Prevention by ulinastatin of decreased carbonic anhydrase activity induced by PMN elastase in vitro

Disturbed carbon dioxide (CO2) elimination in adult respiratory distress syndrome (ARDS) has been considered to result from the dead space created by microthrombosis and vasoconstriction. However, another disturbance factor in CO2 elimination has been reported; the chemical dead space resulting from the inhibition of carbonic anhydrase (CA). This experiment was conducted to quantify the inhibition of CA activity by polymorphonucleocyte (PMN) elastase, which increases in ARDS. Different flasks containing solutions of CA, buffer, elastase, ulinastatin (an elastase antagonist), CA with PMN elastase, and CA with both PMN elastase and ulinastatin were prepared. Each flask was injected with sodium bicarbonate labeled with radioactive carbon (14C) and was shaken for 20 minutes; CA activity in each flask was measured by calculating the decrease in the coefficient (K) of 14C. It was observed that CA activity was inhibited dose-dependently by PMN elastase and that the inhibited activity was recovered by ulinastatin, which can inhibit PMN elastase. These findings indicate that CA activity in vitro could be inhibited by PMN elastase, which increases in ARDS, and suggests that disturbance of CO2 elimination could be reduced by using ulinastatin. It was concluded that ulinastatin could prevent the CA activity induced by PMN elastase in vitro.