Salt Sensitivity of tubuloglomerular feedback in subtotal nephrectomy

We found atypical tubuloglomerular feedback (TGF) responses in rats after subtotal nephrectomy (STN). Presently, we examined this phenomenon for salt sensitivity and efficiency of salt balance. To this end, micropuncture and chronic salt balance studies were performed. Rats were begun on low (commercial) or high (1% NaCl in drinking water) salt diets and underwent micropuncture after 7 days. SNGFR and tubular stop flow pressure (P SF ) were measured to characterize the TGF response. Salt intake had no impact on GFR, but sham rats had a 2‐fold higher GFR compared to STN (p=0.004). SNGFR and P SF responses to TGF activation in shams and low salt STN were typical (Fig. 1). But, in high salt STN, SNGFR responses were frankly anomalous while P SF responses were nil (*p<0.001). To examine the effect of anomalous TGF on Na balance, rats were placed in metabolic cages on normal salt for 1 week and then switched to high salt diet. Daily Na intake, output, and urine volumes were significantly higher in STN‐high salt than other groups (p<0.001). The delta Na between intake and output was significantly lower in STN‐high salt compared to shams‐high salt (p<0.001). TGF responses in STN are salt sensitive and frankly abnormal on a high salt diet. In spite of half the GFR, STN rats on a high salt diet were more efficient in excreting higher salt loads compared to shams. To facilitate salt balance, the remnant kidney sacrifices stability of distal delivery by converting TGF from negative to positive feedback.