Abstract
The aim was to study differences in filtration driving forces and glomerular filtration rates between superficial and deep nephrons when urine flow rate was altered at the macula densa region. In young rats stop-flow pressures and single nephron glomerular filtration rates (SNGFR) were measured in the superficial proximal tubules and in the loops of Henle in the papilla. SNGFR was also measured with a modified Hanssen technique. The stop-flow pressures of superficial nephrons amounted to 30.9 +/- 0.8 mmHg (mean +/- SE) and those of juxtamedullary nephrons to 52.2 +/- 1.6 mmHg. In the stop-flow condition the net driving filtration forces were calculated to be about 19 mmHg and 50 mmHg for the superficial and deep glomeruli, respectively. In free flow conditions both net driving forces were calculated to be 19 mmHg. The micropuncture technique gave a SNGFR value for superficial nephrons of 29.6 +/- 2.9 and for deep nephrons of 84.1 +/- 8.5 nl x min-1 . g-1 kidney weight (KW). With a modified Hanssen technique the corresponding values were 25.8 +/- 3.3 and 27.7 +/- 2.9 nl . min-1 . g-1 KW. The tubuloglomerular feedback mechanism is considered to have a powerful regulatory influence on the glomerular filtration rate of deep nephrons.
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