Possible involvement of placental proteases in bradykinin (BK) degradation.

The hydrolysis of bradykinin (BK) by human placental subcellular fractions and pregnancy sera was studied in the presence of inhibitors by measuring amino acids liberated from BK by high-performance liquid chromatography. The effects of the inhibitors DL-2-mercaptomethyl-3-guanidinoethylthiopropionic acid (MGTA, for kininase I), phosphoramidon (for endopeptidase 24.11) and captopril and rentiapril (for angiotensin-converting enzyme [ACE, kininase II]) suggested the essential roles of the 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 placental cytosol, lysosome and pregnancy serum. Measurements of BK concentrations in the umbilical arterial blood, umbilical venous blood and maternal 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 mother and fetus.