Stop-flow studies on ion and water reabsorption in the dog.

The stop-flow method has been used to study various aspects of renal tubular transport mechanisms. According to this method, aldosterone promotes the tubular reabsorption of sodium in the distal tubule. The method also indicates that the secretion of potassium, hydrogen and ammonium occurs in a very distal portion of the nephron. The substitution of anions such as ferrocyanide, sulfate and phosphate for chloride apparently increases the area of the nephron involved in the secretion of hydrogen and potassium. The stopflow experiments support other evidence that the rate of flow of urine through the loops of Henle affects the countercurrent multiplier system which, in turn, determines the ability of the kidneys to elaborate a concentrated urine.