Distal pressure-flow relations during in vivo distal microperfusion in the rat

Distal convoluted tubule reabsorptive fluxes for various substances have been measured using the technique of in vivo microperfusion with quantitative sampling of the perfusate after it traverses a known length of tubule. It is unclear, a priori, whether physiologic pressures can be maintained under these sampling conditions. The present experiments were designed to monitor these pressure changes continuously by means of a microtransducer. We have found that over the range of 10-20 nL/min, during repeat sampling, the rise in pressure is 0.11 mmHg X nL-1 X min-1 (1 mmHg = 133.322 Pa) a value which is similar to 0.15 mmHg X nL-1 X min-1 obtained without sampling. This small rise in pressure over the microperfusion range supports the view that this technique does not introduce unphysiologic pressure effects. The present study also provides for the first time directly measured in vivo distal tubule pressure values over a wide flow range without changing whole kidney urine flow.