Instantaneous measurement of glomerular filtration rate in the isolated perfused rat kidney

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Abstract
In perfusion studies on the isolated cellfree perfused rat kidney, the glomerular filtration rate (GFR) can be controlled if the GFR can be measured instantaneously. This paper reports on a GFR meter which opens this possibility. Vitamin B12 is used as a marker for the GFR. A bubble flow meter determines urine flow rates ranging from 10 up to 200 μl · min−1. A fiberoptic colorimeter measures vitamin B12 concentrations in the urine up to 400 mg · l−1. The flow meter and the colorimeter are described in detail. The reliability of vitamin B12 as a marker for the GFR is demonstrated and, moreover, the identity of GFR values obtained with the GFR meter and those from B12 spectrophotometry is demonstrated.