Studies on Renin.

We have devised a method of evaluation, in terms of Goldblatt units (GU), of the data obtained in various laboratories for the excretion of renin from canine and human kidneys. An average value of 1.3 X 10" GU/min g" normal renal tissue resulted for both dog and man. A blood pressure increase of 18—45 mm Hg was induced in normal or nephrectomized, conscious or anesthetized dogs by the continuous infusion of homologous renin at even lower rates (0.25-0.50 X 10" GU/min g" renal tissue), i.e., at 20--i0% of the rate excreted by the kidney. This suggests that renin, even at its normal rate of excretion from the kidney, participates in the maintenance of normal blood pressure. The increase of blood pressure and of concentration of renin in the dog's blood was measured at infusion rates (C) of 0.0042, 0.0083, 0.0167, 0.0333, and 0.0667 GU/min. At each rate, after a fixed period of infusion (t = 60 minutes), a constant fraction (54% of the infused renin) was retained in the circulation. From this and the results of infusion experiments carried out for 30, 60, and 120 minutes, the total amount of exogenous renin, R, present in the circulation at time t can be expressed asR = C/K (1 e~). K = 0.0232 minutes" and represents the fraction of exogenous and, presumably, also endogenous renin that is being eliminated from the circulation of the normal dog per minute. Thus, the time required for removal of 50% of the renin from the blood is tw = loge 2/K = 30 minutes.