1. In order to study the role of the kidney in the elimination of endogenous plasma renin, renin was measured in the plasma and urine of female mice.
2. The renin concentration was two orders of magnitude lower in urine than in plasma, but it increased after intraperitoneal injection of submandibular mouse renin. No correlation between the plasma renin concentration and the urinary renin concentration and renin excretion rate could be demonstrated.
3. Blockade of the tubular reabsorption of proteins by intraperitoneal injection of the basic amino acid lysine increased the urinary renin concentration, renin excretion rate and renin clearance two to three orders of magnitude, without affecting the plasma renin concentration.
4. This finding demonstrates that ultrafiltered renin is reabsorbed almost completely in the renal tubules and that the mechanism most likely is the same as for other filtered proteins.
5. The large renal renin clearance obtained after intraperitoneal lysine is in accordance with a major role of the kidneys in the elimination of renin from the circulation, by a glomerular ultrafiltration and tubular reabsorption and metabolization of renin.