TUBULOGLOMERULAR FEEDBACK RESPONSES TO ACUTE CONTRALATERAL NEPHRECTOMY

After unilateral nephrectomy adaptive events must occur in the remaining kidney within the first 12-14 h in anticipation of an increase in glomerular filtration rate (GFR) and eventual renal hypertrophy. Utilizing micropuncture and microperfusion techniques in the rat, we have examined tubuloglomerular feedback (TGF) and single-nephron GFR (SNGFR) responses while the late proximal tubule was microperfused [late proximal tubule flow (V(LP)] from 0 to 40 nl/min in 10 nl/min intervals at 2-4 and 12 h after contralateral nephrectomy. Urinary excretion increased, but SNGFR derived from distal collections was reduced, and early distal flow rate remained constant 2-4 h after nephrectomy. The operating point was shifted, suggesting activation of TGF. The turning point half-maximal activity (V 1/2) and slope were not statistically different when all nephron data were submitted to a curve-fitting procedure, but group mean data suggested a quantitatively lower V 1/2 and steeper slope of the TGF profile. Twelve to fourteen hours after contralateral nephrectomy, values for SNGFR at all microperfusion rates were increased, as were late proximal and early distal flow rates. The values for V 1/2 and slope of TGF were not statistically different from control values. We conclude that TGF activity and sensitivity are not suppressed at 2 and 12 h after nephrectomy. Increased urinary excretion does not require TGF alterations. Changes in TGF may be adaptive to increases in SNGFR and may not be causal to the increase in filtration rate after nephrectomy.