Renal 131i-hippurate clearance overestimates true renal blood flow
in the instrumented conscious dog.
Visscher, C. Antoinette, Dick De Zeeuw, Gerjan Navis, Annie K. Van
Zanten, Paul E. De Jong, and Roel M. Huisman.
Department of Medicine, Division of Nephrology, and Department of
Nuclear Medicine, Groningen Institute for Drug Studies is part of the
research school Groningen Utrecht Institute for Drug Exploration,
University Hospital, Groningen, The Netherlands.
APStracts 3:0044F, 1996.
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, since in vivo comparison of flow
probe values with renal venous outflow showed only a slight
underestimation of renal blood flow (slope: 0.93, 95% CI: 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,
since the amount of 131I-hippurate cleared from plasma equalled that
appearing in the urine (303+/-17 and 307+/-17 ml/min). Applying the
above 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. Since other errors were excluded, a combination of sampling of
non-renal blood and intrarenal hippurate extraction from erythrocytes
might play a role.
Received 1 September 1995; accepted in final form 13 February
1996.
APS Manuscript Number F291-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96