No evidence for bradykinin hydrolysis in human erythrocyte suspensions: H NMR studies

Abstract

In view of their permeability to small peptides, it has been postulated that human erythrocytes may play a role in terminating the action of some circulating peptide hormones. Work using classical paper chromatographic techniques for detecting free amino acids indicated that the octapeptide, des-(Arg9)-bradykinin, enters these cells and its amino-terminal arginine residue is released by cytosolic aminopeptidase-P. We have used 1H NMR to monitor directly the release of arginine from bradykinin. The hydrolytic reaction rate in hemolysates, with an initial peptide concentration of 13.0 mmol l-1 was 6.5 mmol (1 packed red cell)-1 h-1. But no reaction was evident after a 4.5-h incubation with intact cells, thus contradicting the earlier suggestion that erythrocytes are involved in the primary inactivation of this hormone. This is consistent with our previous findings that the pentapeptide leu-enkephalin fails to enter human erythrocytes but that its lower-order degradation products may do so.

Pathways of bradykinin degradation in blood and plasma of normotensive and hypertensive rats

“…However, a quantitative determination of the role of cellular kininases in blood has not yet been performed. Apparently, the highly abundant erythrocytes appear to lack any kind of extracellular kininases (13), and the leukocytes and platelets are either inadequately furnished with activity, or the enzymes are not externalized on the cell surface of quiescent cells.…”