ABSTRACTS PRESENTADOS AL 11th INTERNATIONAL SYMPOSIUM "RADIONUCLIDES IN NEPHRO-UROLOGY", REALIZADO EN MONTEREY, CALIFORNIA, 13-17 MAYO 2001.

10. EVALUATION OF RENAL FUNCTION IN RATS: RENAL CLEARANCE OF 99mTc-DTPA UNDERESTIMATES GLOMERULAR FILTRATION RATE (GFR) AS COMPARED WITH RENAL CLEARANCE OF 3H-INULIN OR 51Cr-EDTA.

Y.Shi, K.Thomsen, M.Rehling, S.S.Nielsen, L.E.Nielsen, J.Frokiaer. Department of Nuclear Medicine, Aarhus University Hospital, Aarhus, Denmark

The rat is the most commonly used experimental animal and frequently being used to examine the pathophysiology in renal disease. Thus, it is important to apply techniques where renal function is assessed accurately. A special challenge exists in chronic unilateral renal disease for accurate measurement of single kidney GFR (SKGFR). We therefore examined the possibility of developing a method where SK GFR is measured in rats from the plasma clearance of 99mTc-DTPA and the renographically determined renal split function. A detailed comparison of renal clearance (Clr) and plasma clearance (Clp) of 99mTc-DTPA with that of 51-Cr-EDTA and 3H-inulin was performed in conscious rats with permanent catheters in the carotic artery, jugular vein and the urinary bladder using the following protocols: 1) Comparison of Clr of 99mTc-DTPA with 3H-inulin using a constant infusion clearance technique with four periods (P1-P4)(n=11), 2) comparison of Clr of 99m Tc-DTPA with that of 51Cr-EDTA or 3H-inulin (n=8) 3) comparison of Clr of 51Cr-EDTA and 3H-inulin using a constant infusion clearance technique with Clp of 99mTc-DTPA using a single injection technique with plasma sampling 4 hours after injection (n=11) and 4) comparison of Clp of 51Cr-EDTA with 99mTc-DTPA using the single injection technique (n=5). The results surprisingly showed that Clr of 99mTc-DTPA consistently was significantly lower than Clr of 51Cr-EDTA (548±146 vs. 860±49 1/min/l00g (avg±std);p<0.01) and of 3H-inulin (548±146 vs. 975±135 1/min/l00g; p<0.01: Interestingly, Clr of 99mTc-DTPA was progressively reduced with time in contrast to a constant Clr of inulin (P1:693±108 vs 939±118; P2:591±94 vs 877±17, P3:594±74 vs 947±131; P4:569±78 vs 991±122). Furthermore, Clp of 99mTc-DTPA was significantly lower than Clp of 51Cr-EDTA (874±130 vs. 1092±43 1/min/100g;p<(0.01). The average clearance ratio DTPA/EDTA using constant infusion was 0.65±0.15 and 0.80± 0.15 after single injection. In conclusion, the present study shows that assessment of GFR using 99mTc-DTPA using based on Clr or Clp techniques is inaccurate. Thus it is not possible to provide SKGFR values using Clp of 99mTc-DTPA combined with renography. The apparent difference between the kinetics of EDTA and DTPA need to be further examined.