The Effect of Altered Sodium Concentration in the Distal Nephron Segments on Renin Release

dium reabsorption in the ascending limb of Henle's loop, produces a sharp rise in renal venous renin activity within 5 min after intravenous administration in anes-thetized dogs. This response persists when volume de-pletion is prevented by returning urinary outflow to the femoral vein. Comparable studies with chlorothia-zide, a diuretic with little or no effect on the medullary portion of the ascending limb of the loop of Henle, failed to produce a significant increase in renal venous renin activity. When administered during ureteral occlusion, etha-crynic acid produced no change in renal venous renin activity until ureteral occlusion was released and flow restored. Following release of the ureters, a prompt rise in renal venous renin was again observed within 5 min of release. Control studies of ureteral occlusion yielded a fall in renal venous renin activity following release of the ureter without administration of ethacrynic acid. These studies identify a prompt stimulatory effect of ethacrynic acid on renin release that is unrelated to volume depletion but dependent upon the presence of tubular urine flow. Although further definition of the site and characteristics of the distal tubular mechanism for stimulation of renin release requires more direct study, the data presented here indicate that changes in sodium concentration in distal tubular fluid serve as a stimulus for renin release