Micropuncture Study of the Effect of Acute Reductions in Glomerular Filtration Rate on Sodium and Water Reabsorption by the Proximal Tubules of the Rat*

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Abstract
The effect of acute reductions in glomerular filtration rate on Na and water transfer by the proximal tubule was studied in rats by micropuncture methods. GFR [glomerular filtration rate] was reduced by constriction of the abdominal aorta above the origin of the renal arteries. It was found that with reductions ranging between 10 and 66%, the fraction of filtered Na and water reabsorbed by the proximal tubules remained essentially the same as under control conditions. This indicates that the absolute rate of net Na and water transfer decreased in direct proportion to the fall in GFR. Since proximal Na concentration did not change with constriction of the aorta, the decreased rate of transport was apparently the result of diminished delivery of Na to the sites of active transport. These observations support the view that proximal Na reabsorption is regulated to a large degree by flow-dependent kinetics.