POSSIBLE INVOLVEMENT OF PLACENTAL PROTEASES IN BRADYKININ (BK) DEGRADATION

The hydrolysis of bradykinin (BK) by human placental subcellular fract ions and pregnancy sera was studied in the presence of inhibitors by m easuring amino acids liberated from BK by high-performance liquid chro matography. The effects of the inhibitors DL-2-mercaptomethyl-3-guanid inoethylthiopropionic acid (MGTA, for kininase I), phosphoramidon (for endopeptidase 24.11) and captopril and rentiapril (for angiotensin-co nverting enzyme [ACE, kininase II]) suggested the essential roles of t he above three proteases in BK degradation: among the three proteases, kininase I and endopeptidase 24.11 appeared to be the most important in kininase action in the placenta microsomes, whereas kininase I and ACE appeared to be the most important in kininase action in the placen tal cytosol, lysosome and pregnancy serum. Measurements of BK concentr ations in the umbilical arterial blood, umbilical venous blood and mat ernal plasma revealed higher concentrations in the mother than in the fetus. The present data suggest that degradation of BK in the placenta and pregnancy serum might contribute to the gradient of BK between mo ther and fetus.