COMPARATIVE-STUDY OF 2 TESTS OF RENAL DILUTING ABILITY IN BARTTERS-SYNDROME

1. Different results concerning distal NaCl reabsorption have been rep orted for patients with Bartter's syndrome in tests of renal diluting ability. We describe clearance studies performed on 3 patients with Ba rtter's syndrome using different routes for body fluid content expansi on: water was given orally and 0.45% NaCl solution intravenously. The impact of fluid composition was evaluated in one patient who additiona lly underwent a ''reverse test'': i.e., intravenous 5% glucose in wate r and an oral load of 0.45% NaCl solution. 2. Urine flow per ml glomer ular filtration rate (GFR) reached higher levels when the iv route was used (20.6 +/- 1.8 vs 11.8 +/- 5.7%, P<0.05). Fractional excretion of Na+, Cl- and osmoles increased during NaCl infusion but not during th e oral load. Also, distal delivery of solute increased and was greater than that observed in the oral test (21.9 +/- 5.5 vs 11.4 +/- 2.1%, P <0.05). 3. In contrast, fractional distal chloride reabsorption in the iv test reached subnormal values which were lower than in the oral lo ad test (65.0 +/- 11.2 vs 86.8 +/- 11.0%, P<0.05). A positive correlat ion was observed between distal delivery and Cl- fractional excretion (r = 0.87; P<0.005). In one patient, the 5% glucose infusion resulted in greater urine flow and distal delivery when compared to distilled w ater or 0.45% NaCl taken orally (28.1 vs 13.3 ml/min and 27.3 vs 12.8% , respectively). These values were as high as those observed during iv administration of hypotonic saline. 4. The iv route was always associ ated with lower rates of fractional distal chloride reabsorption (70.7 vs 89.1%) regardless of the solute composition and should be recommen ded when testing the renal diluting ability of patients suspected of B artter's syndrome.