Tubuloglomerular feedback activity after acute reductions in renal mass

Removal of one kidney results in prompt increases in urinary excretion of NaCl and water from the remaining kidney, followed rather soon thereafter by increases in glomerular filtration rate (GFR). At 12-15 h and 24 h after contralateral nephrectomy, the single nephron filtration rate (SNGFR) is increased, accompanied by parallel increases in absolute proximal tubular reabsorption, late proximal tubular and early distal tubular flow rates, suggesting that these events might be critical to the increased urinary excretion. However, micropuncture studies 2-4 h after contralateral nephrectomy demonstrate that increased SNGFR and even increased distal tubular flow rates are not requirements for augmented urinary excretion, suggesting that decreased tubular reabsorption in the most distal nephron segments causes the increase in urinary excretion. Analysis of TGF profiles by stop-flow pressure response at 2-4 h after contralateral nephrectomy have suggested suppression of TGF as assessed by a rightward shift in the turning point with increasing late proximal tubular perfusion. However, our studies have examined SNGFR responses and shown no suppression of TGF profiles but a downward shift in the operating point, suggesting activation of TGF and a modest reduction in SNGFR, determined from distal tubular collections. Although SNGFR was increased at all late proximal perfusion rates 12 h after nephrectomy, the turning point (V 1/2) was not altered. TGF profiles are not suppressed within 12 h after nephrectomy while SNGFR is increased. Suppression of TGF does not cause the increase in SNGFR after nephrectomy and TGF activity is maintained and adapts to increases in SNGFR caused by TGF-independent mechanisms.