TRYPSIN AND ELASTASE ACTIVITIES ARE INHIBITED AFTER A MEAL OF HUMAN MILK IN PRETERM INFANTS - COMPLEX FORMATION?

Our knowledge of duodenal proteolytic capacity in preterm infants is limited. We have no information about the activity of the various proteolytic enzymes after a meal of human milk at these early ages. The aim of the study was to analyse trypsin and elastase in duodenal juice by esterolytic and immunochemical methods before and after a human milk meal. Patients and methods: 16 preterm infants born at a gestational age of 23-30 weeks (birth weight 472-967 g) were studied at an age of 1-2 months (actual weight 816-1946 g). Duodenal juice was collected before and up to 120 minutes after a meal of human milk. Trypsin activity was determined with BAPNA and elastase with suc-tr-ala-p.nitroanilide as substrates. The presence of anionic and cationic trypsins and elastase was studied by immunoelectrophoresis and electroimmunoassay. Results: Trypsin activities (mean value, ranges) decreased from 150 ug/ml (0-340) before to 57 (0-175) after the meal. Corresponding values for elastases were 0.7 ug/ml (0.2-2.6) and 0.3 (0-1.6). In samples with “normal” trypsin activity anionic and cationic trypsin were immunoelectrophoretically located at their “normal” places. However, after the meal - in 12 out of 13 samples with no or low trypsin activity - the cationic trypsin had moved anodally. The anionic trypsin had moved cathodally. Cationic elastase was not detectable in 15 of the 16 infants - in one only small amounts were found. Anionic elastase was present in all samples. Conclusion: Cationic elastase has not yet been developed in preterm infants. After a human milk meal cationic and anionic trypsins form complexes - probably with proteins in human milk(alpha-1-antitrypsin, alpha-1-antichymo-trypsin or another protein?). These findings explain the slow protein digestion observed in very low birthweight infants and they may also contribute to the increased absorption of immunoactive protein occurring at this age.