URINARY-EXCRETION OF RENIN IN THE DOG - EFFECT OF CHANGES IN PLASMA-RENIN

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Abstract
By using standard clearance and stop flow techniques, anesthetized dogs were studied to clarify the mechanism(s) of excretion of renin in urine. The clearance of renin was 0.61 .+-. 0.19 ml/min in control experiments and increased significantly to 1.26 .+-. 0.38 ml/min after furosemide. The fractional excretion of renin increased from 1.51 .+-. 0.45% during control to 3.90 .+-. 0.98% after furosemide. The rate of excretion of renin was increased 10-fold during furosemide diuresis associated with a 10-fold increase in plasma renin concentration. Extracellular fluid volume expansion also produced a diuresis but no increase in plasma renin or renin excretion. Hemorrhage produced a 3.5-fold increase in plasma renin concentration and a 200 fold increase in urinary excretion of renin. When renal artery perfusion pressure was reduced to 1 kidney, the excretion of renin in the urine from that kidney increased; there was no significant change in the excretion from the contralateral kidney. Reduction in renal artery perfusion pressure was associated with a 3-fold increase in the concentration of renin in the renal vein from the experimental kidney but an insignificant 2-fold increase in the arterial plasma renin concentration. Stop-flow studies demonstrated that renin enters the urine with the glomerular filtrate. The decreased concentration of renin in samples from the proximal tubule suggests that renin is being metabolized and/or reabsorbed in this nephron segment. In the distal nephron, there appears to be a site in which renin may be added to the tubular fluid. Renin excretion in the urine may be a complicated process. Excretion of renin in the urine is related in part to plasma renin activity but probably more importantly to the rate of production of renin in the kidney.