Milk feeding and changes in intestinal permeability and morphology in the newborn.

The contrasting effects of natural versus cow's milk formula (CMF) on upper gastrointestinal development in the newborn were studied. The passive intestinal permeability of neonatal human infants and guinea pigs was measured using the nonmetabolisable markers lactulose and mannitol. Mucosal morphology was examined in guinea pigs by light microscopy. Nineteen full-term human infants and 63 guinea pigs were studied during the 1st week of extrauterine life. The naturally fed infants showed a decline in intestinal permeability to lactulose following the onset of feeding. This was not shared by those fed CMF. The CMF-fed guinea pigs showed a persistently higher intestinal permeability than the naturally fed animals throughout the 1st week of life. No differences were observed in the villous heights or crypt depths between feeding groups, but both showed an increase in intraepithelial lymphocyte number during the 1st week. Cow's milk formula may cause a persistently higher intestinal permeability, or natural feeding may promote a decline in permeability in the enterally fed newborn.