Determination of bradykinin in blood by a sensitive radioimmunoassay.

Antibodies of high avidity (maximum Km 1.3 X 10(10) L/M) were produced in rabbits against bradykinin coupled to ovalbumin with toluene 2,4-disocyanate. Tyrosin8- bradykinin was labelled to a specific activity of 530-700 Ci/mmol with 125I by means of lactoperoxidase. Sensitivity of the radioimmunoassay was 0.01 microgram/l blood. Specificity studies demonstrated the essential role of the C-terminal arginine of bradykinin for binding to antibody. Mean recovery of [3H]bradykinin internal standard after the preparation of 86 blood samples was 39.0%. The major loss occurred during ethanol precipitation. In venous blood collected at random conditions from 32 normal subjects the bradykinin concentration ranged 0.04-0.46 microgram/l and showed no sex difference.