Application of radioimmunoassay to the renin-angiotensin system and to aldosterone

Abstract

Many of the factors regulating the renin-angiotensin system have been defined by means of a bioassay method based on the hypertensive effect, in the nephrectomized rat, of angiotensin II generated by the action of renin on its plasma substrate. The bioassay has now been largely replaced by a simpler and more sensitive radioimmunoassay based on the generation of angiotensin I in the same system. The radioimmunoassay of aldosterone in plasma has been possible using antisera developed to aldosterone-albumin conjugates. Cross-reactivity to other steroids is low, but their greater abundance in plasma necessitates chromatographic purification before the immunoassay step. The radioimmunoassay of aldosterone in plasma is simpler and more sensitive than measurement by double isotopic techniques. Simultaneous measurement of renin activity and aldosterone in plasma, now possible by radioimmunoassay, should provide a more precise definition of the interrelationship of the two hormonal systems.