Observations on the origin of renin in human urine.

Excretion of renin into urine was studied using specific assay methods in normal subjects and hospital patients. Urinary renin output and renal clearance of renin varied widely among normal subjects but remained similar over months in any one subject. Renin clearance was significantly less in normal males (range 12 to 893 ml/24 hours) than females (79 to 3,149 ml/24 hours), but no reason for this was established. In normal subjects renin excretion did not show a diurnal variation and was not directly dependent upon creatinine clearance, protein clearance, plasma renin levels, or sodium or water output. Fivefold elevations in plasma renin level induced by natriuretic therapy increased renin excretion twofold and caused renin clearance to fall to 43% of control without a change in creatinine clearance. Total protein excretion did not change with this elevation in plasma renin level. Excess renin excretion did not occur in patients with proteinuria unless plasma levels were grossly elevated. The findings suggest that renin is filtered and selectively reabsorbed. No diagnostic application is apparent. ADDITIONAL