Résumé
-Objectives and study: The digestive functions are immature during the first months of life, especiallyfor preterm newborns (i.e. motility, enzymatic and secretory functions). The gastric digestion ofcomplex colloidal emulsions such as human milk and infant formulas is a key step which will furthermodulate nutrient absorption and infant nutrition. Factors such as gastric acidification, emptying rateand enzyme outputs are key parameters that play a role in the kinetics of hydrolysis and thedisintegration of these emulsions, and may be influenced by the nature of the meal and the age ofthe infant. The purpose of this study was to characterize gastric contents and physiologicalparameters of preterm infants in fasting state or after ingestion of raw, pasteurized or pasteurizedhomogenizedhuman milk.-Methods: In vivo study was conducted at Rennes Hospital on preterm infants fed by a nasogastrictube (NCT02112331). Newborns were included in two independent groups determining the type ofmeals: A) raw and pasteurized human milk; B) pasteurized and pasteurized-homogenized humanmilk. Gastric contents were collected twice a day, over six day. Gastric contents were collectedbefore meal ingestion and 35, 60 or 90 min after meal ingestion. Gastric volume and pH weremeasured. Lipase activity was determined by titration of released free fatty acids from tributyrin (pHstattechnique, at pH 6 and pH 8, at 37°C). Gastric emptying rates and ratio of meal to secretionswere determined using two different meal markers: total fatty acids for the lipid phase and taurinefor the liquid phase. The markers were quantified respectively by gas and cation-exchangechromatography.-Results: Infants from group A (n=12) were 16 to 53-day old at the first day of the study. On average(±SD), birth weight was 1.4 ± 0.3 kg and gestational age 29.6 ± 1.0 weeks. In group A, fasting gastricvolume was 1.4 ± 1.6 mL/kg of body weight and fasting pH was 3.7 ± 1.0 (range: 1.7 to 5.6). Gastricacidification was not impacted by meal (p > 0.05). On average, pH values of gastric digesta were 6.0 ±0.6, 5.2 ± 0.7 and 4.4 ± 0.8 at 35, 60 and 90 min after ingestion, respectively. These data confirm theneonates’ limited capacity of acidification but also suggest the impact of frequent feeding. Still ingroup A, at 35 min of digestion the gastric volume was higher for pasteurized than for raw humanmilk (p < 0.05). Similar trends were observed in group B and will be further discussed. Some lipaseactivity was measured in the fasting state; in postprandial aspirates the activity depended on themeal ingested. The estimation of gastric emptying rates and ratio of meal to secretions determinedby lipid or liquid markers is an original approach. Values differed depending on the marker, revealinga non-homogeneous emptying of the emulsion. It has been demonstrated (Marciani et al., 2007) thatemulsions that are destabilized in the gastric compartment can modulate the hormonal feedback(cholecystokinin).-Conclusion: This study presents a unique set of data illustrating the specificity of preterm infants’gastric digestive conditions. Understanding the physiological environment in the infant gastric tract isessential to optimize nutrition and oral drug delivery. Moreover, these data will be useful to developrelevant in vitro models of infant digestion.