Evidence for a prostaglandin-independent defect in chloride reabsorption in the loop of Henle as a proximal cause of Bartter's syncrome.

Maximal free-water clearance was measured in five patients with Bartter's syndrome and in five patients with the hypokalemic alkalosis of persistent psychogenic vomiting. Hypokalemic alkalosis, hyperreninemia, hyperaldosteronism and excessive renal production of prostaglandin E2 were present in the patients with both disorders. Maximal free water clearance was abnormally low, in association with a high clearance of chloride, in all the patients with Bartter's syndrome; it was normal in all the patients with psychogenic vomiting. In the patients with Bartter's syndrome, apparent distal delivery of proximal tubular fluid was inversely related to glomerular filtration rate and was excessive only in those patients with a low glomerular filtration rate. Patients with psychogenic vomiting showed mean distal fractional chloride reabsorption of 0.92 +/- 0.04 (standard error [SE]). In the patients with Bartter's syndrome, distal fractional reabsorption of chloride was 0.49 +/- 0.08 and was the same (0.46 +/- 0.06) during inhibition of prostaglandin synthesis with indomethacin therapy. Thus, a prostaglandin-independent defect in chloride reabsorption in the loop of Henle is the most proximal cause for the abnormalities in Bartter's syndrome thus far identified.