THE RENAL RESPONSE TO AN ORAL SALT AND FLUID LOAD IN CHILDREN WITH COARCTATION OF THE AORTA

The natriuretic effect of an oral salt load has been tested in 6 children before and after resection of coarctation of the aorta. Pre- and postoperative determinations of GFR and PAH clearances were also made. Preoperatively the natriuresis following the salt load was depressed, indicating enhanced tubular sodium reabsorption. The GFR was slightly elevated, the PAH clearance was normal and the filtration fraction was elevated. Postoperatively there was an increase in the natriuretic response and a fall in the filtration fraction. There was a significant inverse correlation between the filtration fraction and the urinary excretion of the salt load. The results suggest that coarctation of the aorta is associated with a shift in intrarenal vascular resistance and that this hemodynamic change will, by rise in the oncotic pressure of the peritubular capillaries, result in the enhancement of the tubular sodium reabsorption.