Comparison of renal clearance of 99mTc-DTPA and inulin 131I-hippurate and PAH as well as creatinine clearance in Wistar-rats

Averages and standard deviations of 99mTc-DTPA and 131I-hippurate slope clearance were consecutively determined for 56 male Wistar rats, with a body-weight of 271 ± 69 g in a single investigation. Clearance of 99mTc-DTPA was 17.4 ± 3.4, that of 131I-hippurate was 34.3 ± 7.2 μl · s-1 per 100 g body weight. For 17 rats inulin and PAH clearances were determined after 3 days with the steady-state method with continuous infusion and 3-4 periods of urine collection. During the same periods endogeneous creatinine clearance was determined. 99mTc-DTPA slope clearance correlated well with inulin clearance, also the hippurate with the PAH clearance. The high values of the filtration fraction, calculated from radioisotope and chemical methods, and the low PAH extraction of 42% lead to the conclusion, that PAH and hippurate are incompletely eliminated by the rat kidney from plasma and therefore are inadequate for determining renal blood flow in rats. Creatinine clearance was 4.7 ± 1.38 μl · s-1 per 100 g body weight, much lower than that of inulin and 99mTc-DTPA. Therefore is assumed, that tubular reabsorption of creatinine occurs and creatinine clearance cannot serve for the evaluation of GFR in rats. For this, however, the clearance of 99mTc-DTPA seems well applicable in Wistar rats. (author)