Effects of pH on alpha 1-antitrypsin activity in premature infants with idiopathic respiratory distress syndrome.

The inhibitory and specific activities of serum alpha 1-antitrypsin (1-AT) at pH levels of 8.20, 7.45, 7.35, 7.25 and 7.15, were studied in 66 neonates with idiopathic respiratory distress syndrome (IRDS) and in 82 healthy neonates. In vivo pH values were also correlated in both groups with the specific and inhibitory activities of 1-AT. Comparisons between healthy neonates and neonates with IRDS showed that in the latter, the inhibitory and specific activities of 1-AT were lower, with every pH assayed, together with twice a percentual decrease from pH 8.20 to pH 7.15 in both activities. No statistical correlation was established in the in vivo pH of infants in both groups with the inhibitory and specific activities of 1-AT. Results suggest two alternatives. The first one related to a molecular structure different from 1-AT in infants with IRDS, and the second one regarding changes in 1-AT produced by partial breakdown or modified by hypoxia, acidosis or both.