On the glomerular tubular balance in the rat kidney

1. The concept of glomerular tubular balance implies the constancy of fractional reabsorption of glomerular filtrate by the proximal convoluted tubules despite alterations in the arterial blood pressure or GFR. This concept was investigated in the kidney of the nondiuretic rat during acute alterations in arterial pressures from 50-160 mm Hg. 2. Three different methods independent of each other were used instead of the conventional approach of measuring the inulin TF/P ratios alone: a) determination of the transporting capacity of proximal tubules by the split oil droplet method; b) estimation of the passage time of fluid through the proximal convoluted tubules an c) measurement of the inulin TF/P ratios. 3. Transporting capacity of the proximal tubule was constant and independent of the arterial pressure. Proximal passage time became shorter as arterial pressure was raised from 50-160 mm Hg. Increase in GFR was followed by shortening of proximal passage time. Inulin TF/P ratios in proximal convolutions increased with longer and decreased with shorter passage times. The fractional reabsorption decreases when the arterial pressure is raised and increases when it is lowered. These results do not support the concept of the existence of glomerular tubular balance in the nephrons of nondiuretic rats during acute changes in arterial pressure.