This paper describes a RIA for determination of the vasoactive peptide BB 30-43 and related peptides derived from leukocyte elastase degradaticn of human fibrin(ogen). The peptide was synthesized and could easily be labelled with 125I.Rabbits were iirmunized with BB 30-43 conjugated to bovine albumin. The antibody was found to bind about 5C% of the tracer in absence of BB 30-43 in a ˜1/800 diluticn. The RIA can detect peptide concentrations between 50 - 25000 pmol/L. The crossreaction with fibrinogen is very low (<0.001%) and with plas-min derived fibrin(ogen) peptides Bβ 1-42 and BB 15-42 also low (<0.2%). Plasma samples can be analyzed without any pretreatment. In an in vitro study fibrin and fibrincgen was degraded with plasmin or leukocyte elastase. Plasmin degradaticn of fibrin and fibrincgen did not release peptides which cross-reacted with our antibody, whereas leukocyte elastase degradation released peptides from both fibrin and fibrinogen which crossreact whith the antibody.The imnunolqgical activity was not changed after degrading peptide Bβ 30-43 with a) trypsin, b) plasmin, c) batraxobin, d) thrombin, e) elastase, at +37°,1 h, in a molar ratio of 1:100. Even degradaticn by elastase (1:3.5) +37°, 1 h, did not destroy the iirmunological activity.The imriunolcgical stability of peptide B< 30-43 in EDTA-plasma (+37°) seems to be very good. In citrated and heparinized plasma the activity of this peptide seems to vanish quite fast. In spite of these results we have detected high levels of iirmunolcgical activitiy in citrated or heparinized patient plasma. The molecular distribution of the peptides detected in plasma by our RIA corresponded to a fragnent containing about 25 amino acids. This fragnent seemes to be rather stable in plasma. When this fragnent was degraded with elastase in vitro a peptide with a molecular size resembling BB 30-43 was obtained. Over 300 patient samples have been studied. About 20 per cent were positive and the highest levels were found in patients with ARDS, septicaemia, severe renal failure, pulmonary embolism, pneumonia and pulmonary congestion.
