Effect of Change in Flow Rate Upon Renal Vascular Resistance

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Abstract
The effect of changing renal flow rate upon renal vascular resistance has been studied in 82 anesthetized dogs. Resistance decreased and then increased as a function of blood flow rate. The onset of the increase in resistance was more dependent upon flow rate than arterial pressure. These relationships were unaltered by section of renal nerves, infusion of phentolamine, infusion of phentolamine and eserine and ventilation with 20% CO2. The increase in resistance remained following decapsulation but began at lower levels of flow rate and pressure. The increase in resistance was absent during perfusion with blood when dextran was intermittently used as the perfusate, during perfusion with dextran in live or dead kidneys and during perfusion with blood in dead kidneys. Elevation of arterial pressure failed to greatly elevate the flow rate of renal lymph. These observations indicate that the increase in resistance results from active vasoconstriction initiated by some local mechanism which is independent of nerves, circulating adrenalines, CO2 tension and [H+]. The mechanism likely is activated by change in flow rate.