Renal handling of urate during water immersion in the nephrotic syndrome.

Renal handling of urate was examined in 11 patients with nephrotic syndrome before, during, and after 4 h of water immersion up to the neck. Urinary urate excretion, urate clearance, and fractional excretion of urate all increased significantly during water immersion, and decreased in the hour following water immersion. During water immersion fractional excretion of urate rose to a maximum of 16 ml/ml of glomerular filtrate, and fell towards control levels on removal from the bath. It is concluded that either there is a decrease in proximal tubular urate reabsorption or secretion caused by water immersion. In contrast, diurnal control studies showed no significant change in fractional excretion of urate during the same period of the day. It is postulated that the increased fractional excretion of urate on water immersion is due to hypervolemia induced by the hydrostatic pressure of the water on the lower limbs and abdomen.