Activation of the kallikrein-kinin system in premature infants with respiratory distress syndrome (RDS).

Plasma prekallikrein levels, kallikrein activity and antikallikrein levels were investigated in nine premature infants with respiratory distress syndrome (RDS) and six premature infants without. Plasma prekallikrein and kallikrein were determined with a chromogenic substrate measuring amidolytic activity. Antikallikrein was measured with a functional assay. In infants with severe RDS, prekallikrein levels were significantly reduced (median 58% of initial values (p less than 0.01) about 48 hours after onset of symptoms. In infants with moderate RDS prekallikrein level was reduced less, while in babies without RDS there were no significant changes in prekallikrein levels the first 5-7 days of life. Antikallikrein levels did not change significantly in any babies. The results suggest that the kallikrein-kinin system might be involved in RDS. This could explain several features of this syndrome such as hypotension and edema. Furthermore the findings show that homeostatic functions are altered in this disease, and they suggest that other cascade systems as the coagulation, fibrinolytic and complement system may be involved as well. The findings emphasize that trauma might be a significant pathogenetical factor for development of this syndrome and indicate that RDS is not simply a biochemical disease with lack of surfactant as the only pathogenetic factor.