Massive Post-Obstructive Diuresis.

BACKGROUND The purpose of presenting this case is to demonstrate the degree to which the kidney is capable of selectively excreting a massive load of sodium and water when challenged with both of these, without altering the plasma levels of other ions. CASE REPORT An 8-year-old boy was admitted in severe renal failure. Workup demonstrated a high grade obstruction of a single kidney. Following dialysis, the patient underwent surgery to correct the obstruction and he developed post-obstructive diuresis. Within one week he was receiving 34 liters of essentially 1/2 Na by IV and by mouth and was excreting 70% of his filtered load of water and 50% of his filtered load of sodium. As soon as the administered fluids and Na were cut back, the kidney responded appropriately. CONCLUSIONS While post-obstructive diuresis is a real phenomenon, very frequently it is magnified by forcing diuresis with the administration of too much water. These patients are best treated by administering fluids to equal output for two to three days and then gradually cutting back on fluid intake. If the kidney responds appropriately, then fluids can be given as the patient requests.

Identification of xanthurenic acid 8-O-beta-D-glucoside and xanthurenic acid 8-O-sulfate as human natriuretic hormones.

Hormonal regulation of salt excretion and water balance by the kidneys is well documented. Before 1961, it was widely believed that the glomerular filtration rate and the steroid hormone aldosterone controlled sodium balance in the body. In 1961, deWardener et al. [de Wardener HE, Mills IH, Clapham WF, Hayter CJ (1961) Clin Sci 21:249-258] showed that when these two variables were controlled, the kidney was still able to increase sodium excretion in response to a salt load. Several lines of evidence argued for a small-molecule signal as a definitive modulator of sodium excretion by the kidney. However, the chemical nature of the suspected natriuretic agent remained unknown. Here we report the identification and natriuretic activity of two closely related small molecules isolated from human urine, xanthurenic acid 8-O-beta-d-glucoside and xanthurenic acid 8-O-sulfate. The two compounds were partially purified by activity-guided fractionation and subsequently identified by using NMR spectroscopic analyses of enriched active fractions. Both compounds caused substantial and sustained (1- to 2-h) natriuresis in rats and no or minimal concomitant potassium excretion. We believe these compounds constitute a class of kidney hormones that also could influence sodium transport in nonkidney tissues given that these tryptophan metabolites presumably represent evolutionarily old structures.