Renal dopamine spillover rate using 3H-dopamine radiotracer technique as an index of renal dopaminergic nerve activity.

Renal and total dopamine (DA) spillover rates at rest were measured in 25 conscious rabbits with chronically implanted renal vein catheters. Renal DA spillover rate was calculated from veno-arterial difference in plasma free DA concentrations across the kidney corrected by the fractional extraction of infused 3H-DA. Plasma free DA concentrations were 11.0 +/- 2.7 pg/ml in the artery and 14.3 +/- 3.6 in the renal vein. Renal and total DA spillover rates were 0.51 +/- 0.08, 2.61 +/- 0.30 ng/min, respectively, both of which were significantly (p < 0.001) lower than the respective norepinephrine (NE) spillover rates (renal: 16.3 +/- 1.4, total: 39.6 +/- 1.7). The fractional extraction of 3H-DA across the kidney (55 +/- 3%) and the total DA clearance (285 +/- 31 ml/min) were both significantly (p < 0.05) higher than that of 3H-NE (45 +/- 3) and the total NE clearance (198 +/- 9), respectively. The ratio of renal to the total spillover rate of DA (0.23 +/- 0.05) was significantly (p < 0.05) lower than that of NE (0.41 +/- 0.04). These results demonstrate that DA is released into plasma within the kidney and suggest that the measurement of renal DA spillover rate using 3H-DA radiotracer technique is useful to detect resting renal dopaminergic nerve activity.