Renin and distal tubule Na during stop flow in dogs.

Using radioimmunoassay techniques, arteria (A) and renal venous (RV) plasma renin activities were measured in sodium pentobarbital-anesthetized dogs during clearance and stop-flow periods. Changes in RV-A renin were used to estimate changes in renin secretion. RV-A renin increased during stop flow from its average value during clearance periods, whether 10% mannitol in 0.15 M NaCl or 10% mannitol in 0.1 M Na2SO4 was being administered intravenously. However, RV-A renin during mannitol + NaCl stop-flow periods was significantly greater than during mannitol + Na2SO4 stop-flow periods. Distal tubular fluid Na concentrations as indicated by stop-flow analysis were higher during the latter. These observations suggest that a macula densa stimulus, Na concentration, and/or load, may control renin secretion during ureteral occlusion.