Renal clearances of 14C-inulin and polyfructosan in the rat. Effect of increased ureteral pressure.

Polyfructosan has been used as a substitute for inulin in GFR determinations. However, the validity of this substitution in conditions where renal tubular permeability to other substances, such as mannitol, sucrose and other substances, such as mannitol, sucrose and iothalamate, is increased has not been tested. Experiments were performed on 8 rats to compare the clearances of polyfructosan (CPF) and 14C-inulin (CIN) during hydropenia, 3% BW saline expansion, elevation of one ureteral catheter by 30 cm, and following return of increased ureteral pressure to the control level. No significant difference between CPF and CIN could be detected except in the kidney subjected to increased ureteral pressure. However, the magnitude of this difference--which may relate to the different molecular weights of the two compounds--was so small that we conclude that the use of CPF, as an index of GFR, is no less reliable than CIN under the conditions tested.