Renal 131I-hippurate clearance overestimates true renal blood flow in the instrumented conscious dog.
We evaluated renal 131I-hippurate clearance (ERPFhip) as a measure of renal blood flow (RBF) in chronically instrumented conscious dogs. When adjusted for renal hippurate extraction (Ehip, 0.77 +/- 0.01) and hematocrit (Hct, 39.7 +/- 1%), calculated RBFhip (656 +/- 37 ml/min) markedly exceeded renal blood flow measured with renal artery blood flow probes (RBFprobe, 433 +/- 27 ml/min). The discrepancy could not be explained by flow probe calibration, because in vivo comparison of flow probe values with renal venous outflow showed only a slight underestimation of renal blood flow (slope 0.93, 95% confidence interval 0.89-0.97). Redistribution of hippurate from erythrocytes into renal venous plasma during or shortly after blood sampling led to an underestimation of Ehip by 4 +/- 1% and thus could only explain a small part of the difference. Extrarenal hippurate clearance was excluded, because the amount of 131I-hippurate cleared from plasma equaled that appearing in the urine (303 +/- 17 and 307 +/- 17 ml/min). Applying these corrections, we found that RBFhip still exceeded RBFprobe by 37 +/- 3%. These data indicate that renal blood flow measured by the hippurate clearance technique markedly overestimates true renal blood flow. Because other errors were excluded, a combination of sampling of nonrenal blood and intrarenal hippurate extraction from erythrocytes might play a role.
Visscher
C A
CA
Department of Medicine, Groningen Institute for Drug Studies, University Hospital, The Netherlands.
De Zeeuw
D
D
Navis
G
G
Van Zanten
A K
AK
De Jong
P E
PE
Huisman
R M
RM
D000818:Animals; D001692:Biological Transport; D002404:Catheterization; D004285:Dogs; D004910:Erythrocyte Membrane / Q000378:metabolism; D006400:Hematocrit; D006626:Hippurates / Q000097:blood*; D007457:Iodine Radioisotopes; D007668:Kidney / Q000378:metabolism*; D008297:Male; D012079:Renal Circulation; D012082:Renal Veins; D012212:Rheology; D014465:Ultrasonics
D006626:Hippurates; D007457:Iodine Radioisotopes; C030514:hippuric acid