The effect of reducing proximal tubular fluid delivery on the rate of filtration of single nephrons

The rate of delivery of tubular fluid from the proximal tubule (PT) is thought to reset nephron filtration rate (SNGFR). In micropuncture experiments in rats we tested this hypothesis by reducing the efflux from the PT by simultaneously “double collecting” (DC) tubular fluid from the early distal tubule (DT) and from the last convolution of the PT of the same nephrons. SNGFR measured by total collection of tubular fluid was 34±3 nl/min at the DT and 34±3 nl/min at the PT (p>0.97, n=42). The simultaneous collection from proximal and distal sampling site was performed between these two paired measurements. It yielded an average SNGFR of 40±3 nl/min (p 4 minutes. Reduction and complete interruption of the delivery of native proximal tubular fluid to the Macula Densa does not seem to influence the measurement of SNGFR. Filtration rate is not significantly different when measured within few minutes at the DT and PT of the same nephrons.