Mechanisms of the early and late response of the kidney to contralateral nephrectomy

The immediate (1 day. Dl) and late (90 days, D90) effects of unilateral nephrectomy on contralateral renal hemodynamics, and the renal handling of electrolytes and water were investigated in the whole animal. The immediate and late ability of the remnant kidney to autoregulate perfusate flow and glomerular filtration rate (GFR) was studied in the isolated perfused kidney of the rat. In the whole animal, in Dl rats as compared to controls, GFR calculated for a single kidney increased from 0.85 ±0.3 to 1.1 ±0.2 ml/min (p <0.05). In D90 rats GFR increased further and was similar to prenephrectomy GFR (1.4 ±0.5 vs. 1.7 ±0.5 ml/min, p NS). Urinary prostanoid excretion in 24 h, calculated for one kidney, increased by 50-500% in Dl rats, but returned to prenephrectomy values in D90 rats. In the isolated perfused kidney, decreasing perfusion pressure (PP) from 100 to 70mmHg did not change the renal vascular resistance (RVR) in control and D90 kidneys, but in Dl kidneys RVR decreased from 8.6 ± 1.3 to 7±1.3 mmHg/ml/min (p <0.05). In D90 kidneys RVR was significantly lower as compared to control and Dl kidneys at all perfusion pressures. Decreasing PP from 100 to 70 mmHg resulted in a significant decrease in perfusion flow in control, Dl and D90 kidneys, while with the increase in PP from 100 to 130 mm Hg the perfusion flow increased significantly in all three kidney groups. GFR was not influenced by the decrease in PP from 100 to 70 mm Hg in control and Dl kidneys, but in D90 kidneys GFR decreased from 532.7± 171.0 to 227.8±70.0pl/min (p <0.01). In Dl kidneys, GFR was similar to that of controls at all perfusion pressures, while in D90 kidneys GFR was significantly higher than control or Dl kidneys at all perfusion pressures. These results indicate that: (a) the recovery in GFR observed at 90 days after uninephrectomy is not related to renal prostanoids; (b) the early increase in GFR is due to systemic factors (an increased GFR in Dl in the whole animal, and unchanged GFR in the isolated perfused kidney); (c) the late increase in GFR is due to both systemic and intrarenal factors (an increased GFR in D90 in both. whole animal and isolated perfused kidney); (d) control, D1 and D90 isolated perfused kidneys failed to autoregulate renal perfusate flow, however, control and D1 isolated kidneys autoregulated GFR when PP was lowered from 100 to 70 mmHg, while D90 kidneys did not, and (e) the remarkable vasodilation found in D90 kidneys may potentially predispose these kidneys to pressure-related damage.