Bartter's syndrome with a salt reabsorption defect in the cortical part of Henle's loop

The pathogenesis of Bartter's syndrome remains uncertain. The prevailing theory postulates a defect in salt reabsorption, more frequently described in the thick ascending limb of Henle's loop. The patient we studied presents a normal urinary concentration capacity associated with impaired dilution, a free water clearance at the lower end of normal (5.4 ml/min/100 ml glomerular filtrate), a decreased distal fractional chloride reabsorption (54%) when studied during hypotonic saline diuresis, and a normal decrease in free water clearance after furosemide (2.1 ml/min/100 ml glomerular filtrate), suggesting a defect in the cortical part of Henle's loop. When studied during oral water diuresis, the fractional chloride reabsorption was normal (82%). This could be explained by a relative inability of the cortical diluting segment to reach maximal absorptive rates for NaCl. An inappropriate kaliuria related to an excessive delivery of salt load to the distal tubule is suggested by the correlation between urinary potassium and chloride excretion (r = 0.84; p less than 0.001). Aldosterone secretion participates also partially in the urinary potassium loss.