HYDROSTATIC PRESSURES IN RENAL PROXIMAL AND DISTAL CONVOLUTIONS AND IN PERITUBULAR CAPILLARIES AFTER FUROSEMIDE AND ACETACOLAMIDE IN RATS

Hydrostatic pressures were measured in proximal and distal tubules and in peritubular capillaries before and after the administration of acetazolamide and furosemide. In controls, proximal pressure averaged 11.5 mm Hg and distal pressure 4.9 mm Hg. The pressures rose after acetazolamide to 13.4 mm Hg in proximal and to 10.8 mm Hg in distal tubules. The difference between proximal and distal pressures was significant in both, controls and after acetazolamide. After furosemide the intratubular pressure increased in the proximal tubule to 32.7 mm Hg and in the distal tubule to 29.5 mm Hg, the difference being not significant. The correlation between the proximal and distal intratubular pressures and urine volume was linear and significant after both acetazolamide and furosemide. The increase of intratubular pressures relative to the urine volume is less when the renal capsula was removed. The quotient, intratubular pressure/urine volume is higher some 10 min after the injection of furosemide than subsequently. The pressure in peritubular capillaries was greater than the pressure in proximal convolutions in controls but was found to be lower than intratubular pressure after furosemide. It is assumed that the flow resistance of the loop of Henle is reduced by increasing urine volume whereas intratubular flow is hindered by a resistance at the distal end of the nephron which increases both intratubular pressures and tubular diameters. © 1969 Springer-Verlag.