Stop-flow Pressure Research Articles

A model of glomerular ultrafiltration in the rat.

A model of glomerular ultrafiltration in the rat.

Effective glomerular filtration pressure and single nephron filtration rate during hydropenia, elevated ureteral pressure, and acute volume expansion with isotonic saline.

Free-flow and stop-flow intratubular pressures were measured in rats with an improved Gertz technique using Landis micropipets or a Kulite microtransducer. In hydropenia, average single nephron glomerular filtration rate was 29.3 nl/min, glomerular hydrostatic pressure (stop-flow pressure + plasma colloid osmotic pressure) was 70 cm H(2)O and mean glomerular effective filtration pressure was 12.7-14.3 cm H(2)O, approaching zero at the efferent end of the glomerulus. Thus, the glomerulus is extremely permeable, having a filtration coefficient four to five times greater than previously estimated. Mean effective filtration pressure and single nephron glomerular filtartion rate fell with elevated ureteral pressure and rose with volume expansion, more or less proportionately. Changes in effective filtration pressure were due primarily to increased intratubular pressure in ureteral obstruction and to reduced plasma colloid osmotic pressure in volume expansion; glomerular hydrostatic pressure remained constant in both conditions and thus played no role in regulation of filtration rate.

Pressure in the glomerular capillaries of the rat kidney and its relation to arterial blood pressure.

The pressure in the glomerular capillaries of the rat kidney was determined by micropuncture of individual nephrons. The proximal tubule was blocked by injection of viscous oil. The intratubular hydrostatic pressure increased until it reached a steady state, the intratubular stop-flow pressure. Since the glomerular capillary wall is an ultrafiltration membrane, impermeable to proteins, the sum of intratubular stop-flow pressure plus the plasma colloid osmotic pressure should equal the pressure in the glomerular capillaries. This pressure increased as the arterial pressure was raised from 60 to 90 mm Hg. Thereafter it remained constant at 88±4 mm Hg despite further elevation of the arterial pressure up to 160 mm Hg. Determination of the stop-flow pressure in Bowman's capsule and in the proximal tubules of denervated kidneys gave the same results as above.