Pair-tested renal reserve filtration capacity in kidney recipients and their donors

Subjects after kidney donation manifest an adaptive rise in GFR. In uninephrectomized rats, progressive glomerulosclerosis, which is induced by the compensatory glomerular hyperfiltration, develops. It has been assumed that testing the existence of renal reserve filtration capacity (RRFC) might be used to demonstrate such glomerular hyperfiltration in humans. In a paired way, the RRFC of 15 kidney recipients and their donors were investigated long term (4.9 +/- 0.8 (SE) yr) after surgery. Continuous infusions of (125I)iothalamate and (131I)hippuran were used to measure GFR and effective RPF (ERPF). RRFC was tested by the infusion of dopamine, amino acids, and a combined infusion of these agents. The GFR, ERPF, and RRFC of the recipients did not differ from that of their donors. RRFC had also been tested in 12 donors, before and short term (1.3 +/- 0.3 (SE) months) after the kidney donation. Thus, the RRFC of the kidney donors could be monitored longitudinally. GFR measured short term after kidney donation amounted to 62% (+/- 2.1% SE) of the value before donation and to 68% (+/- 1.7% SE; P < 0.005) of the value long term after donation. Short- and long-term ERPF both amounted to 68% of the value before donation. The RRFC tested with the amino acids of the donors before kidney donation did not differ from that either short-term or long term after donation. Likewise, the RRFC tested with the amino acids of the recipients was similar to that of the donors before kidney donation. In contrast, in kidney recipients and donors, both short and long term after donation, RRFC tested with dopamine was approximately halved compared with that of the donors before donation. It was concluded, first, that testing RRFC cannot be used to test the existence of maladaptive glomerular hyperfiltration in subjects with a single kidney: Second, GFR increases for years after kidney donation, probably because of the compensatory hypertrophy of the remaining kidney.