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

BOSSERT, WILLIAM H., AND WILLIAM B. SCHWARTZ. Relation of pressure and flow to control of sodium reabsorption in the proximal tubule. Am. J. Physiol. 2 13(s) : 793-802. I9670 -It is the purpose of this paper to present a theoretical analysis of the interrelationship between pressure and flow in the proximal tubule and to examine its implications for the control of proximal sodium reabsorption. A model has been derived which integrates these hydrodynamic factors, and the behavior of the model has been examined over a wide range of reduced glomerular filtration rates, utilizing an automatic computer. The results suggest that during reductions in glomerular filtration rate sodium reabsorption in the proximal tubule is controlled by a negative feedback system which can account for the continued delivery of sodium 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 sodium reabsorption, also provides a framework for the incorporation of additional factors which may influence the reabsorption of sodium and water.