Factors determining electrolyte excretion and renin secretion after closure of an arteriovenous fistula in the dog.

We studied 12 pentobarbital-anesthetized dogs 8 to 21 days after surgical placement of a femoral AV fistula in order to characterize the renal response to subsequent closure and reopening of the fistula. Closure of the fistula resulted in a significant reduction in cardiac output from 3.3 +/- 0.2 L/min to 2.2 +/- 0.1 (p less than 0.001) and heart rate from 163 +/- 7 beats/min to 150 +/- 7 (p less than 0.005), whereas blood pressure did not change significantly. These changes in systemic hemodynamics were associated with significant increases in GFR, renal vascular resistance, and filtration fraction and a significant decrease in RBF. UNaV (16.4 +/- 3.8 microEq/min to 31.3 +/- 6.5), UKV (27.9 +/- 1.6 microEq/min to 47.5 +/- 3.8), and UHCO3V (6.8 +/- 1.4 mumol/min to 25.0 +/- 2.4) increased significantly (p less than 0.005), whereas UCIV was unchanged. Renal denervation blunted the renal hemodynamic and natriuretic consequences of fistula closure, but other electrolyte excretory responses paralleled those in innervated kidneys. In innervated kidneys RSR fell significantly after fistula closure; RSR was low in denervated kidneys and did not change on fistula closure. Reopening the AV fistula restored systemic hemodynamics toward initial control values but produced no further changes in renal hemodynamics or electrolyte excretion. Overall, an inverse relationship between changes in cation excretion and changes in RSR was observed in innervated kidneys. These results demonstrate involvement of the renal nerves as well as an increase in GFR in the increased cation excretion that occurs after AV fistula closure. However, persistently elevated cation excretion after the reopening of the fistula may be due to other mechanisms.