The quantitative determination of renin in the plasma of patients with arterial hypertension.

I N PREVIOUS papers we have described the presence of vasoconstrictor and vasopressor activity in dialyzed renal and peripheral venous plasma of patients with arterial hypertension.1' 2 Plasmua from such patients caused a contraction of the rabbit aorta strip) and elevated the blood pressure of nephrectomized cats. Evidence has also been presented. that an enzyme with the characteristics of "renin" is responsible for the vaasoaetivity of the plasma and that it reacts with renin-substrate to form a product that has the properties of angiotensin.1-4 In this paper a method for the quantitative determination of renin in human plasma is described. In addition, further data are presented showing that the renin-angiotensin system is responsible for activity being assayed. The method is based on measuring the amount of the reaction product, anlgiotensin II, produced by the incubation of dialyzed plasma under standardized conditions. Reninsubstrate (angiotensinogen) is also measured because the amount of angiotensin formed by renin depends upon the amount of substrate present in*the plasma. Converting enzyme is preseint in excess in the plasma; so it is not a limiting factor.5 6 All the components for the formation of angiotensin IT are present in plasma: renin, renin-substrate, and converting enzyme.3 These are all proteins, and therefore do not pass through the dialyzing membranes. Coinsequently, by dialysis it is possible to remove