Studies on the site of renal salt loss in a patient with bartter’s syndrome

A child with growth retardation, hypokalemic alkalosis, and urinary salt losing is described. Pressor response to angiotensin II was reduced and renal biopsy showed striking hyperplasia of the juxtaglomerular apparatus. Renal tubular function was studied in the patient and in healthy control subjects during hypotonic saline diuresis. Glomerular filtration rate (GFR) was 128 ml/min/ 1.73 m² in the patient and 129 ±30 ml/min/1.73 m² in the control subjects. Fractional sodium delivery to the distal nephron, as estimated by (C_H2O + C_Na)/100 ml GFR, was 13.3 ml and 11.1 ± 3.5 ml in the patient and normal subjects, respectively. Sodium transport at the diluting segment [(C_H2O/C_H2O + C_Na) X100] was markedly impaired in the patient, 32% versus 80% ± 9.2% in the control subjects. The natriuretic effect of chlorothiazide was normal in the patient, which suggests that the reabsorptive capacity of the thiazide-sensitive segment of the distal nephron is preserved. The evidence presented suggests that the defective reabsorption of sodium in the patient is due to an impaired sodium transport in the ascending limb of Henle’s loop. The present study raises the possibility that a similar tubular defect may be responsible for the impaired renal handling of sodium that is often observed in patients with Bartter’s syndrome. Impaired transport of sodium localized in the distal nephron, that results in failure of the kidney to conserve salt adequately, is probably the primary disorder in some patients with Bartter’s syndrome.