Balance between tubular flow rate and net fluid reabsorption in the proximal convolution of the rat kidney. II. Reabsorptive characteristics during constriction of the renal artery

In the present study it is demonstrated that reabsorptive functions of the proximal tubule during partial renal artery clamping display significant differences when compared to spontaneous GFR variations. During moderate clamping fractional fluid reabsorption was 69.8% and fell during severe clamping to 55.2%. Proximal tubular passage time increased progressively with the degree of clamping. This indicates that radius does not change as a function of GFR, a finding supported by microphotography of the renal surface. During moderate arterial clamping proximal reabsorptive rate was correlated to the tubular cross-sectional area, but in the face of severe clamping this relationship was abolished. We conclude, therefore, that mechanisms other than tubular geometry participate in regulating proximal tubular reabsorption, when GFR is altered by arterial constriction.