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"It is well known that unilateral nephrectomy induces a series of morphological changes in the remaining kidney. These morphological changes called as "compensatory hypertrophy and hyperplasia" are associated with numerous functional changes of the remnant kidney, such as relative increase in the glomerular filtration rate and the renal plasma flow as well as changes in the renal concentrating ability. However, changes in the water and electrolytes excretion following unilateral nephrectomy have not been extensively studied. Hence, this investigation was undertaken to study the excretory pattern of water and electrolytes through the remaining kidney following unilateral nephrectomy. Experiments were carried out in 23 hydropenic dogs, weighing 10~16 kg, of which 5 dogs were used for acute experiments (4 hrs. after nephrectomy) and 18 dogs for chronic experiments (2 weeks, 4 weeks and 6 weeks after nephrectomy). Following intravenous administration of appropriate amounts of inulin and PAH, plasma and urine samples were obtained and were analyzed for the concentration of inulin, PAH, osmolarity, Na, K and urea. In chronic experiments, Animals were allowed to have free access to the food and water during intervals. Four slices of the tissue from papilla to cortex were cut for each kidney. The Na, K, Cl and urea concentrations of the slice were then determined in slice extracts. Also four slices of the kidney cortex were obtained and analyzed for concentration of PAH. Results may be briefly summarized as follows. 1. After unilateral nephrectomy, the weight of the remaining kidney increased about 30 percent in 2-6 Weeks. 2. During 1 hours after unilateral nephrectomy, the glomerular filtration rate (GFR) of the remaining kidney showed no significant changes while the renal plasma flow (RPF) decreased gradually to a level below the control. In chronic experiments, the GFR showed no change after the nephrectomy whereas the RPF showed a 20 percent increased, thus reducing the filtration fraction. 3. During 1 hours after unilateral nephrectomy, the urine osmolarity revealed no significant changes while the fractional excretion of the filtered osmotic substance, water, sodium and potassium were gradually increased, indicating relative impairments of the tubular reabsorption of these substances. 4. During 2.-,6 weeks after unilateral nephrectomy, the renal concentrating ability of the remaining kidney was significantly impaired. The fractional excretion of the filtered water was most markedly increased while the tubular reabsorption of urea was somewhat increased. 4. No significant changes in plasma composition was noted in all animals, indicating that the overall homeostatic mechanism is apparently well maintained even after unilateral nephrectomy, 6. PAH concentration in the slices of renal cortex after unilateral nephrectomy were markedly increased, suggesting that the increase of PAH uptake on the renal cortex is partially attributable to a increase of the tubular mass of remaining kidney. 7. Medullary and papillary Na and Cl concentration was somewhat lower in the chronic experiments, indicating that the renal concenting operation is impaired in unilateral nephrectomized kidney primarily because of corresponding reduction in the medullary osmotic gradient. However, total papillary osmotic concentration at a given urine osmolarity was no significantly changed in before and after unilateral nephrectomy."
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