A STUDY OF DISTAL RENAL TUBULAR FUNCTIONS BY A MODIFIED STOP FLOW TECHNIQUE

Abstract

Stop flow studies were performed in dogs during water, NaCl, Na2SO4, and mannitol diuresis. The pelvic dead space was obliterated by the use of mineral oil, and distal convoluted tubule urine was labeled by intracortical injection of K42. As evidenced by a rise in inulin concentration in stop flow specimens, the distal convolution is highly permeable to water in the presence of vasopressin. It is quite impermeable during water diuresis. NaCl is reabsorbed in the same region. The association of permeability to water during vasopressin action and Na reabsorption serves to reduce markedly the volume of urine delivered to the collecting duct, and consequently enhances final urine osmolality. K is secreted in the area of the distal convolution and probably the collecting duct. The data suggest that previous conclusions as to K reabsorption in the distal system are erroneous, since those data were obtained in the presence of an extremely low Na concentration in the tubular fluid, and cation exchange processes were consequently limited.