The effect of saline infusion and hemorrhage on glomerular filtration pressure and single nephron filtration rate

Summary

Single nephron filtration rate (GFRs) and effective glomerular filtration pressure (EFP) measured as the difference between intratubular stop-flow (SFP) and free-flow pressures (FFP), were determined in control rats and following saline infusion or hemorrhage. Infusion of isotonic or 4% NaCl increased EFP and GFRs without significantly affecting TF/P inulin. These findings could not be related to changes in arterial blood pressure. Controlled bleeding produced a marked decrease in EFP and in GFRs, again without significant change in TF/P-inulin. In both infusion and hemorrhage the change in GFRs was disproportionately greater than the change in EFP. Analysis of the components of the filtration process suggests that elevation of EFP is attended by an increase in permeability of the filtering membrane. This sensitive dependence of GFRs upon EFP, combined with a demonstrated constancy of total kidney GFR (GFR_T) over a wide range of urine concentrations and flow rates, connotes a close regulation of EFP in this experimental animal.