Enhanced tubular reabsorption of phosphate.

Individual kidney functions were studied during water diuresis in eight patients, following the relief of unilateral ureteral obstruction. Fractional excretion of phosphate was diminished in four of the patients, presumably due to enhanced tubular reabsorption of phosphate in the diseased side. Glomerular underperfusion may be the main factor responsible for the hypophosphaturia in the postobstructive kidney. Fractional excretion of sodium and water was increased in the obstructed side in six of the eight patients. In two of the four patients with hypophosphaturia, there was enhanced fractional sodium excretion, suggesting a dissociation of renal handling of sodium and phosphate in some patients with this condition.