Cessation of Uptake of Macromolecules by Neonatal Guinea Pig, Hamster and Rabbit Intestinal Epithelium (Closure) and Transport into Blood

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Abstract
Accumulating evidence indicates that nonselective absorption of macromolecules by neonatal intestinal epithelium may be a general phenomenon of the newly born. To gather further information on this point, neonatal guinea pigs, hamsters and rabbits were examined for their capacity to: a) internalize albumin and γ-globulin into their intestinal epithelium; and b) transport these internalized macromolecules into their blood. These same epithelia were monitored for pinocytosis using electron microscopy. It was concluded that the intestinal epithelium of these species of neonates nonselectively takes up macromolecules. However, guinea pigs transported none of the internalized macromolecules to the blood; hamsters transported only γ-globulin to the blood; and rabbits transported only γ-globulin into the blood provided the concentration of the gavaged dose is increased from 2 to 8% γ-globulin. The period of time after which neonates no longer had the capacity to internalize macromolecules into intestinal epithelium (coincident with the loss of pinocytotic activity) was called closure. For the guinea pig, closure occurred around 1 day of age; for the hamster around 5 days of age; and for the rabbit around 23 days of age.