Increase in proximal tubular fluid reabsorption by renal nerve stimulation. A split oil droplet study

The influence of renal sympathetic nerve stimulation on fluid reabsorption in the proximal tubules was studied in anaesthetized male Sprague-Dawley rats. Direct stimulation with a frequency of 2 Hz was applied, and a modification of the split oil droplet technique was used. The fluid reabsorption was determined as the half-time (t1/2) of the shrinking droplet. In the control situation t1/2 was 30.7 +/- 3.4 s. On stimulation at 2 Hz, t1/2 decreased in all nine rats studied by an average of 25 +/- 5%, to 22.4 +/- 2.6 s (P less than 0.01). The decrease in t1/2 indicates an increased rate of proximal tubular fluid reabsorption. The results support the concept that the anatomically established adrenergic innervation of renal proximal tubules participates in the direct regulation of tubular fluid reabsorption, a role which might be important in the control of the extracellular volume.