Moderate increases of ureteral back pressure usually cause decreases of glomerular filtration rate and even greater decreases of sodium excretion. It has been assumed previously that increased ureteral back pressure does not enhance renal tubular sodium reabsorption directly and that the decreases of sodium excretion are caused by the decreases of glomerular filtration rate. In the experiments reported here, the effect of increased ureteral back pressure on urinary sodium excretion was studied in dogs in which changes of filtration rate were minimized by infusing saline while ureteral back-pressure was increased.
