Micropuncture Study of Pressures in Proximal and Distal Tubules and Peritubular Capillaries of the Rat Kidney During Osmotic Diuresis

Abstract

A method is described for the identification of proximal and distal tubules on the surface of the living rat kidney. In 32 anesthetized rats, under control conditions, the hydrostatic pressure in the proximal tubules averaged 12.5 ± 2.2 mm Hg and 6.7 ± 1.6 mm Hg in the distal tubules. During infusion of hypertonic solutions of mannitol, glucose, urea and sodium chloride, the lumina of the proximal and distal tubules dilated and the intratubular pressures and rate of urine flow increased. Also during diuresis, the clear-cut difference between proximal and distal intratubular pressures disappeared and, in general, there was a linear relation between distal intratubular pressure and rate of urine flow. These results are interpreted to mean that the collecting system is a limiting factor in the outflow of urine from the kidney, and is an important determinant of the intratubular pressure, particularly at high rates of urine flow.