1. The new method developed to measure renal tubular degradation of small filtered proteins in patients with normal renal function, using radio-labelled aprotinin (Trasylol) (R. Rustom, J. S. Grime, P. Maltby, H. R. Stockdale, M. Critchley, J. M. Bone. Clin Sci 1992; 83, 289–94), was evaluated in patients with chronic renal failure.

2. Aprotinin was labelled with either 99mTc (40 MBq) or 131I (0.1 MBq), and injected intravenously in nine patients, with different renal pathologies. 51Cr-EDTA clearance (corrected for height and weight) was 40 + 5.4 (range 11.2-81) ml min−1 1.73 m−2. Activity in plasma and urine was measured over 24–48 h, and chromatography on Sephadex-G-25-M was used to separate labelled aprotinin from free 99mTcO4 or 131I. Renal uptake was measured for 99mTc-labelled aprotinin only.

3. The volume of distribution was 20.2 + 2.3 litres. Chromatography showed all plasma activity as undegraded aprotinin, and urine activity only as the free labels (99mTcO4 or 131I).

4. As in patients with normal renal function, activity in the kidney appeared promptly, with 5.7 + 2.5% of the dose detected even at 5 min. Activity rose rapidly to 9.4 + 1.6% of dose after 1.5 h, then more slowly to 15.0 + 0.5% of dose at 4.5 h, and even more slowly thereafter, reaching 24.1 + 2.8% of dose at 24 h. Extra-renal uptake was again insignificant, and both 99mTcO4 and 131I appeared promptly in the urine, with similar and uniform rates of excretion over 24 h.

5. Both tubular uptake at 24 h and the rate of tubular metabolism over 24 h were lower than in the patients with normal renal function studied previously, but only the rate of tubular metabolism was directly related to the glomerular filtration rate (r = 0.75, P <0.02).

6. Correction for the reduced glomerular filtration rate yielded values for both tubular uptake (0.67 + 0.14 versus 0.32 + 0.03% of dose/ml of glomerular filtration rate, P <0.005), and tubular metabolism (0.033 + 0.07 versus 0.015 + 0.001% of dose h−1 ml−1 of glomerular filtration rate, P <0.005) that were higher by comparison with those for patients with normal renal function studied previously.

7. Fractional renal degradation of 99mTc-aprotinin (in h−1), derived from the mean rate of urinary excretion of the free isotope over a given interval, divided by the mean cumulative kidney uptake over the same interval, also fell steeply early, and then more slowly to 0.07 + 0.01 h−1 at 14.25 h (between 4.5 and 24 h).

8. It is concluded that the method described previously is also suitable in patients with chronic renal failure, allowing further research into renal disease progression.

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