High Urine Flow Rate Research Articles

Washout of renal countercurrent Na gradient by osmotic diuresis.

The antidiuretic hormone regulates the ability of the kidney to concentrate urine. There are two theories as to the nature of the renal concentrating mechanism: 1) the existence of an active water pump in a distal area which removes free water from the urine and 2) the existence of a countercurrent multiplier system in the renal pyramid which allows for passive movement of water out of the collecting ducts in response to an osmotic gradient. During stop flow, the kidneys are unable to alter appreciably the total osmotic pressure of urine. Measurement of Na concentrations along the length of the renal pyramid may be used as an index of the magnitude of the countercurrent gradient. Such determinations were made before and during mannitol diuresis in dogs. An osmotic gradient along the pyramids was evident in control kidneys and disappeared upon establishment of osmotic diuresis. These data suggest that high rates of urine flow through the loop of Henle may wash out the pre-existing countercurrent gradient. This accounts for the inability of the kidneys to concentrate stop flow urine. It also demonstrates that osmotic diuresis, which is generally thought of as only a proximal event, must also result from diminished distal water reabsorption due to the washout of the countercurrent gradient.

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

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.