Connection between the changes in tubular reabsorption and in glomerular filtration rate induced by replacement of plasma sodium and chloride by isotonic mannitol.

Glomerular filtration and tubular reabsorption have been investigated comparatively in isolated blood-perfused dog kidneys, after addition to the blood of equal volumes of isotonic sodium chloride or isotonic mannitol. In the absence of antidiuretic hormone activity, the urine output showed no significant difference, while the glomerular filtration rate was lower in the presence of the mannitol load. The inhibition of fluid reabsorption was compensated by the decrease of filtration; a quantitative tubulo-glomerular equilibrium was evidenced. The fractional sodium excretion was decreased following the dilution by the mannitol load of plasma sodium and -chloride; this difference disappeared when the reabsorption in the diluting segment was inhibited by furosemide, suggesting that it depended on the rate of chloride reabsorption in this part of the tubule.