Relation of pressure and flow to control of sodium reabsorption in the proximal tubule

Abstract

A theoretical analysis of the interrelationship between pressure and flow in the proximal tubule is presented and its implications for the control of proximal Na reabsorption is examined. A model was derived which integrates these hydrodynamic factors, and the behavior of the model was examined over a wide range of reduced glomerular filtration rates, utilizing an automatic computer. The results suggest that during reductions in glomerular filtration rate Na reabsorption in the proximal tubule is controlled by a negative feedback system which can account for the continued delivery of Na and water into the distal nephron. It is noteworthy that the model behaves in a stable fashion despite considerable variations in the particular physical characteristics of individual nephrons (e.g., distensibility, length of loop of Henle); this stability can also be attributed to the negative feedback characteristics of the system. The model, beyond yielding certain insights into the nature of the control of proximal Na reabsorption, also provides a framework for the incorporation of additional factors which may influence the reabsorption of Na and water.