Micropuncture Study of Pressures in Proximal Tubules and Peritubular Capillaries of the Rat Kidney and Their Relation to Ureteral and Renal Venous Pressures

Abstract

Methods are described for direct measurement of the hydrostatic pressure in the surface tubules and capillaries of the rat kidney. In fifty-six anesthetized rats intratubular pressure averaged 13.5 ± 2.4 mm Hg. Subsequent microdissection showed that all of the 112 puncture sites so localized were in the first two-thirds of the proximal convoluted tubule. Under all conditions studied, intratubular pressure and the pressure in the peritubular capillaries were approximately the same. Intravenous injection of hypertonic dextrose solution generally produced a brief rise in intratubular and peritubular capillary pressures, which returned to their preinjection levels while the diuresis so produced continued, although at less than the maximal rate. Obstruction of the ureter of kidneys undergoing diuresis resulted in a prompt rise in intratubular pressure, which agreed closely with the simultaneously determined ureteral pressure. Elevation of the ureteral pressure with a pressure bottle had no effect on intratubular or peritubular capillary pressures until it exceeded the pre-existing intratubular and peritubular capillary pressures, and then all rose together up to a maximum intratubular pressure above which elevation of ureteral pressure resulted in no further rise in intratubular or peritubular capillary pressure. Elevation of applied ureteral pressure in kidneys with collapsed tubules and in dead animals did not increase the intratubular pressure, demonstrating that the rise in intratubular pressure produced in this manner in functioning kidneys was not simply a direct back transmission of pressure. Elevation of renal venous pressure by compression of the renal vein also had no effect on intratubular and peritubular capillary pressures until their pre-existing values were exceeded, and then all three pressures rose together.