[en] Live kidney donation is an established form of organ donation but carries the risk of an unnecessary surgery in a normal individual for the benefit of the recipient. Despite a number of recent studies on the renal function of long-term kidney donors, little attention has been paid to the damaging effects of compensatory hyper-filtration on renal tubular cells immediately after donor nephrectomy. The present study therefore aimed to examine the immediate changes in renal function of the remaining kidney using a sheep model of unilateral nephrectomy. We used the gamma camera-based method to measure the glomerular filtration rate and the tubular excretion values after simultaneous injection of ^99mTc-diethylene triamine pentaacetic acid and ¹³¹I-ortho-iodohippurate tracers. Compared were the differences in the functions between the remaining left kidney immediately after clamping the right renal pedicle and the baseline values that were measured one week before unilateral nephrectomy. After radionuclide data acquisition was completed, the right kidney was removed. The mean glomerular filtration rate (GFR) increased by 52.3% from the baseline values (29.5±2.7 to 45.0±6.7 ml/min; n=40, p<0.001), while the mean effective renal plasma flow (ERPF) increased by 40% (225.5±27.8 to 357.8±38.94 ml/min; p<0.001), respectively. Mean filtration fraction was increased from 0.117 to 0.127 immediately after nephrectomy (p<0.001). We conclude that after unilateral nephrectomy the remaining kidney immediately compensates for the loss of a donated kidney by increasing glomerular filtration rate and effective renal plasma flow. (author)