Carboxypeptidase N concentration during cardiopulmonary bypass in humans

Carboxypeptidase N (CPN) is an inactivator of anaphylatoxins and kinins, peptides implicated in the pathogenesis of complications in extracorporeal circulation. To investigate whether the level of CPN is altered during cardiopulmonary bypass (CPB) we studied 15 patients undergoing cardiac surgery utilizing CPB. The concentration of CPN decreased to about 48% of the initial value upon initiation of CPB and remained low throughout the procedure. A similar decrease was observed in the level of alkaline phosphatase, an enzyme that was measured to assess the degree of haemodilution. When the data were normalized for dilution, no difference in the concentration of CPN was observed during CPB. Moreover, no changes in the concentration of CPN were observed when protamine was given to neutralize heparin and none of the 15 patients experienced any side-effects of protamine administration. We conclude that the decrease in CPN during CPB was due primarily to dilution and not to changes in CPN synthesis or catabolism. Protamine administration is not associated with significant changes in the level of CPN in patients who have an asymptomatic reversal of heparin anticoagulation.