of the ITI with antiprotease activity is easily split off and may enter the bronchial lumen and probably other extravascular compartments such as urine. In addition, it can be shown that All originates from AI by limited proteolysis. So far these inhibitors have only been tested against a small number of enzymes. All three inhibitors clearly inactivate bovine trypsin and chymotrypsin and human granulocytic elastase. Their action against granulocytic elastase may be of physiologic importance. It is known that during bronchitis considerable amounts of granulo- cytic elastase are found in tracheobronchial secretions. The inhibitors may, therefore, be considered a part of the pulmonary antiproteolytic defense. 1 Hochstrasser K, Schorn K, Rasche B, Lemparth K, Raffelt C. Isolation and characterization of a protease inhibitor from human bronchial secretions. Hoppe-Seyler's Z Physiol Chern 1972; 353:221-26 2 Ohlsson K, Tegner H, Akesson U. Isolation and partial characterization of a low molecular weight acid stable protease inhibitor from human bronchial secretion. Hoppe-Seyler's Z Physiol Chern 1977; 358:583-89 3 Hochstrasser K, Feuth H, Hochgesand K. Proteinase in- hibitors of the respiratory tract: Studies on the structural relationship between acid-stable inhibitors present in the respiratory tract, plasma and urine. In: Fritz H, Tscheche H, Greene LJ, Truscheit E, eds. Proteinase inhibitors: Bayer Symposium V, Berlin: Springer-Verlag, 1974; 111-16 Proteinase Inhibitors and Inhibitor Inactivation in Neonatal Airways Secretions* M. Bruce, Sc.D.; T. Boat, M.D.; R. Martin, M.D.; D. Dearborn, M.D.; and A. Fanaroff, M.D. Diminished activity of a 1 proteinase inhibitor (a 1 PI) obtained from lung lavage of cigarette smokers compared with a,PI obtained from non-smoking control subjects has been attributed to oxidation of the active site methionine of a,PI by oxidants of cigarette smoke.' This impaired antiproteinase activity is currently thought to be a significant factor in the development of pulmonary emphysema in chronic smokers. The sus- ceptibility of a,PI to oxidative inactivation has been demonstrated by in vivo and in vitro exposure to oxi- dants such as 0 3 , 2 chloramine T, 3 • 4 and N-chlorosuc- cinimide3 as well as to cigarette smoke. The effects of high concentrations of 0 2 on a,PI have not been previ- ously reported. Infants who develop respiratory distress frequently require high concentrations of inspired 0 2 ( Flo 2 ) and •case-Western Reserve University, Cleveland. Reprint requests: Dr. Bmce, Department of Pediatrics, Case Western Reserve University, Cleveland 44106 44S 24TH ASPEN LUNG CONFERENCE ventilatory assistance. In this study, airway secretions from infants treated with high concentrations of 0 2 were examined to determine whether chronic exposure to high Flo 2 results in oxidative inactivation of a,PI. We found a positive correlation between loss of ac- tivity of a,PI and duration of exposure to high concen- trations of 0 2 • It is possible that this loss of activity of a,PI plays a role in the pathogenesis of chronic lung disease in these infants. METHODS Airway secretions were collected from 4 term and 10 preterm intubated infants during routine endotracheal tube suctioning. Infants were suctioned at 2 hour intervals and secretions obtained from 3 or 4 suctionings were pooled and concentrated using a millipore immersible filter ( MW cut off = 30,000) . Concentrations of .. ,PI, 11 2 macrog\obulin and albumin in secretions were determined on radial immuno- diffusion plates. Prior to assay for activity of .. ,PI, lung secretions were dialyzed for 48 hr against Tris-HCL buffer (pH 8.1) or Tris-HCL with dithiothreitol (10 mM). The ability of "• PI to inhibit the action of porcine pancreatic elastase on succinyl- (ala) 3 -p-nitroanilide was determined. Inhibition of elastase activity by 11 1 PI was assayed by adding increas- ing amounts of bronchial secretions containing .. , PI to a constant amount of porcine pancreatic elastase (E). The elastase inhibitory capacity of bronchial secretions from ventilated infants on low 0., (Flo. 0.4) was compared with that of secretions from- on high concentrations of 0 2 (Fio 2 0.6). RESULTS As is shown in colurrm A of Table I, the molar ratios of a,PI /E required to inhibit I5X of the elastase ac- tivity were the same for infants on low 0 2 for I-9 days as for infants on high concentrations of 0 2 for I-2 days. In infants exposed to high 0 2 for 3-4 days, there was a signillcant increase in the molar ratio of a,PI/E re- quired for I5X inhibition of elastase activity. There was a further increase in the molar ratio of a,PI/E required for I5% inhibition in secretions of infants on high 0 2 for 6-I5 days. Although in our assay system, a molar ratio of puri- fied native a,PI / E of 2.4 results in IOO% inhibition of elastase activity, we observed complete inhibition only in infants on low Flo 2 and in infants on high Fio 2 for 1-2 days. Because of limited sample size and extent of inactivation of a,PI, it was, in many instances, not pos- sible to achieve 50X inhibition of elastase activity. The data in column B, Table I indicate that molar ratios of a,PI/E required for 50X inhibition of elastase activity (EA) were the same for infants on low Flo 2 as for those on high Flo 2 for I-2 days. Only in 1 of the infants on high 0 2 for 3-4 days did we see 50X inhibition of EA and the molar ratio of a,PI/E required to achieve 50% inhibition of EA was twice that required from infants on high 0 2 for I-2 days. In this group we were not able to achieve 50% inhibition in the other 2 infants at molar ratios of 2.4 and 5.2 (see footnote, Table I). Loss of activity of a,PI from infants on high Flo 2 for CHEST, 81: 5, MAY, 1982 SUPPLEMENT