Effect of sodium restriction on plasma renin activity and renin granules in rat kidney

The present study was carried out to procure detailed information on the relationship between chronic sodium restriction and renin content of kidneys at a subcellular level in the rat. Renin granules (RG) were separated by a discontinuous sucrose-density gradient (from 1.2 to 1.7 M) centrifugation. In control rats, RG were mainly recovered in the fractions corresponding to 1.5 M sucrose, whereas most of the mitochondria, lysosomes, and microsomes equilibrated in upper fractions. The RG fraction contained approximately 60% of total granular renin activity. Low sodium intake for 4 wk resulted in a 12.4-fold increase in plasma renin activity and led to a 2.6-fold increase in renin activity of the RG fraction. But in sodium-restricted rats there was no alteration in the distribution pattern of renin activity on sucrose-density gradients, indicating that there was no change in the density of RG. These results provide evidence for increased renin activity in storage granules following chronic sodium restriction.