Specificity of infant gastric digestive conditions: new in vivo data from preterm
Résumé
-Objectives and study: The digestive functions are immature during the first months of life, especially
for preterm newborns (i.e. motility, enzymatic and secretory functions). The gastric digestion of
complex colloidal emulsions such as human milk and infant formulas is a key step which will further
modulate nutrient absorption and infant nutrition. Factors such as gastric acidification, emptying rate
and enzyme outputs are key parameters that play a role in the kinetics of hydrolysis and the
disintegration of these emulsions, and may be influenced by the nature of the meal and the age of
the infant. The purpose of this study was to characterize gastric contents and physiological
parameters of preterm infants in fasting state or after ingestion of raw, pasteurized or pasteurizedhomogenized
human milk.
-Methods: In vivo study was conducted at Rennes Hospital on preterm infants fed by a nasogastric
tube (NCT02112331). Newborns were included in two independent groups determining the type of
meals: A) raw and pasteurized human milk; B) pasteurized and pasteurized-homogenized human
milk. Gastric contents were collected twice a day, over six day. Gastric contents were collected
before meal ingestion and 35, 60 or 90 min after meal ingestion. Gastric volume and pH were
measured. Lipase activity was determined by titration of released free fatty acids from tributyrin (pHstat
technique, at pH 6 and pH 8, at 37°C). Gastric emptying rates and ratio of meal to secretions
were determined using two different meal markers: total fatty acids for the lipid phase and taurine
for the liquid phase. The markers were quantified respectively by gas and cation-exchange
chromatography.
-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 gastric
volume was 1.4 ± 1.6 mL/kg of body weight and fasting pH was 3.7 ± 1.0 (range: 1.7 to 5.6). Gastric
acidification 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 the
neonates’ limited capacity of acidification but also suggest the impact of frequent feeding. Still in
group A, at 35 min of digestion the gastric volume was higher for pasteurized than for raw human
milk (p < 0.05). Similar trends were observed in group B and will be further discussed. Some lipase
activity was measured in the fasting state; in postprandial aspirates the activity depended on the
meal ingested. The estimation of gastric emptying rates and ratio of meal to secretions determined
by lipid or liquid markers is an original approach. Values differed depending on the marker, revealing
a non-homogeneous emptying of the emulsion. It has been demonstrated (Marciani et al., 2007) that
emulsions 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 is
essential to optimize nutrition and oral drug delivery. Moreover, these data will be useful to develop
relevant in vitro models of infant digestion.