-hippuran were compared with renal plasma flow values corrected for incomplete extraction of 131 I-hippuran.Results Dopamine (3 m g kg -1 min -1 ) decreased 131 I-hippuran extraction from 75 ± 4% at baseline to 62 ± 6% (means ± 95% confidence intervals, P < 0.001).Hence, the increase in renal plasma flow (85 ± 23%) greatly exceeded the rise in effective renal plasma flow (51 ± 15%, P < 0.002).Conclusions Dopamine induced increases in renal blood flow are largely underestimated when measurements are not corrected for incomplete extraction of 131 I-hippuran.